LAO PEOPLE’S DEMOCRATIC REPUBLIC PEACE INDEPENDENCE DEMOCRACY UNITY PROSPERITY Lao Electric Power Technical Standards December, 2018 Preface Energy is a key input and important factor for economic development of any country or people. Investing in infrastructure creation including for energy production leads to human socio-economic development which is the key goal for any country. A well developed and efficient power sector is a basic requirement and an important mechanism for advancement and to achieve national objectives of improving the living standards of the people, and contribute to sustainable socio-economic development. Lao PDR is a country with abundant natural resources, particularly water resources that provide an excellent basis for the energy sector to generate hydro power. Government of Lao PDR has rightly taken this route and given high priority to development of the hydro power sector. Based on international practices and standards and with cooperation and assistance from Government of Japan, electrical technical standards were developed under the Electric Power Technical Standards Project. These technical standards were adopted in the year 2004 by Lao Government through its Ministry of Energy and Mines as the Lao PDR Electric Power Technical Standards (LEPTS). The LEPTS cover the main principles governing the management of electricity activities such as planning, design, construction, operation, generation, transmission, distribution and electricity services. The LEPTS, by specifying uniform, consistent and technically correct practices, aimed to encourage greater efficiency in the industry. Over the years, it was observed that many provisions of LEPTS needed updating as they were seen to be too general, required to be more precise and be able to address the detailed design procedures. In view of this, World Bank stepped forward to provide necessary support and assistance under the World Bank aided “Technical Assistance for Capacity Building in the Hydropower and Mining Sectors” project. PricewaterhouseCoopers Pvt Ltd, India (PwC India) and Entura, had been appointed as the consultants to support Government of Lao PDR to put in place a framework for proper development of the power sector including the review and subsequent modification of LEPTS documents. Entura carried out a detailed review and subsequently modification to the LEPTS documents keeping in mind the current scenario of the power sector development in Lao PDR as well as the recent advances in technology, newly adopted international standards and changing requirements of Lao PDR’s hydropower development program. The adequacy and compatibility of new international standards for design, construction and operation of hydropower was analyzed and studied to ensure a coherent technical framework for the sector. The guidelines have been revised ensuring that they are consistent with the Electricity Law and other guidelines in force. The Ministry of Energy and Mines, Government of Lao PDR takes this opportunity to thank the World Bank and their consultant PwC and Entura for the valuable assistance they have provided in reviewing and updating of the LEPTS. The Ministry would also like to thank all participating organizations and staff for their cooperation in successfully establishing these Technical Standards. The Ministry recognizes that any standards should not be considered rigid and inflexible and should change with new developments and technical advances in the field. It would therefore welcome comments and suggestions from the users and would oversee appropriate amendments to these Technical Standards in response to industry experience to ensure that they remain relevant and effective in the long term. List of Project Members for Initial Document Project Director Mr. Houmphone BULYAPHOL (Chapter 1‐3) Director General of DOE, MIH Chief Advisor Dr. Shigenori KURODA (Chapter 1‐3) JICA Expert Hydropower Civil Engineering Group Mr. Takashi TADA, JICA Expert (Chapter 2) Mr. Voradeth PHONEKEO, DOE Staff Mr. Phonesavanh PHIMMASONE , DOE Staff Mr. Phoukhong SENGVILAY, DOE Staff Mr. Vantheva BOUKHASITH, EDL Staff Hydropower Plant/Substation Group (Chapter 3: 3‐1, 3‐2, 3‐3 and 3‐4) Mr. Hiroaki NISHIGAMI , JICA Expert Mr. Sisoukan SAYARATH, DOE Staff Mr. Viengsay CHANTHA, DOE Staff Mr. Khampa SIRIVONG, EDL Staff Mr. Douangpy SOUVANNACHITH, EDL Staff Transmission Group Mr. Takahiro ISHIMARU, JICA Expert (Chapter 3: 3‐1, 3‐2, 3‐3 and 3‐5) Mr. Phethsavanh RATTANATHONGXAY, DOE Staff Mr. Vithounlabandid THOMMABOUT, DOE Staff Mr. Sengkham THANIVONG, EDL Staff Distribution Group Mr. Munenori OTA, JICA Expert (Chapter 3: 3‐1, 3‐2, 3‐3, 3‐6 and 3‐7) Mr. Houmphan VONGPHACHAN, DOE Staff Mr. Vanhdy VILAYSANE, EDL Staff Mr. Thammanoune NAKHAVITH, DOE Staff Mr. Na NAOPHAKDY, EDL Staff Mr. Mixay CHITTARATH, EDL Staff Mr. Maypheth PHONPHILA, EDL Staff Project Manager Dr. Somboune MANOLOM Director of Cabinet, MIH Coordinator Mr. Masaaki DOI, JICA Expert List of Project Members for 2018 Document Government of Lao PDR Mr. Sychath BOUTSAKITTIRATH, Director General, Department of Energy Management Mr. Bouathep MALAYKHAM, Deputy Director General, Department of Energy Management Mr. Houmphanh VONGPHACHANH, Deputy Director General , Department of Energy Management Dr. Phoukhong SENGVILAY, Director of Division, Department of Energy Management Mr. Viengsay CHANHTHA, Director of Division, Department of Energy Management Mr. Phouxay VIENGVIXAY, Director of Division, Department of Energy Management Mr. Lair PHIMPHISANE, Deputy Director of Division, Department of Energy Management Mr. Bounthavee CHANHTANGEUN, Deputy Director of Division, Department of Energy Management World Bank Mr. Satoru Ueda, Lead Dam Specialist Mr. Takafumi Kadono, Senior Energy Specialist Entura/ PwC India Sonam Tshering, Team Leader, PwC India Dr. P.C. Jose, Hydropower Expert, Entura Mr. Zafarul Hasan, Dam Specialist, Entura Mr. Narendra Arora, Electrical Expert, Entura Dr. Tapanjyoti Mukhopadhyay, Geological and Geotechnical Expert, Entura Mr. Ajit Garg, Project Manager, Entura Mr. Praveen Thakur, Hydropower Expert, Entura Mr. Subhrajit Datta Ray, Director, PwC India Multiconsult UK Christopher Grant, Technical Director Table of Contents Chapter 1 General Provisions Article 1 Purpose of Technical Standards............................................................................................1-175 Article 2 Scope of Technical Standards................................................................................................1-175 Article 3 Conformity to the Technical Standards................................................................................2-175 Article 4 Nomination of Chief Engineers ..............................................................................................2-175 Article 5 Examination and Inspection ...................................................................................................3-175 Article 6 Order of Remedy for Conformance to Technical Standards..............................................4-175 Article 7 Obligation for Reporting........................................................................................................5-175 Chapter 2 Hydropower Civil Engineering Facilities 2-1 General Article 8 Definitions…………………………………………………………………............................8-175 2-2 Fundamental Requirements Article 9 Prevention of Overtopping from Non-overflow Sections of Dams .................................... 9-175 Article 10 Dam Stability ......................................................................................................................... 9-175 Article 11 Prevention of Seepage Failure of Dams ............................................................................... 9-175 Article 12 Prevention of Serious Deformation and Cracking of Dams............................................... 9-175 Article 13 Prevention of Failure of Waterways and Other Facilities.................................................. 9-175 Article 14 Prevention of Failure of Powerhouses and Other Facilities............................................... 9-175 Article 15 Prevention of Seepage Failure of Ground around a Reservoir .........................................10-175 Article 16 Prevention of Damage to Upstream and Downstream Areas ............................................ 10-175 2-3 Dams 2-3-1 Common Rules Article 17 Inflow Design Flood............................................................................................................... 10-175 Article 18 Basic Water Levels ................................................................................................................ 12-175 Article 19 Freeboard ............................................................................................................................... 13-175 Article 20 Loads......................................................................................................................................14-175 Article 21 Dam Foundations................................................................................................................. 15-175 Article 22 Prevention of Serious Water Leakage from Dams ........................................................... 15-175 Article 23 Monitoring and Inspections ................................................................................................ 16-175 2-3-2 Concrete Dams Article 24 Concrete Materials .............................................................................................................. 16-175 Article 25 Foundations for Concrete Dams......................................................................................... 16-175 Article 26 Stability of Concrete Gravity Dams ................................................................................... 17-175 Article 27 Stability of Arch Dams ........................................................................................................ 19-175 Article 28 Structural Details of Concrete Dam Body ......................................................................... 20-175 Article 29 Temperature Regulation for Concrete Dam Body ........................................................... 20-175 2-3-3 Fill Dams Article 30 Embankment Materials ...................................................................................................... 21-175 Article 31 Foundations for Fill Dams .................................................................................................. 22-175 Article 32 Stability of Fill Dams ........................................................................................................... 22-175 Article 33 Restrictions on Facilities such as Discharge Facilities ...................................................... 23-175 Article 34 Design for Homogeneous Type Fill Dams.......................................................................... 23-175 Article 35 Design for Zoned Type Fill Dams....................................................................................... 23-175 Article 36 Design for Surface Diaphragm Type Fill Dams ................................................................ 23-175 2-3-4 Other Types of Dams Article 37 Other Types of Dams........................................................................................................... 23-175 2-3-5 Spillways and Other Discharge Facilities Article 38 Spillways............................................................................................................................... 24-175 Article 39 Spillway Gates and Auxiliaries........................................................................................... 24-175 Article 40 Other Discharge Facilities................................................................................................... 25-175 2-4 Waterways Article 41 Common Rules..................................................................................................................... 25-175 Article 42 Intakes .................................................................................................................................. 26-175 Article 43 Settling Basins ...................................................................................................................... 26-175 Article 44 Headraces ............................................................................................................................. 26-175 Article 45 Surge Tanks and Head Tanks ............................................................................................ 27-175 Article 46 Penstocks .............................................................................................................................. 28-175 Article 47 Tailraces ............................................................................................................................... 29-175 Article 48 Gates, Valves, and Auxiliaries ............................................................................................ 29-175 2-5 Powerhouses and Other Facilities Article 49 Powerhouses ......................................................................................................................... 29-175 Article 50 Other Facilities..................................................................................................................... 30-175 2-6 Reservoirs Article 51 Prevention of Landslide ...................................................................................................... 30-175 Article 52 Sedimentation and Water Quality ..................................................................................... 30-175 2-7 Downstream Article 53 Regulation of Discharge to Downstream Areas ................................................................ 30-175 Article 54 Facilities to Discharge to Downstream Areas.................................................................... 30-175 Chapter 3 Electrical Facilities 3-1 General Article 55 Definitions ............................................................................................................................ 32-175 Article 56 Standard Frequency, Standard Voltages and Standard Test Voltages .......................... 33-175 Article 57 Classification ........................................................................................................................ 35-175 3-2 Fundamental Requirements Article 58 Prevention of Electric Shock and Fire Caused by Electrical Facilities ........................... 38-175 Article 59 Insulation of Electrical Circuits against Grounds ............................................................ 38-175 Article 60 Provision of Earthing on Necessary Points in Electrical Facilities .................................. 39-175 Article 61 Protection against Overcurrent and Earth Faults ............................................................ 39-175 Article 62 Isolation from High-voltage and Medium-voltage Electrical Facilities .......................... 39-175 Article 63 Prevention of Danger Due to Breakage of Electrical Conductors ................................... 39-175 Article 64 Prevention of Damage to Other Facilities.......................................................................... 39-175 Article 65 Prevention of Danger Due to Collapse of Supporting Structures.................................... 39-175 Article 66 Prevention of Electrical and Magnetic Interference......................................................... 39-175 Article 67 Prevention of Serious Obstacles to Power Generation and Power Supply, and Prevention of Damage to Other Electrical Facilities Caused by Damage and Destruction of Electrical Facilities ..................................................................................... 39-175 Article 68 Prevention of Pollution........................................................................................................ 40-175 3-3 Common Rules for Electrical Facilities 3-3-1 Protective Safety Installations Article 69 Prevention of Entry of Any Person Other than Operators to Closed Electrical Operating Areas where High-voltage and Medium-voltage Electrical Facilities are Installed....................................................................................... 40-175 Article 70 Protection of Operators against Dangers of High-voltage and Medium-voltage Electrical Facilities in a Closed Electrical Operating Area ................. 41-175 Article 71 Prevention of Danger of Low-voltage Hydropower Electrical Plants ............................. 43-175 Article 72 Prevention of Climbing onto Supporting Structures........................................................ 43-175 Article 73 Prevention of Damage by Small Animals to Electrical Facilities .................................. 43-175 Article 74 Prevention of Damage by Rainwater to Electrical Facilities ........................................... 43-175 Article 75 Prevention of Fire Caused by Electrical Equipment ........................................................ 44-175 3-3-2 Prevention of Electrical and Magnetic Interference Article 76 Prevention of Electrical Inductive Interference and Electrical Wave Interference ... 45-175 3-3-3 Prevention of Pollution Article 77 Prevention of Pollution by Insulating Oil .......................................................................... 45-175 Article 78 Prevention of Emission of SF6 Gas .................................................................................... 46-175 3-4 Hydropower Electrical Plants, Substations and Switching Stations 3-4-1 Electrical Equipment 3-4-1-1 Insulation Article 79 Insulation Co-ordination..................................................................................................... 46-175 Article 80 Restriction against Overvoltage ......................................................................................... 47-175 Article 81 Insulation Strength of Electric Circuits in Electrical Equipment ................................... 48-175 Article 82 Insulating Clearance for Bus Bars ..................................................................................... 52-175 3-4-1-2 Thermal Strength and Mechanical Strength Article 83 Thermal Strength of Electrical Equipment ....................................................................... 52-175 Article 84 Mechanical Strength of Electrical Equipment against Short-circuit Current ............... 53-175 Article 85 Mechanical Strength of Hydraulic Turbines and Generators ......................................... 54-175 3-4-1-3 Particularities of Equipment Article 86 Prevention of Damage to Hydraulic Turbines .................................................................. 54-175 Article 87 Prevention of Damage to Pressure Tanks.......................................................................... 55-175 Article 88 Prevention of Damage to Bus Bars..................................................................................... 55-175 3-4-2 Protection, Monitoring and Control Systems Article 89 Monitoring and Control Systems ....................................................................................... 56-175 Article 90 Monitoring and Control Devices ........................................................................................ 57-175 Article 91 Protection Systems............................................................................................................... 60-175 Article 92 Protective Devices for Electrical Equipment..................................................................... 61-175 Article 93 Protective Devices for Electrical Lines .............................................................................. 63-175 Article 94 Emergency Water Interception Devices ............................................................................ 63-175 3-4-3 Earthing Arrangement Article 95 Earthing Arrangement of Electrical Facilities .................................................................. 63-175 Article 96 Particularities of Earthing Arrangement .......................................................................... 65-175 3-5 Transmission Lines 3-5-1 Overhead Transmission Conductors Article 97 Properties of Electrical Conductors ................................................................................... 66-175 Article 98 Load on Overhead Transmission Conductors and Safety Factor ................................... 67-175 Article 99 Jointing and Branching of Electrical Conductors ............................................................ 68-175 3-5-2 Insulator for Overhead Transmission Lines Article 100 Mechanical Strength of Insulators for Overhead Transmission Lines ........................... 68-175 3-5-3 Dielectric Strength of Overhead Transmission Lines Article 101 Clearance between Supporting Structures and Electrical Conductors .......................... 70-175 Article 102 Dielectric Strength of Overhead Transmission Lines....................................................... 70-175 3-5-4 Supporting Structures Article 103 Steel Structural Members of Supporting Structures........................................................ 70-175 Article 104 Loads on Supporting Structures and Safety Factor ......................................................... 77-175 Article 105 Loads on Foundations of Supporting Structures and Safety Factor............................... 78-175 Article 106 Reinforcement of Overhead Transmission Lines.............................................................. 78-175 Article 107 Reinforcement by Guys....................................................................................................... 79-175 3-5-5 Regulations for Installation Article 108 Clearance between Overhead Ground Wires and Electrical conductors ....................... 79-175 Article 109 Height of Overhead Transmission Conductors and Limitation of Span ........................ 80-175 Article 110 Clearance between Plants and Overhead Transmission Conductors ............................. 81-175 Article 111 Restrictions in Urban Areas ............................................................................................... 81-175 Article 112 Regulations for Side-by-side Installation and at Adjacency to and Crossing With other Objects ........................................................................................................... 83-175 3-5-6 Particulars of Installation for Side-by-side Use and at Adjacency to and Crossing with Other Objects 3-5-6-1 Side-by-side Use Installation with Other Objects Article 113 Installation with Distribution Conductors ........................................................................ 85-175 Article 114 Installation with Telecommunication Conductors............................................................ 86-175 Article 115 Low-voltage Appliances on Towers ................................................................................... 87-175 3-5-6-2 Installations at Adjacency to and Crossing with Other Objects Article 116 Adjacency to and Crossing with Buildings ........................................................................ 88-175 Article 117 Adjacency to and Crossing with the Roads ....................................................................... 89-175 Article 118 Adjacency to and Crossing with Distribution Conductors and Telecommunication Conductors ..................................................................................... 91-175 Article 119 Adjacency to and Crossing with Transmission Conductors ............................................ 94-175 Article 120 Adjacency to and Crossing with Other Facilities.............................................................. 95-175 3-5-7 Protection against Lightning and Falling Trees Article 121 Protection against Lightning .............................................................................................. 97-175 Article 122 Protection against Falling Trees ......................................................................................... 97-175 3-5-8 Underground Transmission Lines 3-5-8-1 Dielectric Strength of Underground Transmission Lines Article 123 Dielectric Strength of Underground Transmission Lines ................................................ 97-175 3-5-8-2 Cables of Underground Transmission Lines Article 124 Properties of Underground Cables .................................................................................... 98-175 Article 125 Jointing of Underground Cables ........................................................................................ 99-175 Article 126 Earthing of Underground Cables and Joint Boxes ........................................................... 99-175 Article 127 Prevention of Over-voltage for Underground Cables ...................................................... 99-175 3-5-8-3 Underground Installation of Cables Article 128 Underground Installation of Cables...................................................................................100-175 Article 129 Indication of Buried Cables ................................................................................................ 100-175 Article 130 Structure of Conduits, Culverts and Manholes ................................................................ 101-175 3-5-8-4 Particulars of Prevention against Underground Electrical Inductive Interference Article 131 Protection of Underground Telecommunication Lines from Electrical Inductive Interference .....................................................................................................102-175 3-5-8-5 Underground Installations at Adjacency to and Crossing with Other Objects Article 132 Adjacency to and Crossing with Underground Telecommunication Lines ....................102-175 Article 133 Adjacency to and Crossing with Underground Distribution Lines.................................103-175 Article 134 Adjacency to and Crossing with Other Underground Objects........................................103-175 3-5-9 Special Transmission Lines Article 135 Underwater Transmission Lines ....................................................................................... 104-175 Article 136 Transmission Lines Over Bridges ..................................................................................... 104-175 3-6 Distribution lines 3-6-1 Common Rules for Distribution Lines Article 137 Allowable Voltages for Distribution Lines .......................................................................105-175 Article 138 Insulation of Distribution Lines and User's Sites............................................................ 105-175 Article 139 Earthing of Distribution Lines and User's Sites............................................................... 106-175 Article 140 Equipment and Device Installations for Distribution Lines ........................................... 109-175 Article 141 Overcurrent Breakers ....................................................................................................... 110-175 Article 142 Earth Fault Breakers ........................................................................................................ 112-175 Article 143 Surge Arresters .................................................................................................................. 113-175 3-6-2 Overhead Distribution Lines 3-6-2-1 Overhead Distribution Conductors Article 144 Properties of Distribution Conductors ........................................................................... 114-175 Article 145 Load for an Overhead Distribution Lines and Safety Factor ....................................... 117-175 Article 146 Jointing of Overhead Distribution Conductors ..............................................................119-175 Article 147 Dielectric Strength of Overhead Distribution Lines.......................................................120-175 Article 148 Guard lines, Guard Nets and Protection Devices .........................................................121-175 3-6-2-2 Supporting Structures of Distribution Lines Article 149 Supporting Structures of Distribution Lines.................................................................. 122-175 Article 150 Load for Supporting Structures of Distribution Lines and Safety Factor .................. 124-175 Article 151 Load for Foundation of Supporting Structures of Distribution Lines and Safety Factor................................................................................................................... 129-175 Article 152 Reinforcement for Supporting Structures of Distribution Lines by Guys and so on ..130-175 3-6-2-3 Regulation for Installation on Distribution Lines Article 153 Height of Overhead Distribution Conductors ................................................................. 133-175 Article 154 Regulation of Distribution Lines at Adjacency to and Crossing with Other Objects.. 134-175 3-6-2-4 Particularities of Distribution Lines for Joint Use and Side by Side Use with Other Objects Article 155 Joint Use and Side-by-side Use of Distribution Lines with Other Objects ................... 141-175 3-6-3 Service Drop Lines Article 156 Overhead Service Drop Lines........................................................................................... 143-175 Article 157 Exterior Wall Lines at Consumer Facilities .................................................................... 144-175 Article 158 Party Service Drop Lines .................................................................................................. 147-175 3-6-4 Power Metering Article 159 Power Metering ................................................................................................................ 147-175 3-6-5 Underground Distribution Lines Article 160 Properties of Underground Distribution Cables and Jointing ..................................... 150-175 Article 161 Installation of Underground Distribution Cables .......................................................... 152-175 Article 162 Indication of Buried Distribution Cables ........................................................................ 153-175 Article 163 Underground Distribution Lines at Adjacency and Crossing with Other Objects...... 153-175 3-6-6 Special Distribution Lines Article 164 Over water and Under water Distribution Lines............................................................ 154-175 Article 165 Distribution Line over Bridge and Others ..................................................................... 155-175 3-7 User’s Sites Electrical Installations 3-7-1 Indoor Installations Article 166 Restriction of Indoor Lines Voltage ................................................................................. 157-175 Article 167 Restriction of Bare Conductors ....................................................................................... 157-175 Article 168 Electrical conductors used for indoor wirings ................................................................ 157-175 Article 169 Switching Devices at the Indoor Main Lines................................................................... 158-175 Article 170 Indoor Wiring Utensils...................................................................................................... 158-175 Article 171 Indoor Electrical equipments and Appliances ................................................................ 158-175 Article 172 Prevention of Obstacles caused by high frequency Current.......................................... 159-175 Article 173 Over Current Circuit Breakers for Electric Motors ...................................................... 159-175 Article 174 Installation of Mains for Electrical Circuits.................................................................... 160-175 Article 175 Installation of Branch Circuits ........................................................................................ 161-175 Article 176 Allowable Current of Indoor Wirings .............................................................................163-175 Article 177 Indoor Wiring Works........................................................................................................ 164-175 Article 178 Indoor Wirings for Adjacency and Crossing .................................................................. 168-175 Article 179 Indoor Installations for Electric Lamps .......................................................................... 169-175 Article 180 Mobile Electrical Wirings ................................................................................................. 169-175 3-7-2 Outdoor Installations Article 181 Outdoor Installations ....................................................................................................... 170-175 3-7-3 Special Installations Article 182 Traffic Signals ....................................................................................................................172-175 Article 183 Public Streetlamps ............................................................................................................. 172-175 Article 184 Submarine Lamps ............................................................................................................. 173-175 Lao People’s Democratic Republic Peace Independence Democracy Unity Prosperity Ministry of Energy and Mines LAO ELECTRIC POWER TECHNICAL STANDARDS Chapter 1 General Provisions Article 1 Purpose of Technical Standards The purpose of the Lao Electric Power Technical Standards (hereinafter referred to as the “Technical Standards”) founded on Article 33 of the Law on Electricity 2018, is to prescribe the fundamental requirements for power facilities and technical contents that should satisfy the fundamental requirements. The Technical Standards also include the Lao Dam Safety Guidelines and the power facilities involving dams should also comply with the Lao Dam Safety Guidelines. The Technical Standards are contemplated to meet the four (4) principles as follows: Power facilities shall not harm the human body and damage any object; The power facilities shall be installed so as not to magnetic interference that may affect other electrical facilities; There shall be of no significant effect on power supply despite of the power facilities being broken down or damaged, and Installation of the power facilities shall comply with the applicable Lao environmental laws and regulations and should have no or minimal adverse impact on the surrounding environment. cause any electrical and “The power facilities” are defined as to include, amongst others, hydropower stations, dams, substations, switching stations, transmission lines, distribution lines and users’ sites and be composed of hydropower civil engineering facilities (as prescribed in Chapter 2) and electrical facilities (as prescribed in Chapter 3). “The hydropower civil engineering facilities” are defined as civil engineering facilities, such as dams, waterways, and powerhouses, of the hydropower station. “The electrical facilities” are defined as to include electrical conductors, machines, apparatuses and devices, equipment, and supporting structures (except for the hydropower civil engineering facilities), which are to be installed or erected for generation, transformation, transmission or distribution or for use of electricity. Article 2 Scope of Technical Standards The Technical Standards shall apply to the power facilities to be newly constructed and _________________________________________________________________________________________________________________________________________ Page 1 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) rehabilitated /upgraded in course of design, under construction and in operation in the country of Laos. Article 3 Conformity to the Technical Standards An owner intending to newly install, rehabilitate, and operate a power facility shall design, construct, operate, and maintain/administer such facility so as to conform to the requirements as prescribed in the Technical Standards. The Technical Standards provide for the fundamental requirements concerning the power facilities and such technical contents that should satisfy the fundamental requirements. The technical contents contained in Section 2-3 to Section 2-7 and Section 3-3 to Section 3-7 may not cover all the technical contents that should satisfy the fundamental requirements set forth in Section 2-2 and Section 3-2, and if proposed alternative should have sufficient technical basis to fulfil the fundamental requirements, such alternative shall be judged to conform to the fundamental requirements. The “owner” used in this Article shall mean any organization, the Government and provincial administrative organs, state owned enterprises, private enterprises or persons that are authorized to engage in the electricity business in accordance with Article 36, Article 38, Article 42 and Article 78 of the Law on Electricity 2018. With respect to any power facility that is already being operated, power facility under construction and power facility of which design has been completed at the time of enforcement of the 2018 amended Technical Standards, the owner shall try to do his utmost so that such power facilities conform to the fundamental requirements within the limits of possibility. Article 4 Appointment of Chief Engineers The owner shall nominate chief engineers responsible for the technical matters in the fields of design, construction and operation concerning the power facilities respectively, and submit a notice of such nomination to the Ministry of Energy and Mines for its approval under its responsibility in compliance with article 65, 67, 90, 104 and 105 of Law on Electricity 2018. 1. Registered hydropower civil engineers who are nominated, hereinafter referred to as "registered hydropower civil engineers", shall be responsible for technical matters on design, construction, and operation of hydropower civil engineering facilities shall assume duties as prescribed items below: (1) Handover between the registered hydropower civil engineer in design and the registered hydropower civil engineer in charge of construction; charge of The registered hydropower civil engineer responsible for the technical matters in design and the registered hydropower civil engineer responsible for the technical matters in construction shall conduct taking-over of their duties based on the documents with respect to matters to be attended to for design and construction of the hydropower civil engineering facilities concerned. Also, the owner shall report the contents of the taking-over to the Ministry of Energy and Mines; (2) Handover between the registered hydropower civil engineer in charge of construction and the registered hydropower civil engineer in charge of operation; The registered hydropower civil engineer responsible for the technical matters in construction and the registered hydropower civil engineer responsible for the technical matters in operation shall conduct taking-over of their duties based on the documents with respect to matters to be attended to for design, construction and operation of the hydropower civil engineering facilities concerned. _________________________________________________________________________________________________________________________________________ Page 2 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Further, the owner shall report the contents of the taking-over to the Ministry of Energy and Mines; (3) Preparation and updation of Emergency Action Plan The registered hydropower civil engineer responsible for the technical matters shall be responsible for preparation of emergency action plan prior to start of construction, reservoir impoundment and operation in compliance with the Lao Dam Safety Guidelines. The registered hydropower civil engineer responsible for operation shall regularly review the emergency action plan during operation and keep it updated. (4) Investigation of accidents during construction and operation. The registered hydropower civil engineer responsible for the technical matters in construction and operation shall, if there arises any accident of the hydropower civil engineering facilities concerned, investigate damage, cause, etc. of such accidents. 2. Registered electrical engineers who are nominated, hereinafter referred to as "registered electrical engineers", shall be responsible for technical matters on design, construction, and operation of electrical facilities shall assume duties as prescribed items below: (1) Handover between the registered electrical engineer in charge of design and the registered electrical engineer in charge of construction. The registered electrical engineer responsible for the technical matters in design and the registered electrical engineer responsible for the technical matters in construction shall conduct taking-over of their duties based on the documents with respect to matters to be attended to for design and construction of the electrical facilities concerned. Also, the owner shall report the contents of the taking-over to the Ministry of Energy and Mines. (2) Handover between the registered electrical engineer and the registered electrical engineer in charge of operation. in charge of construction The registered electrical engineer responsible for the technical matters in construction and the registered electrical engineer responsible for the technical matters in operation shall conduct taking-over of their duties based on the documents with respect to matters to be attended to for design and operation of the electrical facilities concerned. Further, the owner shall report the contents of the taking-over to the Ministry of Energy and Mines. 3. Investigation of accidents during construction and operation. The registered electrical engineer responsible for the technical matters in construction and operation shall, if there arises any accident of the electrical facilities concerned, investigate damage, cause, etc. of such accidents. Article 5 Examination and Inspection The owner shall, in conducting design, construction and operation of any power facility, undertake examination and inspection to comply with requirements laid out in Article 110 of Law on Electricity 2018 and also in compliance with the Lao Dam safety Guidelines. The owner shall cooperate with the Ministry of Energy and Mines in conducting the examination and inspection. The owner will provide a detailed examination and inspection schedule and inspection reports including inspection reports during operational period, depending on the classification of the _________________________________________________________________________________________________________________________________________ Page 3 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) project as per Article 17. The following minimum examination and inspection will be conducted by the Ministry of Energy and Mines: 1. (1) Examination and inspection concerning the hydropower civil engineering facilities shall be prescribed items below: Examination before commencement of construction Examination shall be conducted as to whether the hydropower civil engineering facilities concerned conform to the Technical Standards prior to commencement of the construction. (2) Inspection of foundation In principle, in the case that the dam body height is 15 metres or more, or in the case that the type of the dam is special, or in the case that the permeability of the dam foundation before taking countermeasures is high, or in the case that there is a possibility that there is a large weak stratum, of the foundation, with insufficient strength before taking countermeasures; then on-site inspection of the foundation on which the dam is to be constructed shall be conducted to check whether the foundation is appropriate as a base of the dam. This shall be conducted after completion of excavation for the dam foundation and before construction of the dam body. Also, a spillway foundation categorized as “Extreme” and “High” in the dam classification in Article 17 shall be conducted to inspect as well as a dam case. (3) Inspection prior to first impounding The hydropower civil engineering facilities shall be inspected for its conformance with the Technical Standards prior to the start of first impounding. 2. Examination and inspection concerning the electrical facilities shall be prescribed items below: (1) Examination before commencement of construction Examination shall be conducted as to whether the electrical facilities concerned conform to the Technical Standards prior to commencement of the construction. (2) Examination before commencement of operation and inspection before commencement of operation. Examination shall be conducted as to whether the electrical facilities concerned conform to the technical standards before commencement of operation of such electrical facilities. In addition, where necessary, inspections shall be conducted before commencement of operation and also during operation of such civil and electrical facilities. Article 6 Order of Remedy for Conformance to Technical Standards In case any design, construction, operation, electrical installation, expansion, repair and maintenance of equipment and Civil engineering and Electrical Facilities do not meet the technical standards or quality, the Ministry of Energy and Mines may issue a notice to the owner to improve, repair or fix such non-compliance to make it consistent with Technical Standards. In the event of high risk, the Ministry of Energy and Mines may temporarily or permanently suspend the construction and operation and the owner shall not be compensated for any claim whatsoever due to such notice of suspension of activities. _________________________________________________________________________________________________________________________________________ Page 4 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 7 Obligation for Reporting The owner shall, in designing, constructing and operating the power facilities, report those matters to comply with the technical requirements of Chapter XI of Law on electricity 2018 and any other applicable laws, regulations and agreements including Lao Dam Safety Guidelines and requirements of Article 5. The reports shall include but not limited to pre-feasibility reports, feasibility reports, basic design reports, environmental and social reports, periodic progress and commencement reports, operations and monitoring reports, quality assurance and quality control reports, emergency action plans, inspection report, accident report etc, as applicable to power facilities. 1. (1) Reports concerning the hydropower civil engineering facilities shall be prescribed items below: Pre-feasibility Report/Feasibility Report The owner shall prepare Pre-feasibility and Feasibility reports and submit for approval. (2) Basic Design Report After approval of Pre-feasibility report/Feasibility report, the owner shall prepare Basic design report and submit for approval. (3) Emergency Action Plan for construction In accordance with Article 4, emergency action plan should be prepared and approved inline with the Lao Dam Safety Guidelines for Emergency Action Plan prior to start of construction. (4) Construction commencement report Commencement of construction shall be reported after obtaining approval for construction commencement examination as prescribed in Article 5-1-(1) and before commencement of construction. (5) Report on quality control and assurance for/ during construction of dam Report on quality control and assurance plan before commencement of dam construction and regularly report of the same during course of dam construction shall be regularly reported. (6) Emergency Action Plan for reservoir impoundment In accordance with Article 4, emergency action plan should be prepared and approved inline with the Lao Dam Safety Guidelines for Emergency Action Plan prior to impoundment. (7) Rules of flood management For dams categorized as "High" in Article 17-2, a dam management system, discharge procedure, and measures to mitigate danger to downstream areas in case of flood situations shall be reported prior to the start of first impounding. (8) Report on Reservoir Impoundment Prior to first impounding, inspection of the concerned hydropower civil engineering facilities _________________________________________________________________________________________________________________________________________ Page 5 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) shall be carried out in accordance with Article 5.1.3 of LEPTS and Lao Dam Safety Guideline for Reservoir Impoundment. The details of the inspection shall be reported before commencement of impounding. (9) Emergency Action Plan for operation In accordance with Article 4, emergency action plan should be prepared and approved inline with the Lao Dam Safety Guidelines for Emergency Action Plan prior to operation. (10) Report for commencement of operation After passing the examination before first impounding as prescribed in Article 5-1-(3) and before starting operation, operation commencement shall be reported before operation commencement. (11) Report for Instrumentation and monitoring results The results of regular monitoring as prescribed in Article 23-1 shall be quarterly reported. (12) Report for emergency inspection results The results of emergency inspection as prescribed in Article 23-2 shall be reported. (13) Update and approval of Emergency Action Plan during operation In accordance with Article 4, emergency action plan should be regularly updated and approved inline with the Lao Dam Safety Guidelines for Emergency Action Plan throughout the life of project. (14) Accident report If there arises any serious accident where the principles of the technical standards as shown in Article 1 concerning the hydropower civil engineering facilities are violated, such accident shall be promptly reported. 2. Reports concerning the electrical facilities shall be prescribed items below: (1) Construction commencement report Commencement of construction shall be reported after obtaining approval for construction commencement examination as prescribed in Article 5-2-(1) and before commencement of construction. (2) Report for commencement of operation After passing the examination and inspection as prescribed in Article 5-2-(2), the commencement of operation shall be reported before commencement of operation. (3) Report on commissioning The owner shall report the details of the tests conducted on completion of the construction works that shall comprise the following: _________________________________________________________________________________________________________________________________________ Page 6 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (4) Pre-commissioning tests. Commissioning tests including operational and performance guarantee tests. Trial operation tests including reliability tests for each turbine Generating Unit Accident report If there arises any serious accident where the principles of the technical standards as shown in Article 1 concerning the electrical facilities are violated, such accident shall be promptly reported. _________________________________________________________________________________________________________________________________________ Page 7 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Chapter 2 Article 8 Hydropower Civil Engineering Facilities 2-1 General Definitions The following terms are defined as specified by their relevant paragraph. 1. Dam "Dam" means a barrier, including its foundation and affiliated electric and mechanical facilities, installed to store flowing water or divert it to intakes. 2. Dam body height “Dam body height" means the difference in elevation between the lowest part of the dam body foundation and the crest of the non-overflow section of the dam body. 3. Waterway "Waterway" means channels, tunnels and auxiliaries which convey water from reservoirs to powerhouses for generating, and convey water from power houses to downstream river for water return. Generally, “Waterway” includes intakes, settling basins, headraces, head tanks, surge tanks, penstocks, and tailraces. 4. Reservoir "Reservoir" means flowing water impounded by one or more dams, dike, training dam, or surrounding ground; it also means land on which water is impounded to the highest level. 5. Inflow Design Flood (IDF) “Inflow design flood (IDF)” means the flood that a dam body is capable of safely passing through spillway and withstanding loading condition under normal operation without any damage to the dam. 6. Check Flood “Check Flood” means the flood that a dam body must be capable of withstanding under extreme condition while continuing to operate safely with allowance for some damage and reduction in safety factor without causing breaching of dam. 7. Population at Risk (PAR) “Population at risk “means all those persons directly exposed to floodwaters within dam break affected zone in case no action could be taken to evacuate them. 8. Incremental PLL “Incremental Potential Loss of Life” means difference in estimated potential loss of life for a flood event with dam failure and estimated potential loss of life for the same flood event without dam failure. 9. In the case that a dam or waterway is established as a “low-voltage hydropower electric plant” defined in Article 55, Paragraph 11, and in the case that establishing dam or waterway, operating dam or waterway, and collapsing of dam or waterway may conform with the principles mentioned in Article 1, and in the case that damage by these is limited within the hydropower civil engineering facilities even if it collapses; then the dam or waterway is excluded from these definitions (i.e. it is possible for the dam or waterway not to conform with these technical standards). _________________________________________________________________________________________________________________________________________ Page 8 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2-2 Article 9 Fundamental Requirements Prevention of Overtopping from Non-overflow Sections of Dams All dams shall be designed such that under all operating conditions and in the event of extreme flood conditions, there shall be no overtopping of the non-over flow sections of the dam. Passage of extreme floods shall be via spillways and emergency spillways. The magnitude of extreme flood shall be determined by the hazard rating and failure consequences of the dam. Article 10 Dam Stability All dams shall be designed to be stable under all circumstances including all normal and abnormal operating conditions, including the circumstances of extreme flood and earthquake events such that there shall be no uncontrolled release of water. Article 11 Prevention of Seepage Failure of Dams A dam and its foundations will be subjected to seepage flow from upstream to downstream. The design of the dam shall be such as to limit seepage flows such as to prevent failure modes associated with high seepage rates. Measures shall be introduced into foundations, such as a form of cut-off by grouting or other means, to limit seepage flow and prevent instability of the foundation particularly at the dam toe. Article 12 Prevention of Serious Deformation and Cracking of Dams 1. A dam foundation shall have the required bearing capacity. A fault or weak stratum shall be given appropriate treatment to prevent serious settlement from occurring. 2. Cracking in dams affects the water tightness, internal stresses, durability and appearance and is caused either by imposed loads or by volumetric changes or by both and shall be reduced to acceptable limits by the use of appropriate design and construction procedures. 3. A fill dam body shall be embanked with the materials selected so as to prevent serious settlement or cracking. Article 13 Prevention of Failure of Waterways and Other Facilities 1. A waterway shall be stable against expected loads and shall not be damaged by a landslide or flood. 2. A waterway shall be able to convey and control designed discharge safely and securely and be stable against hydraulic phenomena which are foreseeable. 3. A waterway shall include arrangements to remove sediment particles larger than the permissible size, as specified by turbine manufacturers, from getting carried in the flowing water to the turbine. Arrangement like sediment trap/ desilting basin may be provided to prevent damaging materials reaching the turbine. Article 14 Prevention of Failure of Powerhouses and Other Facilities _________________________________________________________________________________________________________________________________________ Page 9 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Any structure related to hydropower civil engineering facilities, including powerhouses, switchyard, transmission lines, maintenance roads, and temporary facilities for construction etc. shall be stable against the imposition of expected loads and be protected against damage by landslide or flood. The powerhouse shall also be protected against tail water conditions under design floods. Access roads shall remain usable upto the 100 year flood and be undamaged by the design flood. Article 15 Prevention of Seepage Failure of Ground around a Reservoir Establishing a reservoir shall not cause serious water leakage to surrounding ground, seepage failure, or large-scale landslide. Potential large-scale landslide areas should be checked and if required, appropriate protection and monitoring measures be provided. Article 16 Prevention of Damage to Upstream and Downstream Areas 1. Discharge from a dam during a flood shall be ensured so as not to aggravate damage to the downstream area. 2. Appropriate measures shall be taken when there is a possibility that an inundation of properties such as houses at upper reach areas will occur because of the rising water level due to sedimentation. 3. Appropriate measures taken when there is a possibility that damage of the downstream area will occur by rapid change of water level due to the discharge from the tailrace of the hydropower station. 4. Appropriate measures shall be taken so that necessary discharge may be implemented for water utilization and river environment prevention of the affected zone between a dam and a powerhouse. 5. Requirements for environmental mitigation shall be established in an approved environmental and social impact assessment and recommendations shall be incorporated in the project design. 2-3 Dams 2-3-1 Article 17 Common Rules Inflow Design Flood (IDF) Selection Two stage approach for inflow design flood (IDF) selection is set considering project scale and severity of downstream damages along with population at risk. Initial stage selection shall be based on assessment of total risk and its type in accordance to project scale and judgement on foreseen socio-economic environment. Final stage selection shall be based on comprehensive assessment for downstream consequences criteria associated with the flood-induced dam failure and non-failure of dam especially for high and extreme risk category. _________________________________________________________________________________________________________________________________________ Page 10 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 1. Initial stage selection Selection of Inflow Design flood (IDF) and Check flood for a dam shall be set as follows, according to dam classification set in Paragraph 2: 2. SNo. 1 2 Risk Type Low Moderate IDF 100 year 500 year 3 High 1000 year 4 Extreme PMF Check Flood 200 to 500 year 1000 to 5000 year 5000 to 10000 year or PMF --- Dam Classification The criteria for classification of the dams (hazard rating) will be based on the below risk considerations. Hence, for classification of the dams foregoing considerations for risk assessment shall be followed as given in table: SNo. 1 2 T h e c a t 3 4 Risk Factor Storage Capacity (Mm3) Weighting points Height (m) Weighting points Population at Risk (No. of persons) Weighting points Potential Downstream Damage (in terms of impact on economy, society and environment) Weighting points SNo. 1 2 3 4 Low < 0.1 0 < 15 0 Moderate 0.1-3 4 15-30 2 High 3-100 6 30-45 4 Extreme > 100 8 > 45 6 None 1-10 10-100 > 100 0 4 8 12 None Low Moderate High 0 4 8 12 Risk Type Low Moderate High Extreme Total Risk factor 0-6 7-18 19-30 31 -38 Total risk factor can be calculated by following formula as Total Risk Factor = Risk Factor (Capacity) + Risk Factor (Height) + Risk Factor (Evacuation Requirements) + Risk Factor (potential downstream damage) 3. Final stage selection The criteria for final selection of IDF shall be based on comprehensive assessment of downstream consequences under both normal and flood flow conditions. Evaluation of incremental downstream consequences can be initiated with initial stage IDF and extended to check flood in the event of dam failure and non-failure of dam. Detailed studies including dam break analysis shall be required to evaluate river reach and areas affected by a dam failure for downstream consequence assessment. Special considerations for selection of dam breach _________________________________________________________________________________________________________________________________________ Page 11 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) parameters shall be required for realistic assumption depending on the type of dam and factors affecting the failure mechanism like size and shape of the breach, time of breach formation, hydraulic head, storage in the reservoir and reservoir inflow. Downstream consequences shall be determined by estimation of incremental losses either in terms of Population at risk (PAR) or incremental potential loss of life (PLL).Potential incremental losses shall also be assessed with respect to property downstream or other areas influenced by the dam. Engineering judgement and sensitivity analysis are needed to make final selection of acceptability of consequences and according selection of appropriate IDF. After consequence based assessment, suitable measures should be adopted to keep the hazard potential within acceptable limits. For evaluation of consequences, reservoir operating conditions shall be followed subjected to the condition that reservoir is at normal maximum pool elevation at the time of impingement of flood hydrographs to the reservoir. Possible future development in downstream shall also be kept under consideration while evaluating incremental consequences. 4. Cascade Development In cascade development, if two or more dams are located on the same river, new dam shall be designed for peak obtained by considering the floods passing through upstream dam spillway coupled with local inflow flood of sub catchment in between the dams. In case, dams are located on two rivers upstream of its confluence, new dam downstream of confluence shall be designed for resulting flood peak obtained at the confluence due to routed flood peak from dams on both tributaries of river coupled with local inflow flood of sub catchment between the downstream dam and the confluence of two tributaries. Appropriate IDF for new dam shall be selected after assessment of incremental consequences downstream in case of failure and non-failure of upstream dam. 5. Construction Diversion Flood Adoption of diversion flood return period shall be governed by acceptable risk during the period of construction. Incomplete concrete dams can pass floods without appreciable damage. Lower return period varying from 1 in 10 to 1 in 25 year may be adopted based on frequency analysis of yearly maximum non-monsoon peak. In case of fill dams, passage of flood on incomplete fill dam is unacceptable and passage may be left in river course for passing the monsoon floods. Alternatively, diversion flood of higher return period should be adopted for fill dams from annual and seasonal flood peaks based on provision of adequate flood diversion arrangement with acceptable risk. For projects on small rivers lacking historical flood records, diversion discharge of return period equivalent to 5 to 10 times of construction period may be adopted as diversion flood at construction stage. Article 18 Basic Water Levels Basic water level, on which the specifications of a dam are to be determined, shall be set as follows: 1. Normal water level shall be the highest level of water stored in the reservoir of a dam during a non-flood period. 2. Flood water level shall be the highest water level when the inflow design flood passes over the spillway particularly for run-off-river schemes with minor/negligible storage capacity In case , storage effect of the reservoir is significant, flood water level shall be the highest water level attained during reservoir routing of inflow design flood (IDF) hydrograph through ungated or gated spillway with a gate jammed shut subjected to condition that IDF impinges the reservoir _________________________________________________________________________________________________________________________________________ Page 12 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) at normal maximum pool elevation. 3. Low water level shall be the lowest level of water stored in the reservoir of a dam under normal reservoir operation. 4. Dead storage level shall be the level of reservoir occupied either by progressive deposition of incoming sediment loads or remains unutilized for any useful purpose throughout service life of the reservoir. Article 19 Freeboard The non-overflow portion of the dam body shall satisfy the following: 1. The non-overflow portion of the dam body shall be higher than both the normal water level plus the freeboard and the flood water level plus the freeboard. Freeboard shall be set separately for flood water level and normal water level by considering the type of dam, wind-induced waves, earthquake-induced waves, and presence or non-presence of a spillway gate. (1) Freeboard for normal water level (normal freeboard) hw + he + ha + hi and yet 2 m or higher (2) Freeboard for flood water level (minimum freeboard) hw + ha + hi and yet 1 m or higher (3) freeboard for flood water level (Check flood) hw + ha + hi and yet 0.5 m or higher where hw : the wave height caused by wind he : the wave height caused by earthquake. ha : 0.5 m if the dam has a spillway gate and 0 m if it does not hi : 1 m for a fill dam and 0 m for a concrete dam (Inflow Design Flood) 0.5 m for a fill dam and 0 m for a concrete dam (Check flood) In case of reservoirs with significant storage effect, the reservoir water levels shall be determined by conducting flood routing studies for inflow design flood and check flood. For a high degree of protection, during routing of applicable flood, sensitivity of the stipulation with a gate assumed jammed, be studied. In the case of reservoirs with large surface areas, the change in water level might be small, whereas for reservoirs with small surface areas, loosing outflow capacity can lead to overtopping of the dam. As, this factor is site specific and therefore, effect of loss of spillway capacity, if any shall be based on the sensitivity of the results of the flood routing studies. Wave conditions due to severe reasonable wind conditions shall be used. In the case of a fill dam, both the normal water level and the flood water level shall be equal to or lower than the crest of the impervious core. Additional freeboard or provision for overtopping may be required for dams on reservoirs subject to landslide induced waves. _________________________________________________________________________________________________________________________________________ Page 13 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 20 Loads 1. The loads which shall be considered in the case of design of dam body shall be defined in the table below. Table 20-1: Loads imposed on dam bodies Type of dam Loads Gravity dam Self-weight, hydrostatic pressure, hydrodynamic pressure, mud pressure, seismic forces uplift and temperature load Arch dam Self-weight, hydrostatic pressure, hydrodynamic pressure, mud pressure, seismic forces, uplift and temperature load Fill dam Self-weight, hydrostatic pressure, seismic forces and pore pressure 2. Pore pressure and uplift (1) Pore pressure for a fill dam and its foundation shall be determined by considering the permeability of the materials used for the dam body drainage, and based on calculations, tests and experience through actual measurements of seepage flow. (2) Uplift on a concrete gravity dam shall be determined assuming a linear pressure distribution based on head pond level, tail water level and drainage curtain efficiency. 3. Seismic force There are few earthquakes in Lao and, therefore, there are no seismometers and seismic records. Severe earthquake zone exists in the northern part, whereas the central part and southern parts have small danger of earthquakes. Lao has been divided into four seismic zones and these are shown in the below figure. The estimated seismic coefficients for different zones are presented in Table 20-1, for different types of dams. (1) Seismic force acting on the dam body shall be deemed as acting horizontally and vertically-vertical to be taken as two-third of horizontal. Seismic force need not be considered in the structural analysis in the case of extreme flood conditions. (2) In the case of severe and middle seismic zones as shown in the Lao country seismic zone map, site specific seismic assessment shall be conducted. Site-dependent earthquake assessment study shall be carried out through a specialized institute for the purpose. The study shall include dynamic analysis of dam and associated structures depending on the hazard category and type of the dam. _________________________________________________________________________________________________________________________________________ Page 14 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 20-2: Estimated Seismic coefficients (PGA for MCE condition) Zones Severe Middle Moderate Minor Article 21 Gravity Dam 0.15 0.15 0.1 0.07 Arch Dam 0.24 0.24 0.2 0.12 Fill Dam Homogeneous Dam (Earth-fill dam) 0.15 0.15 0.12 0.1 Rock-fill dam 0.15 0.15 0.1 0.1 Dam Foundations A dam foundation shall satisfy the following: 1. A dam foundation including abutments shall be put to appropriate geologic investigation, permeability tests and strength tests depending on the dam size. 2. A dam foundation shall have required bearing capacity/ uniaxial compressive strength and shearing strength, and shall not have serious settlement, serious cracks, sliding failure and serious erosion. 3. Appropriate countermeasures such as grouting or drainage shall be taken at the dam foundation and at the abutments, when warranted in order to limit excessive uplift, serious water leakage or seepage failure. 4. Any fault or other weak stratum in the foundation shall be given appropriate treatment as necessary so that the foundation possesses the required strength and water-tightness. Article 22 Prevention of Serious Water Leakage from Dams _________________________________________________________________________________________________________________________________________ Page 15 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The dam body and the contact areas between the dam body and its foundation shall be such that serious water leakage does not occur, as water leakage can affect stability of the dam or result in progressive deterioration. In a concrete dam, grout curtains and drainage holes shall be provided through a foundation gallery in the dam near the upstream face. In earth and rockfill dams depending on the foundation strata, either grout curtain or a cut off upto rock foundation shall be provided below the clay core. Article 23 Monitoring and Inspections 1. In principle, in the case that the dam body height is 15 metres or more, or in the case that the type of the dam is special, or in the case that the permeability of the dam foundation before taking countermeasures is high, or in the case that there is a large weak stratum, of the foundation, with insufficient strength before taking countermeasures, in order to confirm the safety and proper functioning of a dam body, and proper functioning of a reservoir, monitoring equipment shall be established and regular monitoring shall be implemented depending on the conditions of the safety of the dam body , the progress of sedimentation of the reservoir and in line with the Lao Dam Safety Guidelines. (1) In the case of a concrete dam, volume of water leakage, deformation, displacement between dam blocks and sedimentation shall be monitored (2) In the case of a fill dam, volume of water leakage, deformation, permeation line of a homogeneous fill dam, and sedimentation shall be monitored 2. In the case that abnormal loads such as earthquake or flood occur, an emergency inspection shall be implemented as per Guidelines for Dam Safety immediately in order to confirm the safety and proper functioning of the dam. The inspection items shall be volume of water leakage from the dam and around the reservoir, uplift of the concrete dam, deformation, permeation line of the homogeneous fill dam, the proper functioning of the spillway gates, and so on. 3. In principle, in the case that the dam body height is 15 metres or more, or in the case that the type of the dam is special, or in the case that the permeability of the dam foundation before taking countermeasures is high, or in the case that there is a large weak stratum, of the foundation, with insufficient strength before taking countermeasures, it is desirable to have an established gallery in accordance with necessity for inspections and repairs. 2-3-2 Article 24 uplift, Concrete Dams Concrete Materials Concrete materials used for a dam shall be in accordance to standards published by ASTM. Article 25 Foundations for Concrete Dams The foundation for a concrete dam shall satisfy the following: 1. The shear strength, internal friction coefficient and modulus of deformation shall be determined by the results of in-situ tests in principle, as per the procedures laid down in Lao Dam Safety Guidelines- Geological and Geotechnical and taking into consideration the geology of the foundation. In principle, in the case that the dam body height is less than 15 metres, site specific geological mapping followed by geophysical survey may give adequate information’s of sub surface configuration below the dam foundation. Additionally, dam foundation must be _________________________________________________________________________________________________________________________________________ Page 16 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) investigated through at least three exploratory drill holes upto a minimum depth of 30 m if bedrock is not encountered or 10 m into the acceptable foundation grade bedrock. In conducting an in-situ test, representative points hat are appropriate for determining the foundation properties of the dam shall be selected based on careful consideration of the geology of the dam foundation. 2. Grouting (1) Consolidation grouting involves area grouting for a shallow depth and shall be done in the foundation to improve existing defects, and mechanical properties of rock mass such as to improve the deformation characteristics and bearing capacity of the rock strata, utilizing holes arranged in a pattern or grid. Consolidation grouting is generally done before concrete placement. (2) It is possible to achieve post grouting permeability even less than 1 lugeon, depending on the sophistication of grouting programme. The efficacy of the grouting operation shall be tested by pre and post grouting permeability of the foundation measured with percolation tests. Acceptable permeability depends on the height of the dam limiting to maximum lugeon value upto 5 for medium dams and limiting to a value of around 3 lugeons for high dams. Lugeon value represents hydraulic conductivity as well as the rock joint pattern. A value less than 5 represents low conductivity and tight rock discontinuity condition, whereas less than 1 denotes very low conductivity and very tight rock discontinuity condition. (3) Curtain grouting shall be performed near the upstream face of the dam, to reduce permeability by constructing a curtain or barrier of grout. Therefore, it acts as a seepage cut-off under a dam. Curtain grouting is commonly done after concrete has been placed to a considerable height or even after the structure has been completed. (4) Depth, spacing and orientation of grout holes should be related to the geological feature and water head. (5) Target Lugeon values need to be based on the requirements of design and can vary throughout the depth of a grout curtain. (6) Depth of grout curtain shall be determined based on comprehensive considerations of seepage analysis, geological conditions, uplift pressure etc. and is selected on the basis of reservoir water depth. 3. A line of drainage holes is drilled at a distance downstream from the grout curtain, to collect seepage water and reduce uplift pressures under the dam and its base, to permissible design values. Article 26 Stability of Concrete Gravity Dams A concrete gravity dam shall satisfy the following: 1. The dam body shall be stable with respect to overturning due to cracking. Under usual operation, the application centre of resulting force of the expected external force and the self-weight shall be within the centre one-third (i.e. the middle third) of the horizontal section of the dam body. In the case of earthquake or flood, it shall be within the centre one-second (i.e. the middle half) of the horizontal section of the dam body. 2. The dam body, the contact area between the dam body and the foundation, and any weak stratum of the foundation shall be stable with respect to sliding. Sliding stability shall be checked along any plane or combination of planes within the dam, at the contact plane with foundation or along joints within the foundation. _________________________________________________________________________________________________________________________________________ Page 17 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (1) The factor of safety against sliding calculated by the following formula shall be three or more under usual conditions (the water level of the reservoir is between the normal water level and the low water level. It shall be two or more in the case of an earthquake or flood. n = (f v + c l)/H where n: f: c: Factor of safety against sliding Internal friction coefficient cohesion (N/m2) v: Total vertical force acting on the shear plane per unit width (N) H: Total horizontal force acting on the shear plane per unit width (N) l: Area resisting with respect to the shear force per unit width(m2) For final designs, values of internal friction coefficient and cohesion used in the equation, shall be determined by actual laboratory and field tests and taking into account the strength of discontinuities in the foundation. Dams with irregular geometries or complex foundations or spillway sections with long aprons, shall be analyzed with advanced methods like Finite Element Method (FEM), taking into account the uplift pressures as body forces and the foundation interaction also. (2) If the dam body height is less than 15 metres and cohesion of the foundation is not taken into account, the factor of safety against sliding shall be maintained at 1.5 or more under normal conditions and 1.2 or more in the case of an earthquake or flood. 3. Stress Analysis The magnitude and distribution of stresses throughout the dam structure shall be determined for static and dynamic load conditions. The stresses on the upstream and downstream faces of a concrete gravity dam are calculated by the equations using gravity method of analysis. For high dams or medium dams on complicated foundations or dams with large openings, finite element method (FEM) of stress analysis shall be conducted. Two-dimensional FEM analysis is generally appropriate for gravity dams. Stress inside the dam body shall not exceed the allowable stress as described below. (1) The allowable compressive stress of concrete shall be one third of the compressive strength. It shall be one half of the compressive strength in the case of an earthquake or flood. (2) The allowable tensile stress of concrete shall be one fortieth of the compressive strength except for usual loading condition. No tensile stress shall be permitted at the upstream face under usual loading condition. Local areas of tension on the downstream face may be accepted. (3) The specific age of the concrete that should be used for the strength test shall be 91 days in principle. It shall be determined by considering the time lapse from the time point of concrete placing to that of loading. (4) The proportioning strength of concrete shall be decided with the additional rate which shall be considered in terms of variance of compressive strength to the required compressive strength as follows: _________________________________________________________________________________________________________________________________________ Page 18 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (The proportioning strength) = (The required compressive strength) × (The additional rate of variance of compressive strength) However, statistical distribution of concrete strength based on laboratory test results of samples shall be used for the design. In the case of earthquake, static analyses using the appropriate design seismic coefficient shall be implemented in principle. In the case of severe to moderate seismic zones as shown in the Lao country seismic zone map, site specific seismic parameter study shall be conducted. Dynamic analysis using site-specific earthquake ground motions shall be considered necessary in accordance with relevant guidelines stipulated in ICOLD or equivalent international acceptable guidelines. Article 27 Stability of Arch Dams Arch dams shall satisfy the following: 1. The contact area between the dam body and the foundation and any part of the foundation shall be stable with respect to sliding. The factor of safety against sliding calculated by the following formula shall be four or more under usual conditions (the water level of the reservoir is between the normal water level and the low water level). It shall be 2.7 or more in the case of an earthquake or flood. n = (f v + c l)/H where n: Factor of safety against sliding f: Internal friction coefficient c: (N/m2) v: Total vertical force acting on the shear plane per unit width (N) H: Total horizontal force acting on the shear plane per unit width (N) l: Area resisting with respect to the shear force per unit width(m2) For Final designs, values of internal friction coefficient and cohesion used in the formula, shall be determined by actual laboratory and field tests using standard procedures in Lao Dam Safety Guidelines and taking into account the strength of the discontinuities in the foundation. 2. Stress inside the dam body shall not exceed the allowable stress as described below. (1) The allowable compressive stress of concrete shall be one third of the compressive strength. It shall be one half of the compressive strength in the case of an earthquake or flood. (2) The allowable tensile stress of concrete shall be one fortieth of the compressive strength, except for usual loading condition. No tensile stress shall be permitted at the upstream face under usual loading condition. Tensile stresses shall be avoided by re-design. Local areas of tension on the downstream face may be accepted. (3) The specific age of the concrete that should be used for the strength test shall be 91 days in _________________________________________________________________________________________________________________________________________ Page 19 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) principle. It shall be determined by considering the time lapse from the time point of concrete placing to that of loading. (4) The proportioning strength of concrete shall be decided with the additional rate which shall be considered in terms of variance of compressive strength to the required compressive strength as follows: (The proportioning strength)= (The required compressive strength) × (The additional rate of variance of compressive strength) However, statistical distribution of concrete strength based on laboratory test results of samples shall be used for the design. In the case of earthquake, static analyses using the appropriate design seismic coefficient shall be implemented In the case of severe and moderate seismic zones as shown in the Lao country seismic zone map, site specific seismic parameter study shall be conducted. Dynamic analysis using site-specific earthquake ground motions shall be considered necessary in accordance with relevant guidelines stipulated in ICOLD or equivalent international acceptable guidelines. Article 28 Structural Details of Concrete Dam Body A concrete dam body shall satisfy the following: 1. Appropriate contraction joints in gravity dam shall be constructed to prevent detrimental cracks. 2. Drainage holes shall be installed as necessary at the gallery to reduce uplift that acts on the dam body, acts on the contact area between the dam body and the foundation, and/or acts on the inside of the foundation. 3. The area surrounding the openings, such as galleries, water discharge equipment or penstocks installed inside the dam body, shall be structurally safe with respect to stress concentration and stress caused by temperature change. 4. Water stops shall have water-tightness and durability, and shall be able to follow stretching of the joints. They shall be installed near and upstream of transverse joints. 5. Galleries shall be provided in the dam as described below: (1) Foundation gallery: used for drainage, drilling drainage holes and grouting and also used for inspection. (2) Downstream drainage gallery at about 2/3 of base width, in the case of high dam, if required (3) Intermediate inspection gallery/s: provided above foundation gallery in the case of high dams. (4) Other galleries such as gate gallery, instrumentation gallery, elevator tower etc. shall be provided as required Article 29 Temperature Regulation for Concrete Dam Body The concrete placement temperature shall be controlled so as to minimize and/or control the size and spacing of cracks in the concrete. The measures and degree of temperature _________________________________________________________________________________________________________________________________________ Page 20 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) control shall be determined by conducting thermal studies of the structure taking into account method of construction and its temperature environment. 2-3-3 Article 30 Fill Dams Embankment Materials Any embankment material shall satisfy the following: 1. Materials possessing properties conforming to the respective purposes shall be used as dam body materials. (1) Of impervious materials, soil materials shall comply with the following: a. Soil materials shall have adequate strength and water-tightness for dam stability. b. Soil materials shall be easily compacted and subject to little deformation. c. Soil materials shall be free of expandability or shrinkage that may cause problems to dam stability. d. Soil materials shall not be prone to softening. e. Soil materials shall contain no organic matter and shall not be water-solvent. f. The coefficient of permeability, strength, and compaction characteristics shall be identified from the actual materials to be used. (2) Of impervious materials, those other than soil ones shall be identified to have the required water-tightness, strength and durability from the actual materials to be used. (3) Semi-pervious materials shall comply with the following: (4) (5) a. Semi-pervious materials shall have adequate strength and drainage properties for dam stability. b. Semi-pervious materials shall have the required grain size distribution. c. Semi-pervious materials shall be easily compacted and subject to little deformation. d. The coefficient of permeability, strength, and unit weight shall be identified from the actual materials to be used. Pervious materials shall comply with the following: a. Pervious materials for dam stability; shall have adequate strength and drainage properties b. Pervious materials shall be hard and durable; c. Pervious materials shall be easily compacted and subject to little deformation, and d. The coefficient of permeability, strength, unit weight, and durability shall be identified from the actual materials to be used. Materials used for the surface of the dam body shall not be seriously eroded by waves or _________________________________________________________________________________________________________________________________________ Page 21 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) rainfall. 2. When materials are selected, they shall be given appropriate tests to identify their characteristics before actual use. When the strength of any selected material is determined as part of the process of stability calculation, its consolidation and drainage conditions shall be considered in setting the strength. Article 31 Foundations for Fill Dams Dam foundations of a fill dam shall satisfy the following: 1. Foundations of impervious zones require hard rock foundations and shall have adequate water-tightness and strength; 2. In the case of foundations other than rock, the water-tightness, strength and deformation shall be investigated through in-situ and laboratory tests. Safety against liquefaction in case of an earthquake shall also be ensured; 3. Sand-gravel foundations shall require countermeasures to be taken as necessary in order to secure adequate stability against seepage and deformation; 4. Soil foundations shall require countermeasures to be taken as necessary in order to secure adequate stability against sliding and deformation; 5. Curtain grouting is recommended for control of seepage. The grout curtain shall be of adequate depth and spacing to achieve the required permeability within the grouted zone. Acceptable limit of permeability may be less than 5 lugeons, as higher values may correspond to rock with few partly open discontinuities. Spacing and orientation of grout holes shall be based on the geological conditions such as spacing of joints in the foundation. The location of the curtain shall be at/ or upstream of the dam centreline. The design depth depends on the geology, regional groundwater conditions, permeability and generally shall extend 0.5 to 1.0 times the reservoir head. For various other considerations, reference may also be made to Guidelines for Dam Safety- Geological and Geotechnical. Blanket grouting is recommended for permeable foundations. Large zones of fractured and jointed rocks shall be treated by blanket grouting up to sufficient depth beneath the clay core at the contact of the core and foundation. Article 32 Stability of Fill Dams A fill dam shall satisfy the following: 1. A dam body and its foundation shall be stable with respect to sliding. The analyses against sliding shall be reliable circular arc methods (in principle Spencer’s method). In the case that sliding lines, which include the foundation, and so on are expected, the calculations along the sliding lines, not only circular, shall be implemented. Required safety factors shall be the following: (1) Safety factor shall be 1.5 or more under usual conditions (the water level of the reservoir is between the normal water level and the low water level, and the seepage flow in the dam is in steady state); (2) Safety factor shall be 1.4 or more in the case of flood; (3) Safety factor shall be 1.3 or more in the case of being just after completion and before filling; (4) Safety factor shall be 1.3 or more in the case of rapid draw down if frequent draw down of the reservoir is implemented, and _________________________________________________________________________________________________________________________________________ Page 22 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (5) Safety factor shall be 1.1 or more in the case of earthquake. 2. In the case of earthquake, static analyses shall be implemented using the appropriate design seismic coefficient in principle. (1) For embankment located in high seismic areas, dynamic analysis shall be performed for assessment of liquefaction potential of susceptible materials in the dam and foundation, determination of permanent deformations that will affect the freeboard of the dam. Dynamic analysis using site-specific earthquake ground motions shall be considered necessary in accordance with relevant guidelines stipulated in ICOLD or equivalent international acceptable guidelines. Article 33 Restrictions on Facilities such as Discharge Facilities Discharge facilities or waterways which have a possibility of cracks occurring inside the dam body shall not be constructed inside the dam body. For embankment dams, pipes or conduits shall not pass through the dam body. Article 34 Design for Homogeneous Type Fill Dams For homogenous type dams constructed with impervious materials, the seepage line shall not appear on the slope of the downstream part of the dam. Appropriate drainage shall be installed as necessary to promote control of pore pressure. Homogeneous fill dams shall only be adopted for dams of low hazard rating and less than 15m high. Article 35 Design for Zoned Type Fill Dams For zoned type dams, zones shall be appropriately allocated. Materials of these zones in contact with each other shall not be too much different in order that movement of material particles in each zone does not occur. Materials for these zones shall comply with appropriate filter relationship. Article 36 Design for Surface Diaphragm Type Fill Dams A surface diaphragm type fill dam shall satisfy the following: 1. An upstream membrane or concrete faced fill dam shall be designed so that if leakage through the upstream face occurs the internal design of the fill zones shall safely manage the seepage flows. 2. Appropriate water sealing countermeasures shall be taken, depending on the permeability of the foundation, to prevent seepage failure at the foundation. 2-3-4 Article 37 Other Types of Dams Other Types of Dams Other dams such as rubber dams and gabion dams (those other than a fill dam, a concrete dam or a concrete arch dam) shall be installed in accordance with the following: 1. Safety against expected events, such as overturning, sliding, occurrence of excessive stress on materials used, cracking, or seepage failure, shall be sufficiently considered in designing dams. _________________________________________________________________________________________________________________________________________ Page 23 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2. In case materials other than soil, rock, or concrete are used, the materials shall be tested to fully identify their durability, water-tightness and strength. Concrete materials shall satisfy Article 24. Soil and rock materials shall satisfy Article 30. 3. For other types of dams, such as concrete faced rock fill dam, roller compacted concrete dam, cemented materials dam etc., recommendations in relevant ICOLD Bulletins shall be adopted. 2-3-5 Article 38 Spillways and Other Discharge Facilities Spillways A spillway shall satisfy the following: 1. The spillway should be sized to safely pass inflow design flood (IDF) without placing the safety of the dam at risk. 2. For a fill dam, no spillways shall be constructed on/in the dam body. 3. The bottoms of structures such as bridges or hoisted gate leafs shall be sufficiently apart from the overflowing water surface of the water discharged from the spillway at the flood water level in order that the overflowing water which is discharged from the spillway at the flood water level flows safely. 4. The force of water flowing through/down the spillway shall be buffered by providing suitable energy dissipation arrangement to prevent negative impacts on the dam body and the downstream areas. Plunge pools and other areas near the dam toe shall be designed such that no significant damage occurs under design flood conditions. 5. A spillway shall have the stability prescribed in Article 26 or 27 with respect to loads as provided for by the applicable specifications for concrete gravity dams and the loads to be generated during the down-flow of water discharged from the spillway at the flood water level. 6. Reliable calculation methods shall be used in designing spillways or discharge facilities. Hydraulic design using standard method shall be done for spillway and energy dissipation arrangement. In case calculations alone are not sufficient to produce satisfactory results, hydraulic model tests shall be conducted to verify spillway discharge capacity, spillway geometric profile, and energy dissipation pattern and risk to critical infrastructure. Article 39 Spillway Gates and Auxiliaries A spillway gate and any auxiliaries shall satisfy the following: 1. A spillway gate, as defined herein including a valve and any auxiliaries, shall be water-tight and durable. 2. A spillway gate and any auxiliaries shall be designed to be opened and closed easily and their operation shall not generate any dangerous vibration; 3. A spillway gate and any auxiliaries shall be stable and there shall be no occurrence of buckling against self-weight, hydrostatic pressure, hydrodynamic pressure, mud pressure, seismic force, buoyancy and forces caused by opening and closing. A spillway gate shall be the structure which conveys the imposed loads to the dam body and so on safely; _________________________________________________________________________________________________________________________________________ Page 24 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 4. Materials used for a spillway gate and any auxiliaries shall be confirmed to have necessary strength by the tests which are specified in international standard, or they shall be materials as specified in an international standard which specify necessary strength, 5. In the case that a power-drive device is used to operate the spillway gate an alternative manual arrangement may be considered. Along with the power-drive device, aback-up device shall be installed to ensure gate operation. A 100% independent back-up power supply shall also be provided. The back-up power supply shall be a facility located at the dam that does not rely on grid connectivity or any other form of external power supply. 6. The spillway gates and hoist systems shall be designed by including appropriate seismic load conditions. Article 40 Other Discharge Facilities Other discharge facilities shall satisfy the following: 1. A discharge facility shall be installed in order to decrease the water level of the reservoir at emergency times or to discharge to the affected zone between the dam and the powerhouse. If a water use outlet or a spillway already has this function, such a discharge facility is not required. 2. In case discharge facilities are not usually used, periodic operation checks shall be conducted to ensure proper gate operation. 3. Bottom/Low level Outlets: Opening/s at a low level and at a suitable location vis-à-vis the hydropower intake on the dam, may be used for scouring of sediment, after confirmation of its performance on mathematical and physical model. Bottom outlets can also be used for Lao dam safety considerations. Such provision in dam facilitates to (i) reduce reservoir loads in an emergency situation (ii) inspect and repair dam components following a natural disaster,(iii) inspect and repair deficiencies resulting from aging and deterioration. Low level outlets may be decided in such a way that it is placed as low level as possible and with adequate capacity to allow controlled drawdown during emergency. Assessment of downstream impact of outflow needs to be evaluated during its operation. 4. Dams shall be capable of lowering the reservoir water level with required drawdown rates within a reasonable time period considering the type of dams and the downstream hazards. 2-4 Article 41 Waterways Common Rules A waterway shall satisfy the following: 1. A waterway shall not be damaged by a flood, land sliding and so on; 2. Construction of a waterway shall not cause serious water leakage, landslides, or any other detrimental consequences; 3. A waterway shall not be significantly damaged by driftwood, floating debris, or sediments which flow into the waterway; 4. A waterway shall be able to safely by-pass the excess volume of water if water in excess of the designed discharge flows into the waterway; _________________________________________________________________________________________________________________________________________ Page 25 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 5. A waterway shall be provided with appropriate access for inspection and maintenance works. Safe double isolation from the reservoir end also shall be provided. 6. The concrete to be used for a waterway shall satisfy Article 24. Steel materials to be used for a waterway shall be confirmed to have necessary strength by the tests which are specified in a standard such as ASTM, or they shall be materials as specified in a standard such as ASTM which specify necessary strength. Other materials to be used for a waterway shall be confirmed that they shall have required strength and durability. 7. The waterway shall safely withstand worst transient pressures, and also de-watering condition. Transient pressures shall be estimated by conducting mathematical model hydraulic transient studies of the complete water conveyance system between reservoir and tailrace. Article 42 Intakes An intake shall satisfy the following: 1. An intake shall be stable with respect to self-weight, hydrostatic pressure, hydrodynamic pressure, mud pressure, seismic force, external water pressure and earth pressure; 2. A downstream sealing stop log and upstream sealing service gate shall be provided to permit double isolation for maintenance works. 3. The service gate shall be designed for partial gate operation and throttling to regulate the discharge. 4. A location and structure of an intake shall be designed to prevent inflowing sediment, debris, garbage and so on and the design of the intake shall be selected such that trash or air entraining vortices (Vortex Types 4 & 5) do not form under any service conditions. 5. In the case that an intake is connected to pressure conduits of a headrace or penstock, the location and structure of the intake shall be designed to prevent air intrusion to the pressure conduits, the penstocks or the turbines. Article 43 Settling Basins A settling basin shall satisfy the following: 1. A settling basin shall be stable with respect to self-weight, hydrostatic pressure, hydrodynamic pressure, seismic force, external water pressure and earth pressure; 2. A settling basin shall have the capacity damage a downstream waterway or a turbine, 3. A settling basin shall have the structure in which accumulated sediment can be flushed easily. 4. If standard design and calculations are not sufficient, the performance of settling basin may be verified by conducting physical model studies, to confirm the theoretical calculations. Article 44 to be able to settle sediments which Headraces A headrace shall satisfy the following: _________________________________________________________________________________________________________________________________________ Page 26 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 1. A headrace shall be stable with respect to self-weight, hydrostatic pressure, internal water pressure, external water pressure, seismic force, earth pressure and surcharge; 2. Any leakage from or other structures; 3. A headrace shall not significantly cause damage to the downstream waterway or a turbine due to silting of the waterway; 4. In the case of a pressure and non-pressure conduit, countermeasures such as lining, ground support shall be taken to prevent cave-in of surrounding ground The alignment shall be selected in such a way that minimum ground stress in any direction along the alignment shall be at least 1.3 times greater than the static internal water pressure. Steel lining to withstand the maximum internal transient water pressure shall be provided wherever this criteria is not achieved. 5. A headrace shall be designed such that air entrainment into the headrace tunnel shall not occur under any service conditions. Article 45 1. inside a headrace shall not damage the surrounding ground Surge Tanks and Head Tanks A surge tank shall satisfy the following: (1) A surge tank shall be stable with respect to self-weight, internal water pressure, seismic force, external water pressure, earth pressure and force caused by wind, if applicable; (2) The fluctuation of the water level in the surge tank shall not accelerate and return to equilibrium in a short period. The minimum area of surge tank shall satisfy Thoma criteria and; (3) The upper and lower levels of the surge chamber shall be designed to accommodate the most adverse combination of load acceptance and rejection by the generating plant and reservoir levels, whilst preserving adequate freeboard. The sizing criteria are: adequate freeboard at the top of the tank to prevent overtopping on upsurge; and adequate freeboard at the base of the tank to prevent vortex formation on down surge. 2. A head tank shall satisfy the following: (1) A head tank shall be stable with respect to self-weight, internal water pressure, seismic force, external water pressure and earth pressure and force caused by wind, if applicable (2) When a head tank is operating normally or even if loads increase rapidly, a head tank shall have an adequate water capacity to be able to operate safely so that penstock does not inhale air; (3) A head tank shall have a spillway so that it can control maximum designed discharge safely when the full load is shut off. Notwithstanding the preceding, if facilities other than the spillway have functions to safely control spillage, this may not apply; (4) The increase of water level, when the spillage overflows, shall not cause damage to the headrace; (5) A spillway or a spillway channel shall be designed so that discharge from the spillway or the spillway channel does not cause damage to surrounding facilities or the river utilization; (6) The structures of a head tank shall be designed in order that garbage or sand does not flow _________________________________________________________________________________________________________________________________________ Page 27 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) into a penstock or a turbine, and the accumulated sediment can be flushed easily, and; (7) Mathematical model hydraulic transient studies for the complete water conveyance system shall be conducted for specified loading conditions, to verify the adequacy of tank capacity, with reference to maximum and minimum water levels. Article 46 Penstocks A penstock shall satisfy the following: 1. A penstock shall be stable with respect to loads in accordance with the following types of penstock. Type Loads Exposed type Table 46-1: Loads imposed on penstocks Rock-embedded Earth-embedded type type Composite maximum water pressure of hydrostatic pressure, water hammer pressure and pressure rise by surging; self-weight of pipe, temperature loads, external pressure, water weight in pipe, seismic force and forces of flowing water inside the pipe Composite maximum water pressure of hydrostatic pressure, water hammer pressure and pressure rise by surging; temperature loads and external pressure Composite maximum water pressure of hydrostatic pressure, water hammer pressure and pressure rise by surging; earth pressure, surcharge loads, temperature loads, external loads and water weight in pipe 2. Water hammer pressure shall be calculated on the basis of hydraulic transient studies for extreme load condition. For the rock embedded type, sharing of internal load with the surrounding rock may only be permitted if the CECT Recommendations are satisfied. 3. The crown of a penstock shall be placed below the lowest hydraulic gradient line when the water level of the head tank or the surge tank is at its lowest point. 4. The vertical alignment of a penstock shall be selected to avoid negative pressures and risk of water column separation under all conditions. 5. A pipe shell shall be stable with respect to vibration, buckling and erosion. 6. A penstock shall be designed and constructed to be entirely without any water leakage. 7. In the case of exposed type penstocks, anchor blocks or saddles shall be installed in order to support the penstock pipe shells. An anchor block or saddle shall be stable with respect to the possible anticipated loads of self-weight, self-weight of pipe, water weight in pipe, seismic force, forces of flowing water inside the pipe, surcharge loads and temperature loads. The supporting part of a saddle shall be structured so that the pipe shell can move smoothly as the pipe shell contracts and expands. 8. Resonant water hammer shall considered when assessing extreme internal loading. Alternatively a resonance suppression device may be considered. Article 47 Tailraces A tailrace shall satisfy the following in case it acts like a pressure conduit: _________________________________________________________________________________________________________________________________________ Page 28 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 1. A tailrace shall be stable with respect to self-weight, hydrostatic pressure, internal water pressure, external water pressure, seismic force, earth pressure and surcharge; 2. Any leakage from inside the tailrace shall not damage the surrounding ground or other structures; 3. A tailrace shall not significantly cause damage to the downstream waterway due to the waterway; 4. In the case of a pressure and non-pressure conduit, countermeasures such as lining, ground support shall be taken to prevent cave-in of surrounding ground. The alignment shall be selected in such a way that minimum ground stress in any direction along the alignment shall be at least 1.3 times greater than the static internal water pressure. Steel lining to withstand the maximum internal transient water pressure shall be provided wherever this criteria is not achieved. 5. In the case that a surge tank is installed at the pressure tailrace, it shall be installed as provided for in Article 45, Paragraph 1. Article 48 silting of Gates, Valves, and Auxiliaries A gate, valve and any auxiliaries shall satisfy the following: 1. A gate, valve and any auxiliaries shall be stable with respect to self-weight, hydrostatic pressure, hydrodynamic pressure, seismic force and buoyancy which are anticipated to impose on them; 2. A gate, valve and any auxiliaries shall be water tight; 3. A gate, valve and any auxiliaries shall be able to open and close easily; 4. A gate, valve and any auxiliaries shall have no dangerous vibration upon opening or closing of the gate and the valve; 5. The structural member of gate shall be subjected to structural bending under various loading condition. The deflection of member and stresses within structural element should remain under permissible limit; 6. An operation panel installed outdoors shall be sufficiently durable and weather-resistant. All outdoor equipment shall conform to specified electrical safety standards. 2-5 Article 49 Power houses and Other Facilities Powerhouses A powerhouse shall satisfy the following: 1. A powerhouse building shall be stable with respect to self-weight, water pressure, seismic force, earth pressure, forces caused by wind, crane-weight and lifting loads of crane; 2. Structures around a turbine shall be stable with respect to vibration, and torsion induced by generator short circuit loads. 3. A powerhouse building shall not be inundated by flood, and shall not be damaged by landslide. The powerhouse shall be secure against flooding from the tailrace water level at the peak _________________________________________________________________________________________________________________________________________ Page 29 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) spillway design flood + a minimum freeboard of 2m. 4. The de-watering system shall be closed pipework system so that there are no discharge points within the powerhouse. The drainage pump shall have sufficient capacity to manage the discharge from the fracture of the largest pressurized drainage pipe in the powerhouse. 5. Powerhouse design and construction shall comply with national fire protection requirements. A minimum of two independent egress routes shall be provided from any location in the powerhouse. Article 50 Other Facilities Other hydropower civil engineering facilities such as maintenance roads or temporary facilities for construction (those other than dam, waterway, powerhouse or reservoir) shall satisfy the following: 1. Permanent facilities such as a maintenance road shall be designed to be structurally stable and, as much as possible, shall not cause serious turbid water. Access to critical locations of the project shall be available upto the 100 year flood. 2. Temporary facilities for construction works shall be stable considering time span availability during construction, and it is desired that they do not cause serious turbid water flow out of the construction areas. 2-6 Article 51 Reservoirs Prevention of Landslide Establishing a reservoir shall not cause serious water leakage to surrounding ground, seepage failure, or large-scale landslide. Potential large-scale landslide areas should be checked and if required, appropriate protection and monitoring measures be provided. Article 52 Sedimentation and Water Quality 1. Appropriate countermeasures such as dredging, flushing or establishing check dams shall be taken as necessary so that damage due to serious water rise of a river bed at upper reach areas or serious reduction of reservoir capacity does not occur because of excessive sedimentation due to the establishing of the reservoir. 2. If a deterioration of water quality in a reservoir or downstream such as cool water damage or turbid water resident is expected because of the establishing of the reservoir, appropriate countermeasures shall be taken as much as possible and shall conform to environmental study recommendations. 2-7 Down stream Article 53 Regulation of Discharge to Downstream Areas Discharge to downstream areas shall take place in accordance with the following: 1. Power Discharge: If a serious environment impact or damage to humans is expected because of the rapid water level change by the discharge from a hydropower station, appropriate _________________________________________________________________________________________________________________________________________ Page 30 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) countermeasures to mitigate possible impact or damage shall be taken. These include establishing a re-regulation pond to be able to relieve water level change and warning by sirens to downstream areas, and 2. Flood Discharge: The discharge of flood water shall be implemented so that flood damage to the downstream is not increased compared with expected flood damage before the dam was established, such that the volume of outflow from the reservoir does not increase compared with the volume of inflow to the reservoir. Appropriate countermeasures such as warning by sirens and sending notice to populations downstream shall be taken so that damage downstream is minimized. Article 54 Facilities to Discharge to Downstream Areas Facilities which may discharge a necessary amount of water for water utilization or environment prevention to the affected zone between a dam and a powerhouse shall be able to discharge small amounts of water, and shall be stable with respect to vibrations during small openings of the facilities. _________________________________________________________________________________________________________________________________________ Page 31 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Chapter 3 Electrical Facilities 3-1 Article 55 General Definitions Definitions of the terms used in Chapter 3 shall be as provided for in the following paragraphs: 1. Hydropower station “Hydropower station” means a place to generate electricity using generators with hydraulic turbines as the prime mover and other power facilities. 2. Substation “Substation” means a closed electrical operating area to transform and control electricity transmitted from the outside using transformers installed inside the compound and to further transmit the transformed electricity outside the compound. 3. User’s site “User’s site” means a place at which machines, apparatuses and devices for using electricity are installed. 4. Switching station “Switching station,” means a place other than those where power stations, substations and user’s sites are located, which is a closed electrical operating area to switch electrical circuits using switches and other machines, apparatuses and devices installed inside the compound. 5. Electrical equipment “Electrical equipment” means such electrical facilities that are installed in power stations, substations, switching stations and user’s sites comprising machines, apparatuses and devices, and electrical conductors connecting such equipment, and structures to support and hold the said equipment. 6. Hydropower electrical plant “Hydropower electrical plant” means electrical equipment comprising machines, apparatuses and devices for generating electricity, such as hydraulic turbines and generators. 7. Electrical line “Electrical line” means electrical conductors that are connected between power stations, substations, switching stations and user’s sites, and structures that support and hold such facilities. 8. Transmission line “Transmission line” means high-voltage electrical lines that are connected between power stations, substations and switching stations, and user’s sites; and medium-voltage electrical lines that are connected between hydropower stations, substations and switching stations. 9. Distribution line “Distribution line” means medium-voltage electrical lines that are connected between power stations, substations, switching stations and user’s sites; and medium and low-voltage _________________________________________________________________________________________________________________________________________ Page 32 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) electrical lines that are connected between user’s sites. 10. Electrical circuit “Electrical circuit” means a place that is charged with electricity under the normal operating conditions. 11. Low-voltage hydropower electrical plant “Low-voltage hydropower electrical plant” means systems that generate low-voltage electricity, which is used as it is as low-voltage electricity, and comprise machines, apparatuses and devices that generate low-voltage electricity, such as generators with hydraulic turbines as prime movers. 12. Single Wire Earth Return System “Single Wire Earth Return System” means a transmission system that uses the ground as an electrical circuit and distribution line. Hereinafter, it is referred to as “SWER.” 13. Supporting structure “Supporting structure” means those structures of which main purpose is to support electric conductors, such as wooden poles, iron poles, reinforced concrete poles and steel towers. 14. Primary proximity “Primary proximity” means the state in cases where an overhead electrical conductor comes close to any other structure (including cases of going side by side, and excluding cases where they cross and cases where they are installed on the same supporting structure; hereinafter the same shall apply) and there is a risk that such electrical conductor may come in contact with such other structure if an electric conductor of the electrical line is cut off and the supporting structure collapses in the case where such overhead electrical conductors are installed within the distance corresponding to the height above the ground of the supporting structure of the overhead electrical line at a horizontal distance above or to the side of the other structure (excluding cases where such overhead electrical line is installed less than 3 meters away in a horizontal distance). 15. Secondary proximity “Secondary proximity” means the state in cases where an overhead electrical conductor comes close to any other structure, and such overhead electrical conductor is installed less than 3 meters away in a horizontal distance above or to the side of such other structure. Article 56 1. Standard Frequency, Standard Voltages and Standard Test Voltages Standard Frequency Standard frequency shall be 50 Hz. 2. Standard voltages (1) Standard voltage for AC three-phase system The nominal system voltage to be applied to the electrical lines of AC three-phase system and the highest voltage for equipment corresponding to the nominal system voltage shall conform to IEC60038: Standard voltages, and the standard voltages are listed in Table 56-1. _________________________________________________________________________________________________________________________________________ Page 33 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) And the standard voltages for AC single-phase system may be applied to Table 56-1.Electrical Users may select the voltages arbitrarily, if necessary. Table 56-1 Standard voltages for AC three-phase system Nominal system voltage Highest voltage for equipment 230/400 V --220/380 V (*1) 22 kV 24 kV 35 kV 40.5 kV 115 kV 123 kV 230 kV 245 kV 500 kV 525 kV or 550 kV (*2) [Notes] *1 *2 (2) The nominal voltage of existing 220/380 V systems shall be evolved towards the recommended value of 230/400 V. (IEC) One of either voltage shall be employed for every electrical line. Standard voltages for SWER The nominal system voltage to be applied to the electrical lines of SWER and the highest voltage for equipment corresponding to the nominal system voltage are listed in Table 56-2. Table 56-2 Standard voltages for SWER Nominal system voltage Highest voltage for equipment 12.7 kV 14 kV (Line-to-earth) (Line-to-earth) 25 kV 30 kV (Line-to-earth) (Line-to-earth) 3. Standard test voltages (1) Decision on insulation strength of low-voltage electrical circuits. The insulation strength of low-voltage electrical circuits shall be decided by the insulation resistance measurement. However, if it is difficult to measure the insulation resistance, the decision may be made by leakage current measurement. (2) Decision on insulation strength of high-voltage and medium-voltage electrical circuits. The insulation strength of a high-voltage and medium-voltage electrical circuit shall be decided by an appropriate combination of the withstand voltage test, the dielectric strength test and the operation voltage test according to the kind of the electrical circuit. With respect to application of these tests and test methods according to the kind of electrical circuit, the provisions of Article 81, Article 123 and Article 147 shall be applied in addition to this item. a. Withstand voltage tests When a withstand voltage test according to the kind of electrical circuits listed in Table 56-3 is carried out in order to decide the insulation strength of the electrical circuit of a machine, apparatus and device, the circuit shall withstand these tests. The test method of the withstand voltage test shall conform to IEC60071-1: Insulation _________________________________________________________________________________________________________________________________________ Page 34 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) co-operation and other relevant IEC. However, in cases where the application of a test and test method are provided for in IEC relevant to the machines, apparatuses, and devices having such electrical circuits concerned, such provision may apply. Table 56-3 Application standard withstand voltage test for every kind of electrical circuit Kind of Electrical circuit 35 kV or lower Over 35 kV, but not higher than 245 kV Power-frequency test Short-duration Long-duration power-frequency power-frequency test test Applies --- Over 245 kV Switching impulse test Lightning impulse test --- Applies Applies (*1) --- Applies Applies (*1) Applies if necessary Applies [Notes] *1 Either the short-duration power-frequency test or the long-duration power frequency test shall be applied taking the time characteristics of insulation capability into consideration. b. Dielectric strength test In cases where the insulation strengths of electrical circuits of machines, apparatuses and devices are decided on site such as cases where such machines, apparatuses and devices are assembled on site, such electrical circuits shall withstand the dielectric strength test in which the test voltage corresponding to the kind of the electrical circuit is applied between the electrical circuit and the ground continuously for ten (10) minutes. However, in cases where the application of a test and test method are provided for in IEC relevant to the machines, apparatuses and devices having such electrical circuits concerned, that provision may apply. c. Operation voltage test In cases where the insulation strength of electrical circuits is decided on site before commencement of operation of electrical facilities, such electrical circuits shall withstand the operation voltage test in which the operation voltage under the normal operation conditions is applied. Article 57 Classification The classifications used in Chapter 3 shall be as prescribed in the following paragraph. 1. Classification of voltage AC voltages shall be classified into low-voltage, medium-voltage and high-voltage, and the range of each nominal system voltage is shown in Table 57-1. Table 57-1 Classification of voltages for AC Classification of voltage Low-voltage Medium-voltage High-voltage Range of nominal system voltage 100V or higher, but not exceeding 1 kV Over 1 kV but not exceeding 35 kV Over 35 kV _________________________________________________________________________________________________________________________________________ Page 35 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2. Classification of earthing work Earthing work shall be classified into Class A, Class B, Class C and Class D, and each resistance value to earth is listed in Table 57-2. Table 57-2 Classification of earthing work Classification of Resistance earthing work earth Class A 10 or less Class B 230 or less I* 1 Class C 10 or less Class D 100 or less to Conditions for easement of resistance value In cases where voltage to earth of a low-voltage electrical circuit exceeds 230V due to power contact between the medium-voltage electrical circuit and the low-voltage electrical circuit of the transformer, when an earth leakage breaker that cuts off the electrical circuit within 1 second is 600 installed, *1 or less. I However, if a calculated value becomes less than 5, it shall not be necessary to obtain resistance less than 5, and if a calculated value becomes more than 10, it shall not be necessary to obtain resistance more than 10. In the case where earthing arises in a low-voltage electrical circuit, when an earth leakage breaker that acts within 0.5 seconds is installed, the resistance value shall be 500 or less. In the case where earthing arises in a low-voltage electrical circuit, when an earth leakage breaker that acts within 0.5 seconds is installed, the resistance value shall be 500 or less. [Notes] *1 Single-line earth fault current (I) of an electrical circuit in the medium-voltage side in Class B earthing may conform to an actual value or either of the following values. (1) Medium-voltage electrical circuit of isolated neutral system (excluding those that are provided for in the next item) a. Electrical circuits using an electric conductor other than a cable I1 V1 L 100 1 3 150 (As for the value of the second term on the right side, any fraction less than its decimal point shall be rounded up. If I1 becomes less than 2, it shall be 2.) b. Electrical circuits using a cable for an electrical conductor V1 L'1 3 I1 1 2 (As for the value of the second term on the right side, any fraction less than its decimal point shall be rounded up. If I1 becomes less than 2, it shall be 2.) _________________________________________________________________________________________________________________________________________ Page 36 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) c. Electrical circuits using an electrical conductor other than a cable and electrical circuits using a cable for the electrical conductor V1 V1 L 100 L 1 I1 1 3 3 150 2 (As for values of the second and third terms on the right side, if the respective values become negative, they shall be 0. As for the value of I1, its fraction less than its decimal point shall be rounded up. If I1 becomes less than 2, it shall be 2.) (2) I1: V: Single-line earth fault current (A shall be used as the unit.) Voltage obtained from dividing the nominal system voltage of the electrical circuit by 1.1 (kV shall be used as the unit.) L: Extension of the electrical line of the medium-voltage electrical circuit (excluding that using a cable for an electrical conductor) to be connected to the same bus bar (km shall be used as the unit.) L': Extension of the electrical line of the medium-voltage electrical circuit (limited to that using a cable for an electrical conductor) to be connected to the same bus bar (km shall be used as the unit.) Medium-voltage electrical circuits of solidly earthed neutral systems and medium-voltage electrical circuits of isolated neutral systems that directly connect with electric boilers, electric furnaces, etc. to be used without insulation against the ground (excluding those which are provided for in the next item) I2 I 12 V2 2 3R 2 10 6 (Any fraction less than the decimal point shall be rounded up.) (3) I2: Single-line earth fault current (A shall be used as the unit.) I1: Single-line earth fault current calculated in the preceding item V: Nominal system voltage of the electrical circuit (kV shall be used as the unit.) R: Electric resistance value of the resistance used in the neutral point (including the resistance to earth value of the neutral point. shall be used as the unit.) Medium-voltage electrical circuits of earthed neutral point reactor systems 2 V2 V2 X R 3 3 3 3 10 I 1 2 10 I3 2 R X2 R X2 2 (Any fraction less than the decimal point shall be rounded up. If I3 becomes less than 2, it shall be 2.) I3: Single-line earth fault current (A shall be used as the unit.) _________________________________________________________________________________________________________________________________________ Page 37 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. I1: Single-line earth fault current calculated in Item 1. V: R: Nominal system voltage of the electrical circuit (kV shall be used as the unit.) Electric resistant value of the reactor used on the neutral point (including the resistance to earth value for the neutral point) X: Inductive reactance value of the reactor used on the neutral point ( shall be used as the unit.) Classification of Structure for Transmission and Distribution Lines The electric transmission towers can be broadly classified as;Lattice Structure A lattice tower is a framework construction made of galvanized steel sections. Lattice towers are used for power lines of all voltages and are the most common type for high-voltage transmission lines. Tubular Pole Structure Steeped Poles- Stepped poles shall be made from one length of tube, seamless or welded, the diameter being reduced in parallel steps by passing the tubes through series of dies. Where welded tubes are used they shall have one longitudinal weld seam only. Swaged Poles- Swaged poles shall be made of seamless or welded tubes of suitable lengths swaged and joined together. No circumferential joints shall be permitted in the individual tube lengths of the poles. If welded tubes are used they shall one longitudinal weld seam only; and the longitudinal welds shall be staggered at each swaged joint. RCC Poles-Reinforced Concrete Poles In practice reinforced concrete poles are used for distribution purposes at low voltages. However, for long distance transmission at higher voltage, steel towers are invariably employed. Steel towers have greater mechanical strength, longer life, can withstand most severe climatic conditions and permit the use of longer spans. 3-2 Article 58 Fundamental Requirements Prevention of Electric Shock and Fire Caused by Electrical Facilities The electrical facilities shall be installed in such a manner so as not to cause electric shock, fire and other accidents that may endanger the human body and damage objects. Article 59 Insulation of Electrical Circuits against Grounds Electrical circuits shall be insulated from the ground. However, the same shall not apply to such cases where it is structurally inexecutable and it is presumed not likely to be dangerous taking into consideration the forms of use which are normally foreseeable, or where a circuit is secured by earthing to prevent danger in case of emergency, such as over voltage _________________________________________________________________________________________________________________________________________ Page 38 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) invasion due to power contact, or other necessary measures for safety and security have been taken. Article 60 Provision of Earthing on Necessary Points in Electrical Facilities On necessary points in electrical facilities, earthing shall be provided so as to prevent electric shock, fire and other accidents that may harm the human body and damage objects caused by abnormal increases in electric potential, over voltage invasion, etc. However, for the portions pertaining to electrical circuits, earthing shall be provided for as prescribed in the provisions of Article 59. Article 61 Protection against Over current and Earth Faults 1. On necessary points in electrical circuits, an over current overcurrent relay and circuit breaker to trip circuit breaker shall be installed so as to protect electrical conductors, machines, apparatuses and devices from overheating burnout due to over current, and to prevent occurrence of fire. 2. Appropriate measures, such as the provision of an earth fault relay , shall be taken to the electrical circuits so as not to damage electrical conductors and machines, apparatuses and devices and not to cause electric shock and fire even if an earth fault occurs. However, the same shall not apply to such a case where there is no risk of earth fault because the machines, apparatuses and devices are installed in a dry place. Article 62 Isolation from High-voltage and Medium-voltage Electrical Facilities Electrical facilities to be installed on high-voltage and medium-voltage electrical circuits shall be installed in such a manner so as not to allow anybody to contact them easily. However, the same shall not apply to such a case where there is no risk of danger due to contacting the facilities. Article 63 Prevention of Danger Due to Breakage of Electrical Conductors Conductors, guys, overhead ground wires and other wires to be used for electrical facilities shall be installed in such a manner so as to cause no wire breaking under normal operating conditions. Article 64 Prevention of Damage to Other Facilities Electrical facilities, if they are close to or cross over other facilities and plants, shall be installed in such a manner so as not to damage other facilities and plants. Article 65 Prevention of Danger Due to Collapse of Supporting Structures Supporting structures of overhead electrical lines shall be installed in such a manner so that they will not fall down due to changes in weather conditions, impacts and other external environmental influences, which are normally foreseeable. Article 66 Prevention of Electrical and Magnetic Interference Electrical facilities shall be installed in such a manner so as not to cause electrical and magnetic interference to the human body and/or to the functions of other facilities. Article 67 Prevention of Serious Obstacles to Power Generation and Power Supply, and Prevention of Damage to Other Electrical Facilities Caused by Damage and Destruction of Electrical Facilities _________________________________________________________________________________________________________________________________________ Page 39 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 1. Electrical facilities shall be installed in such a manner so as not to cause any serious obstacle to power generation and power supply that may be caused by damage and/or destruction of such electrical facilities. 2. Electrical facilities shall be installed in such a manner so as not to cause any damage to any other electrical facilities that may be caused by damage and/or destruction of such electrical facilities. Article 68 Prevention of Pollution Electrical facilities shall be installed in such a manner so as to cause no pollutions, air, water, noise, vibration, discharge of insulating oil, and otherwise which may endanger the human body and damage other objects. 3-2 Common Rules for Electrical Facilities 3-3-1 Protective Safety Installations Article 69 1. Prevention of Entry of Any Person Other than Operators to Closed Electrical Operating Areas Where High-voltage and Medium-voltage Electrical Facilities Are Installed Scope of application For any place where high-voltage and medium-voltage electrical facilities are installed, signs warning that the electrical facilities are dangerous to any person other than operators shall be provided and appropriate measures shall be taken so that no person other than operators can easily enter into the closed electrical operating area. However, the same shall not apply to any place where there is no danger of entry of any person due to conditions of the land. This Article shall apply to the following places: (1) Hydropower stations, substations and switching stations (hereinafter referred to as the "Stations") where high-voltage and medium-voltage electrical facilities are installed, (2) User’s sites where high-voltage and medium-voltage electrical facilities are installed (hereinafter referred to as the "HV and MV user’s sites"), and (3) Places where electrical facilities to which any high-voltage and medium-voltage overhead and underground electrical line is connected are installed. 2. Installations for preventing entry Appropriate measures listed below shall be taken so as to prevent any person other than operators from entering into the Stations: (1) (2) (3) Provision of installing external fences or wall, or strong walls and roofs Provision of signs to prohibit entry at the entrances/exits Provision of a locking device or another appropriate device at the entrances/exits _________________________________________________________________________________________________________________________________________ Page 40 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. Particularities of external fences or wall The height of external fences or wall shall not be lower than 1,800 mm. Where the external fence or wall and live parts are located closely each other, the sum of the height of the external fence or wall and vertical clearance from the external fence or wall to the live part shall not be smaller than the value provided for each kind of the nominal system voltage indicated in Table 69-1. In addition, the boundary clearance from the external fence or wall to the live part shall not be smaller than the value provided for each kind of structure of the external fence or wall indicated in Table 69-1. “N” represents the minimum insulating clearance of line-to-earth here, and it shall conform to the provisions in Article 82. Table 69-1 Clearance from external fence or wall to live parts Kind of nominal system voltage 35 kV or less Over 35 kV, but not higher than 160 kV Over 160 kV Article 70 1. Sum of the height of external fence or wall and the vertical clearance from the external fence or wall to the live part [mm] 5,000 6,000 Value obtained by adding 60 mm for every 10 kV and its fraction exceeding 160 kV to 6 m Boundary clearance [mm] Wall: N+1,000 Fence: N+1,500 Protection of Operators against Dangers of High-voltage and Medium-Voltage Electrical Facilities in a Closed Electrical Operating Area Scope of application This Article shall apply to the following places: (1) (2) (2) 2. The Stations; The HV and MV user’s sites; and Places where electrical facilities to which any high-voltage and mediumvoltage overhead and underground electrical line is connected are installed. Securing maintenance space At such places where high-voltage and medium-voltage electrical facilities are needed, patrol aisles and other maintenance spaces shall be provided so as to enable operators to operate and carry out maintenance safely. 3. Prevention of contact with live parts For live parts of high-voltage and medium-voltage electrical facilities, appropriate measures listed below shall be taken so as to prevent operators from contacting such facilities easily. (1) Installation for prevention of contacting Where the height of live parts of electrical equipment is N+2,250 mm or less (the minimum height shall be 2,500 mm), appropriate measures listed below shall be taken. “N” represents the minimum insulating clearance of line-to-earth here, and it shall conform to _________________________________________________________________________________________________________________________________________ Page 41 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) the provisions of Article 82. (2) a. Provision of installing protective fences or wall b. Provision of signs to prohibit entry at the entrances/exits c. Provision of a locking device or another appropriate device at the entrances/exits Particularities of protective fences or wall The height of external fences or wall shall be 1,800 mm or higher. The protective barrier clearance from the protective fence or wall to live parts shall be, at least, the value provided for every kind of structure of the protective fence or wall indicated in Table 70-1. In this connection, “N” means the minimum insulating clearance of line-to-earth, and it shall conform to the provision in Article 82. Table 70-1 Distance/clearance from protective fence or wall to live parts Structure of protective fence or wall Protective barrier clearance [mm] Wall without opening N Fence (The highest voltages for equipment N+100 is over 52 kV) Fence (The highest voltages for equipment N+80 is 52 kV or lower) 4. Prevention of misoperation For high-voltage and medium-voltage electrical facilities, appropriate measures listed below shall be taken so as not to allow operators to carry out faulty maintenance and operation. (1) Provision of clear phase-signs and equipment-number-signs At such places where considered necessary, clear phase-signs and equipment-number-signs are to be furnished. (2) Provision of installing indicators showing switching status Switching devices, such as circuit breakers, power fuses, load switches and disconnecting switches shall have an indicator that indicates switching status of the device. However, the same shall not apply to devices for which the switching status can be confirmed easily. (3) Provision of interlock Disconnecting switches shall be provided with an interlock so that the disconnecting switch cannot be opened when loaded with load current. 5. Installation of transformers that transform high-voltage directly into low-voltage No transformer that transforms high-voltage directly into low-voltage shall be installed. Article 71 Prevention of Danger of Low-voltage Hydropower Electrical Plants _________________________________________________________________________________________________________________________________________ Page 42 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) For live parts of low-voltage hydropower electrical plants and connecting electrical conductors, appropriate measures shall be taken so as to prevent any person other than operators from contacting them easily. Article 72 Prevention of Climbing onto Supporting Structures No metal step for operators’ use to climb onto supporting structures for overhead transmission lines shall be provided at the height below 1.8 m from the ground surface. However, the same shall not apply to such cases as mentioned below: (1) Where any supporting structures inside of which metal steps can be stored are installed. (2) Where the supporting structures are equipped with any device to prevent climbing. (3) Where any fence, wall, etc. is installed surrounding the supporting structures so as to prevent any person other than operators from entering. (4) Where the supporting structures are installed in the mountainside into which no person can enter easily. Article 73 1. Prevention of Damage by Small Animals to Electrical Facilities Prevention of contact with live parts Appropriate measures shall be taken so as not to allow small animals to contact live parts of high-voltage and medium-voltage electrical facilities easily. 2. Prevention of intrusion into the inside of electrical facilities Appropriate measures shall be taken so as not to allow small animals to intrude into the inside of high-voltage and medium-voltage electrical facilities. Article 74 1. Prevention of Damage by Rainwater to Electrical Facilities Prevention of damage by flood The Stations shall be installed in such a manner so as not to suffer damage from submersion due to flood, which is normally foreseeable. 2. Prevention of damage by rainwater Appropriate measures listed below shall be taken so as not to suffer damage to the high-voltage and medium-voltage electrical facilities from rainwater under the normal conditions. (1) Installation of drainage facilities Appropriate measures shall be taken so as to drain off the rainwater, the rainfall of which is normally foreseeable. In the areas where the drainage facilities are installed, the openings of drainage ditches and drainage channels shall be properly covered so as to avoid danger of operators and any other persons’ falling into such ditches and channels. (2) Waterproofing of buildings in which electrical equipment is installed Buildings in which high-voltage and medium-voltage electrical equipment is installed shall be constructed in such a manner so as to have no leakage of water into the buildings. _________________________________________________________________________________________________________________________________________ Page 43 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 75 1. Prevention of Fire Caused by Electrical Equipment Clearance between electrical equipment that generates an arc and inflammables Electrical equipment that generates an arc during operation, such as high-voltage and medium-voltage switching devices, circuit breakers and surge arresters, to be installed in Stations and HV and MV user’s sites shall be installed with at least the clearance prescribed in Table 75-1 from wooden walls, ceilings and other inflammables so that there is no risk of fire. However, the same shall not apply to cases where they are separated with a fireproof object. Table 75-1 Clearance between electrical equipment that generates an arc and inflammables Clearance between electrical equipment that Classification of voltage generates an arc and inflammables Medium-voltage 1m High-voltage 2m 2. Clearance between transformers, etc. and buildings Appropriate measures listed below shall be taken so as to avoid risks of fire spreading to other transformers and buildings should a fire start in an oil-insulated transformer and reactor (hereinafter in this article the "Transformers") to be connected to electrical circuits of effectively earthed systems installed in Stations and HV and MV user’s sites. (1) Clearance High-voltage and medium-voltage transformers shall be installed so that the clearance between the transformer and other transformers or buildings is at least the value shown in Table 75-2. However, the same shall not apply where they are separated with a firewall. Table 75-2 Clearance between high-voltage and medium-voltage transformers and other transformers or buildings Amount of With other With fireproof With non-fireproof insulating oil transformers [m] buildings [m] buildings [m] Over 1,000 L, but not 3 3 7.6 exceeding 2,000 L Over 2,000 L, but not 5 5 10 exceeding 20,000 L Over 20,000 L, but not 10 10 20 exceeding 45,000 L Over 45,000 L 15.2 15.2 30.5 (2) Particularities of firewalls When a firewall is installed, it shall conform to the following: a. b. c. 3. The firewall shall be self-supporting with poles and a wall and shall withstand a fire for one hour. Height: top of the expansion chamber, otherwise the top of the transformer tank. Length: width or length of the. Installation of extinguishers Appropriate extinguishers shall be installed in Stations and HV and MV user’s sites. _________________________________________________________________________________________________________________________________________ Page 44 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3-3-2 Prevention of Electrical and Magnetic Interference Article 76 1. Prevention of Electrical Inductive Interference and Electrical Wave Interference Prevention of electrostatic inductive interference with overhead telecommunication lines Overhead electrical lines shall be installed in such a manner so as not to cause interference with communication through overhead telecommunication lines due to electrostatic inductive action. However, the same shall not apply to the case where consent of the controller of the overhead telecommunication line is obtained. 2. Prevention of electrostatic inductive interference with persons In addition to installing the overhead electrical lines in such a manner that the electrical field strength at 1 m above the ground surface does not exceed 3 kV/m, the same shall be installed so that there is no risk of danger to persons due to electrostatic inductive action. The above shall not apply to cases where the overhead electrical line is installed in a place where the traffic volume is not significant such as rice fields, cultivated fields and mountains in a way so that there is no risk of danger to persons. 3. Prevention of electromagnetic interference with overhead telecommunication lines Overhead electrical lines shall be installed in such a manner so as not to cause interference with communication through overhead telecommunication lines due to electromagnetic inductive action. However, the same shall not apply to the case where consent of the controller of the overhead telecommunication line is obtained. 4. Prevention of electromagnetic interference with persons Overhead electrical lines shall be installed in such a manner so as to avoid risks of danger to persons due to electromagnetic inductive action. 5. Prevention of electrical wave interference Overhead electrical lines shall be installed in such a manner so as not to cause continuous and serious interference with functions of radio equipment such as radio, TV broadcasting and microwave communication. 3-3-3 Prevention of Pollution Article 77 1. Prevention of Pollution by Insulating Oil Prevention of outflow and seepage of insulating oil Appropriate measures shall be taken so as to prevent outflow of insulating oil to the outside of the compound and seepage into the ground for Stations and HV and MV user’s sites where high-voltage and medium-voltage oil-insulated transformers to be connected to electrical circuits of effectively earthed systems and oil tanks are installed. _________________________________________________________________________________________________________________________________________ Page 45 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2. Prohibition of installation of equipment containing polychlorinated biphenyl Electrical equipment, for which insulating oil containing polychlorinated biphenyl is used, must not be installed. Article 78 Prevention of Emissions of SF6 Gas For electrical equipment that uses SF6 gas, appropriate measures shall be taken so that SF6 gas is not emitted into the atmosphere. 3-4 Hydropower Electrical Plants, Substations and Switching Stations 3-4-1 Electrical Equipment 3-4-1-1 Article 79 1. Insulation Insulation Co-ordination Insulation of electrical circuits Electrical circuits in hydropower stations, substations and switching stations (hereinafter the "Stations"), and user’s sites where high-voltage and medium-voltage electrical facilities are installed (hereinafter the "HV and MV user’s sites") shall be insulated from the ground excluding the following portions: (1) Connection points between earthing conductors to be installed in accordance with the provisions of Article 95-1-(3), Article 95-2 and Article 95-4 and electrical circuits. (2) For part of the following items where it is unavoidable insulation not be provided: a. b. 2. SWER to be installed in accordance with the provision of Article 95-3. Electrical equipment for which it is necessary to use a part of electrical circuits without insulating from the ground. Insulation co-ordination The concept of insulation co-ordination for Stations and HV and MV user’s sites shall conform to IEC60071-1 and other relevant IEC. The insulation strength of electrical equipment shall be chosen taking into consideration the service environment and the characteristics of protective devices that can be used with relation to various kinds of overvoltage that are generated in the system in which the electrical equipment is used, and electrical circuits of the electrical equipment shall be installed to have the insulation strength listed below. (1) Insulation strength of electrical circuits The insulation strength of electrical circuits shall be such that there is no risk of danger due to breakdown with consideration given to the highest voltage for equipment to be impressed to the circuit during its lifetime, a temporary over voltage under abnormal conditions, switching over voltage conceivable when the switching device is operated and lightning over voltage. (2) Insulation strength of windings in transformers _________________________________________________________________________________________________________________________________________ Page 46 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The insulation strength of windings in transformers shall be such that there is no risk of danger due to breakdown with consideration given to the highest voltage for equipment to be impressed to the circuit during its lifetime, a temporary over voltage under abnormal conditions, switching over voltage conceivable when the switching device is operated and lightning over voltage. Article 80 1. Protection against Lightning and Switching Overvoltage Protection of electrical equipment from direct stroke of lighting Stations and HV and MV user’s sites shall be appropriately equipped with lightning guards, such as overhead ground wires and lightning rods, in order to protect the electrical circuits in Stations and HV and MV user’s sites from direct stroke of lighting. However, the same shall not apply to low-voltage hydropower electrical plants. 2. Installation of surge arresters Surge arresters to be installed in electrical circuits in the Stations and HV and MV user’s sites shall be installed as shown below. Surge arresters, here, mean devices that protect insulation of electrical equipment by restricting over voltage through discharge when the crest value of over voltage caused by lightning and switching of the circuit exceeds a certain value, and have an ability to restore the normal conditions without disturbing the normal status of the power system. Devices with low self-restoring ability, such as devices with air-gaps, are not suitable as surge arresters. (1) Installation points for surge arresters Surge arresters shall be installed at points listed below in high-voltage and medium-voltage electrical circuits or at locations close to such points so as not to damage electrical equipment to be installed in electrical circuits in the Stations and HV and MV user’s sites by over voltage. However, the same shall not apply to cases where there is no risk of damage to such electrical equipment. a. Receiving and outgoing points on overhead electrical lines in the Stations (2) b. Receiving points on the HV and MV user’s sites to which power is supplied from high-voltage and medium voltage overhead electrical lines c. Locations where there is a risk that protective effects of surge arresters installed in accordance with the above provisions may not be achieved. Performances of surge arresters The performances of surge arresters to be installed in the Stations and HV and MV user’s sites shall conform to the following provisions, IEC60099 and other relevant IEC. a. Rated voltage The rated voltage of surge arresters shall be chosen based on the principle that the surge arrester can perform the prescribed operating duties under the condition of temporary overvoltage to occur in the Stations and HV and MV user’s sites due to a single-line earth fault and load rejection. b. Nominal discharge current _________________________________________________________________________________________________________________________________________ Page 47 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) For the nominal discharge current of surge arresters, a value not smaller than the nominal discharge current listed in Table 80-1 shall be chosen. Table 80-1 Nominal discharge current of surge arresters Nominal discharge Installation point of the surge arrester current Surge arresters to be installed in high-voltage electrical circuits 10 kA Surge arresters to be installed It is unnecessary to treat switching 5 kA in medium-voltage electrical surge. circuits 10 kA Surge arresters to be installed in medium voltage electrical circuits to be connected with an overhead distribution line to be installed on the 10 kA top of an overhead transmission electrical line Article 81 1. Insulation Strength of Electrical Circuits in Electrical Equipment Scope of application According to Article 56-3-(2), insulation of electrical circuits in Stations and HV and MV user’s sites shall withstand the following tests. 2. Electrical circuits in generators (1) Withstand voltage test According to Article 56-3-(2)-a, electrical circuits in generators shall withstand the withstand voltage test based on Article 56-3-(2)-a and the relevant IEC. However, the insulation strength of electrical circuits in generators of low-voltage hydropower electrical plants may be confirmed by the insulation resistance measurement. (2) Dielectric strength test According to Article 56-3-(2)-b, after installation on site, electrical circuits in generators shall withstand the dielectric strength test in which the test voltage provided for each class of electrical circuit listed in Table 81-1 is applied between the electrical circuit and the ground for ten (10) minutes continuously. However, the same shall not apply to cases that fall under any one of the following items. a. In cases where the electrical circuit in the generator withstands the dielectric strength test in which DC voltage 1.7 times of the test voltage corresponding to the class of the electrical circuit listed in Table 81-1 between the electrical circuit and the ground for ten (10) minutes continuously. b. In cases where it is confirmed by the insulation resistance measurement that the electrical circuit in the generator of a low-voltage hydropower electrical plant has the required insulation strength. c. In cases where the insulation strength confirmed by the withstand voltage test is maintained after installation on site. Table 81-1 Dielectric strength test for electrical circuits in generators Class of the electrical circuit Generators with the highest voltage equipment not higher than 7 kV Test voltage for The voltage 1.5 times of the highest voltage for equipment (500 V when it is lower than 500 V) is _________________________________________________________________________________________________________________________________________ Page 48 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Generators of which the highest voltage for equipment exceeds 7 kV (3) impressed The voltage 1.25 times of the highest voltage for equipment (10.5 kV when it is lower than 10.5 kV) is impressed Operation voltage test According to Article 56-3-(2)-c, at the first excitation, the electrical circuits in generators shall withstand the operation voltage test in which the operation voltage is applied between the electrical circuit and the ground. 3. Electrical circuits in transformers This paragraph shall not apply to transformers for testing purposes, instrument transformers and those used for special uses. (1) Withstand voltage test According to Article 56-3-(2)-a, electrical circuits in transformers shall withstand the withstand voltage test based on Article 56-3-(2)-a and the relevant IEC. (2) Dielectric strength test According to Article 56-3-(2)-b, after installation on site, electrical circuits in transformers shall withstand the dielectric strength test in which the test voltage provided for each class of electrical circuit listed in Table 81-2 is applied for ten (10) minutes continuously. However, the same shall not apply to cases where it is judged that the insulation strength confirmed by the withstand voltage test is maintained after installation on site. Table 81-2 Classification A B C D Dielectric strength test for electrical circuits in transformers Class of electrical circuit Windings with the highest voltage for equipment not higher than 7 kV Winding with the highest voltage for equipment over 7 kV but not higher than 35 kV Windings with the highest voltage for equipment over 35 kV to be connected to the electrical circuit of the isolated neutral system (including windings that are earthed using a potential transformer) Windings with the highest voltage for equipment over 35 kV (limited to star connections) to be connected to the electrical circuit of the solidly earthed neutral system (excluding windings that are earthed using a potential transformer and those listed under the class E), and, in the case of winding of a star connection, equipped with a surge arrester at the neutral point. Test voltage The voltage 1.5 times of the highest voltage for equipment (500 V when it is lower than 500 V) is impressed between the winding being tested and other windings, the core and the case. The voltage 1.25 times of the highest voltage for equipment (10.5 kV when it is lower than 10.5 kV) is impressed between the winding being tested and other windings, the core and the case. The voltage 1.25 times of the highest voltage for equipment is impressed between the winding being tested and other windings, the core and the case. (1) After earthing a randomly chosen terminal other than the neutral terminal of the winding to be tested, a randomly chosen terminal of another winding (if there are two (2) or more other windings, each of the windings), the core and the case, three-phase alternating current of the voltage 1.1 times of the highest voltage for equipment (75 kV when it is lower than 75 kV) is impressed to each terminal other than the neutral terminal of the winding to be tested. (2) If it is difficult to test with three-phase alternating current, a. Single-phase alternating current of the voltage 1.1 times of the highest voltage for equipment (75 kV _________________________________________________________________________________________________________________________________________ Page 49 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) when it is lower than 75 kV) is impressed between the ground and the neutral terminal of the winding being tested and a randomly chosen terminal other than the terminal that is earthed. E F Windings with the highest voltage for equipment not lower than 100 kV (limited to those of star connections) to be connected to the electrical circuit of the solidly earthed neutral system and equipped with a surge arrester at the neutral point. Windings with the highest voltage for equipment over 100 kV (limited to those of star connections) to be connected to the electrical circuit of the solidly earthed neutral system, where the neutral point is directly earthed. Other windings G (3) Further, the single-phase alternating current of the voltage 0.64 times of the highest voltage for equipment is impressed between the ground and the neutral terminal of the winding. After earthing the neutral terminal of the winding being tested, a randomly chosen terminal of another winding (if there are two (2) or more other windings, each of the windings), the core and the case, the voltage 0.72 times of the highest voltage for equipment is impressed between a randomly chosen terminal other than the neutral terminal of the winding being tested and the ground. Further, the voltage 0.3 times of the highest voltage for equipment is impressed between the ground and neutral terminal. After earthing the neutral terminal of the winding being tested, a randomly chosen terminal of another winding (when there are two (2) or more other windings, each of the windings), the core and the case, the voltage 0.64 times of the highest voltage for equipment is impressed between a randomly chosen terminal other than the neutral terminal of the winding being tested and the ground. The voltage 1.1 times of the highest voltage for equipment (75 kV when it is below 75 kV) is impressed between the winding being tested and other windings, the core and the case. Operation voltage test According to Article 56-3-(2)-c, before commencement of operation, the electrical circuits in transformers shall withstand the operation voltage test in which the operation voltage is applied between the electrical circuit and the ground for ten (10) minutes continuously. 4. Electrical circuits in machines apparatuses and devices This Paragraph shall apply to electrical circuits in switching devices, circuit breakers, reactors, power capacitors, instrument transformers, surge arresters, other machines, apparatuses and devices, connection conductors and bus bars (hereinafter referred to as the "Machines"), excluding electrical circuits in generators in Article 81-2 and electrical circuits in transformers in Article 81-3. (1) Withstand voltage test According to Article 56-3-(2)-a, electrical circuits in the Machines shall withstand the withstand voltage test based on the relevant IEC. (2) Dielectric strength test According to Article 56-3-(2)-b, after installation of the Machines on site, electrical circuits in the Machines shall withstand the dielectric strength test in which the test voltage provided for each class of electrical circuit listed in Table 81-3 is applied between the electrical circuit and the ground for ten (10) minutes continuously. However, the same shall not apply to cases that fall under any one of the following items. a. In cases where the electrical circuit in the connection conductor for the Machines and the bus _________________________________________________________________________________________________________________________________________ Page 50 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) bar, in which cables are used as electrical conductors, withstand the dielectric strength test in which the DC voltage two (2) times of the test voltage corresponding to the class of the electrical circuit listed in Table 81-3 is applied between the electrical circuit and the ground for ten (10) minutes continuously. b. In cases where electrical circuits in earthing potential transformers, coupling capacitors for power line carriers, coupling reactors for power line carriers and surge arresters, of which electrical equipment conform to the relevant IEC, are installed. c. In cases where electrical circuits in the Machines for the neutral point of resistances, reactors, etc. to be connected to earthing conductors as a part of an earthing arrangement, of which electrical equipment conform to the relevant IEC, are installed. d. In cases where the insulation strength confirmed by the withstand voltage test is maintained after installation on site. Classification A B C D E F (3) Table 81-3 Dielectric strength test for electrical circuits in Machines Class of electrical circuit Test voltage Machines with the highest voltage for The voltage 1.5 times of the highest voltage equipment not higher than 7 kV for equipment (500 V when it is lower than 500V) is impressed Machines with the highest voltage for The voltage 1.25 times of the highest voltage equipment over 7 kV but not higher for equipment (10.5 kV when it is lower than than 35 kV 10.5 kV) is impressed Machines with the highest voltage for The voltage 1.25 times of the highest voltage equipment over 35 kV to be for equipment is impressed connected to the electrical circuit of the isolated neutral system (including Machines that are earthed using a potential transformer) Machines with the highest voltage for The voltage 1.1 times of the highest voltage equipment over 35 kV to be for equipment (75 kV when it is lower than 75 connected to the electrical circuit of kV) is impressed the solidly earthed neutral system (excluding Machines that are earthed using a potential transformer) (excluding those listed under Classes E and F) Machines with the highest voltage for The voltage 0.72 times of the highest voltage equipment over 100 kV to be for equipment is impressed. connected to the electrical circuit of the solidly earthed neutral system (excluding those listed under Class F) Machines with the highest voltage for The voltage 0.64 times of the highest voltage equipment over 100 kV to be for equipment is impressed. connected to the electrical circuit in the Stations and HV and MV user’s sites where the neutral point is directly earthed Operation voltage test According to Article 56-3-(2)-c, before commencement of operation, electrical circuits in the Machines shall withstand the operation voltage test in which the operation voltage is applied between the electrical circuit and the ground for ten (10) minutes continuously. _________________________________________________________________________________________________________________________________________ Page 51 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 82 1. Insulating Clearance of Bus Bars Insulation strength of bus bars Bus bars shall be chosen from those of which insulation strength is stronger than that of the insulation strength of electrical equipment to be installed in the Stations and HV and MV user’s sites under any operating conditions taking into consideration abnormal voltage likely to have at an accident. 2. Insulating clearance of bus bars This Paragraph shall apply to the line-to-earth and line-to-line insulating clearance for outdoor and indoor bare electrical conductors in the Stations and HV and MV user’s sites. (1) Minimum insulating clearance The minimum insulating clearance shall be not smaller than the minimum line-to-earth and line-to-line insulating clearance listed in Table 82-1. Table 82-1 Minimum insulating clearance Highest voltage for equipment Minimum line-to-earth insulating Minimum line-to-line insulating [kV] clearance [mm] clearance [mm] 24 220 280 40.5 350 450 123 1100 1400 245 1900 2450 525 4100 5800 550 (2) Standard clearance for bus bars As a general rule, the standard values for insulating clearance for bus bars shall be the standard values for line-to-earth and line-to-line insulating clearance listed in Table 82-2. Highest voltage for equipment [kV] 24 40.5 123 245 525 550 Table 82-2 Standard clearance for bus bars Outdoor Indoor Standard value for Standard value for Standard value for Standard value line-to-earth line-to-line line-to-earth for line-to-line insulating insulating insulating insulating clearance clearance [mm] clearance clearance [mm] [mm] [mm] 400 700 300 450 500 900 420 580 1400 2300 ----2300 3600 ----8000 3-4-1-2 Article 83 1. 8000 --- --- Thermal Strength and Mechanical Strength Thermal Strength of Electrical Equipment Thermal strength of electrical equipment Electrical equipment to be installed in the Stations and HV and MV user’s sites shall withstand _________________________________________________________________________________________________________________________________________ Page 52 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) the heat generated by electrical equipment in normal operations. 2. Confirmation of thermal strength of electrical equipment It shall be confirmed that the temperature rise of the electrical equipment does not exceed the allowable maximum temperature of the electrical equipment or the maximum temperature under which there is no risk of damage to the electrical equipment, when the temperature rise test based on the following items and the standard concerning the electrical equipment is carried out. (1) Generators The temperature rise of generators when operated with the rated load shall not exceed the allowable maximum temperature corresponding to its thermal strength class, and the thermal strength of generators shall be such that there is no risk of damage within the range of the allowable maximum temperature. Temperature rise of generator winding insulation and other components shall be as per IEC 60034-1 table 7. (2) Bearings of hydraulic turbines and generators The thermal strength of bearings of hydraulic turbines and generators shall be such that there is no risk of damage due to the maximum temperature to be generated in the bearing with the rated load. (3) Transformers This Item shall not apply to testing transformers, instrument transformers and transformers for special use. The temperature rise of transformers when operated with the rated load shall not exceed the allowable maximum temperature corresponding to its thermal strength class, and the thermal strength of transformers shall be such that there is no risk of damage within the range of the allowable maximum temperature. Temperature rise of transformer shall be as per IEC 60076-2 clause 4. (4) MV and HV Switchgear This Item shall apply to electrical circuits in switching devices, circuit breakers, reactors, power capacitors, instrument transformers, surge arresters, other Machines, bus bars, and connection conductors for Machines, excluding generators in Item 2-(1), bearings of hydraulic turbines in Item 2-(2) and transformers in Item 2-(3). The temperature rise of switchgear when operated with the rated load shall not exceed the allowable maximum temperature corresponding to its thermal strength class, and the thermal strength of Machines shall be such that there is no risk of damage within the range of the allowable maximum temperature. Temperature rise shall be as limited to the values given in IEC 62271-1 table 3. Article 84 Mechanical Strength of Electrical Equipment against Short-circuit Current 1. Mechanical strength of electrical equipment against short-circuit current Generators, transformers, reactive power compensator, switching devices, bus bars and insulators for supporting bus bars to be installed in the Stations and HV and MV user’s sites shall withstand the mechanical shock caused by short-circuit current. 2. Confirmation of mechanical strength of electrical equipment against short-circuit current _________________________________________________________________________________________________________________________________________ Page 53 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The mechanical strength of generators, transformers, reactive power compensator, switching devices, bus bars and insulators supporting bus bars in Stations and HV and MV user’s sites shall be designed and installed based on the standards concerning the electrical equipment taking into consideration the electromagnetic force due to short-circuit current ( IEC 60034-1, 60076 and IEC 60865-1 and 2) Article 85 Mechanical Strength of Hydraulic Turbines and Generators 1. Mechanical strength of hydraulic turbines and generators Hydraulic turbines and generators to be installed in hydropower stations shall withstand the mechanical shock with the maximum speed in the rotating parts of the hydraulic turbine and the generator connected to the hydraulic turbine and with the maximum water pressure in the parts of the hydraulic turbine receiving the water pressure. 2. Confirmation of the mechanical strength of hydraulic turbines and generators The mechanical strength of hydraulic turbines and generators shall be designed, installed and tested based on the following items and the standards concerning hydraulic turbines and generators. (1) Design and installation of mechanical strength (2) a. The mechanical strength of rotating parts of hydraulic turbines and generators connected to the hydraulic turbines shall be designed and installed so that there is no risk of damage at the maximum runaway speed. c. The mechanical strength of parts of hydraulic turbines receiving water pressure shall be designed and installed according to the standards concerning hydraulic turbines and generators. Test of mechanical strength a. Rotating parts of hydraulic turbines and generators connected to the hydraulic turbines shall be such that there is no risk of damage at the maximum speed when the load is rejected. b. Parts of hydraulic turbines receiving water pressure shall be such that there is no risk of damage at the maximum water pressure when the load is rejected. 3-4-1-3 Article 86 1. Particularities of Equipment Prevention of Damage to Hydraulic Turbines Prevention of damages to hydraulic turbines Hydraulic turbines shall be installed so that there is no risk of serious damages when driftwood, floating debris and sediment flows in. 2. Prevention of vibration of hydraulic turbines and waterways Hydraulic turbines and waterways shall be installed in such a manner so as to cause no damage to the hydraulic turbines in operation due to the vibration thereof. Generator and turbines shall be provided with adequate GD2 to limit the maximum speed rise on full load rejection within permissible limits.(For details may refer to guidelines on Electro-mechanical equipment) _________________________________________________________________________________________________________________________________________ Page 54 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 87 1. Prevention of Damage to Pressure Tanks Prevention of damage to oil-pressure supply systems and compressed-air supply systems Oil-pressure supply systems and compressed-air supply systems to be installed in the Stations and HV and MV user’s sites shall be installed so as to avoid risks of damages as mentioned below. (1) Materials and the structure of the parts receiving pressure shall sufficiently withstand the maximum operation pressure and also shall be safe. (2) Parts receiving pressure shall be corrosion-resistant. (3) In the case where the pressure rises, the oil-pressure supply system and the compressed-air supply system shall have the function to reduce the pressure before the pressure reaches the maximum operation pressure. (4) The oil-pressure supply system and the compressed-air supply system shall have the function to detect any abnormal pressure in the early stage. (5) The oil-pressure supply system and the compressed-air supply system shall have the function to automatically restore the pressure when the pressure of the pressure tank drops. 2. Prevention of damage to gas-insulated equipment Gas insulated-equipment installed in the Stations and HV and MV user’s sites shall be installed as follows so as to avoid any risks of damage: (1) Materials and the structure of the parts receiving pressure shall sufficiently withstand the maximum operating pressure and also shall be safe. (2) Parts receiving pressure shall be corrosion-resistant. (3) Insulation gas shall not be inflammable, corrosive and hazardous. Article 88 Prevention of Damage to Bus Bars High-voltage and medium-voltage bus bars and connection conductors, and overhead ground wires to be installed in the Stations and HV and MV user’s sites shall be installed in accordance with the provisions of the following paragraphs and the provisions relevant to Section 3-5 and Section 3-6 so that there is no risk of damage. (1) Prevention of breaking of electrical conductors Electrical conductors, guys, overhead ground wires and other conductors to be installed for maintenance of electrical facilities shall be installed so that there is no risk of wires breaking under normal operations. (2) Prevention of damage to connecting parts in electrical conductors Connecting an electrical conductor to an electrical conductor and a power cable shall be carried out in such a manner so as not to increase the resistance of the electrical conductor, and to avoid risks of degradation of insulation performance (excluding bare conductors) and wire breakage under normal operations. (3) Prevention of collapse of supporting structures Materials and the structure of supporting structures for bus bars shall be installed in such a _________________________________________________________________________________________________________________________________________ Page 55 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) manner so as to avoid risks of collapse taking into consideration the lifting load due to electrical conductors supported by the supporting structure, wind pressure load by 35-50 m/s wind (depending upon the wind zone where equipment is installed) and the influences of the external environment such as change in climate, vibration and shocks, which is normally foreseeable at the place of installation. 3-4-2 Article 89 1. Protection, Monitoring and Control Systems Monitoring and Control Systems Monitoring and control Stations and control centers to remotely control and monitor them shall be installed in such a manner so as to continuously grasp and immediately control the status of the power system and electrical equipment in response to the change in the status and to stop the same safely and securely when any abnormality occurs. However, the same shall not apply to low-voltage hydropower electrical plants. 2. Classification of monitoring and control systems Monitoring and control systems to be applied to hydropower stations, substations and switching stations are classified into the following four (4) classes. (1) Continuous monitoring and control systems "Continuous monitoring and control system" means a system in which operators are stationed permanently in the Stations or their premises, and carry out monitoring and control of the electrical equipment of the Stations in the Stations or their premises. (2) Remote continuous monitoring and control systems "Remote continuous monitoring and control system" means a system in which operators are stationed permanently in a control center, and remotely carry out monitoring and control of the electrical equipment in the Stations from the control center. (3) Remote continuous monitoring and periodic control systems "Remote continuous monitoring and periodic control system" means a system in which operators are stationed permanently in a control center and remotely carry out monitoring of the electrical equipment in the Stations and, when it is necessary to operate the electrical equipment in the Stations, go to the Stations from the control center and operate the electrical equipment on site. (4) Periodic monitoring and control systems "Periodic monitoring and control system" means a system in which operators are stationed permanently in an office, and when it is necessary to monitor and operate the electrical equipment in the Station, go to the Station from the office and monitor and operate the electrical equipment on site. 3. Application of monitoring and control systems Monitoring and control systems provided for each kind of the Station stipulated in Table 89-1 shall be applied to the Stations. _________________________________________________________________________________________________________________________________________ Page 56 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 89-1 Application of monitoring and control systems Monitoring and control system Remote Remote continuous Continuous Continuous monitoring, and monitoring and monitoring and periodic control control system control system system Kind of Station Hydropower station Substation Switching station Switching station without circuit breaker Article 90 1. Periodic monitoring and control system Applicable Applicable --- --- Applicable Applicable Applicable Applicable --Applicable ----- Applicable Applicable Applicable Applicable Monitoring and Control Devices Measurement devices Stations and control centers shall be equipped with measurement devices provided for each kind of electrical facility and the installation points listed in Table 90-1 in order to continuously grasp the status of the power system at all times. However, the same shall not apply to low-voltage hydropower electrical plants. Table 90-1 Measurement devices Kind of electrical facility Gas-insulated switchgear Oil-pressure supply system Compressedair supply system Hydraulic turbine Generator Kind of Station Measurement device Hydro power station Substation Switching station Control center Pressure gauge ○ ○ ○ --- Pressure gauge ○ ○ ○ --- Pressure gauge ○ --- --- --- Bearing thermometer Reactive-power meter or power-factor meter Ampere meter or wattmeter Stator winding thermometer Bearing thermometer Voltmeter ○ --- --- --- ○ --- --- --- ○ --- --- ○ ○ --- --- --- ○ --- --- --- ○ --- --- --- Remarks _________________________________________________________________________________________________________________________________________ Page 57 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Kind of electrical facility Kind of Station Measurement device Hydro power station Substation Switching station Voltmeter ○*2 ○ --- ○ Ampere meter or wattmeter ○*2 ○ --- ○ Thermometer ○ ○ --- --- Ampere meter or reactive-power meter ○ ○ ○ --- Main transformer Reactive power compensator Bus bar Voltmeter ○ ○ ○ ○ Transmission line Ampere meter or wattmeter ○ ○ ○ ○ ○*3 ○*3 ○*3 ○ ○ ○ ○ --- ○ ○ --- ○ ○ ○ --- ○ ○ ○ --- ○ Distribution line Synchronism indicating system Bus-tie Oil-pressure tank Lubricating oil tank Sump tank DC control circuit Station service transformer Voltmeter with a maximum and minimum voltage indicator or voltage recorder Ampere meter or wattmeter Synchronism indicator Voltmeter Frequency meter Ampere meter or wattmeter ○ ○ ○ ○ Oil gauge ○ --- --- --- Voltmeter ○ ○ ○ --- ○ ○ ○ --- Ampere meter or wattmeter Remarks Control center Excluding cases where the voltage can be measured with measurement devices of the bus bar *2 In cases where the voltage can be measured with the measurement devices of the generator, installation is not required. *2 In cases where the voltage can be measured with the measurement devices of the generator, installation is not required. Limited to high-voltage transformers Excluding cases where the voltage can be measured with the measurement devices of the transformer or distribution line Excluding cases where monitoring can be carried out with the ampere meter or wattmeter of the transformer *3Incases where monitoring is carried out from the control center, installation is not required. Excluding cases where the synchronized parallel is not made Excluding cases where monitoring can be carried out with the ampere meter or wattmeter of the transformer _________________________________________________________________________________________________________________________________________ Page 58 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Kind of electrical facility Oil insulated equipment Wherever necessary Wherever necessary Kind of Station Measurement device Hydro power station Substation Switching station Control center Oil gauge ○ ○ ○ --- Watt-hour meter Reactive-power meter, power factor meter or reactive-power watt-hour meter ○ ○ ○ --- ○ ○ ○ --- Remarks [Notes] ○: Equips 2. Control systems Stations and control centers shall be equipped with control systems listed below in order to continuously control, quickly responding to a change in the status, and safely and securely stopping operation when any abnormality occurs. However, the same shall not apply to low-voltage hydropower electrical plants. (1) Monitoring and control systems for starting and stopping operation of hydraulic turbines and generators Hydropower stations and control centers shall be equipped with devices to operate and monitor the starting and stopping operation of hydraulic turbines and generators. (2) Load adjusting devices Hydropower stations and control centers shall be equipped with devices to adjust the load. However, the same shall not apply to cases where the inflow to the hydraulic turbine is fixed and the output is automatically limited. (3) Auto voltage regulators Devices to automatically regulate the voltage shall be installed in main transformers in the substations. (4) Monitoring and control systems of circuit breakers for controlling operations The Stations shall be equipped with devices to monitor the operation and switching of circuit breakers permanently necessary for operating generators, transformers, transmission lines, distribution lines and reactive power compensator. 3. Indication of alarms in control centers Hydropower stations, substations and switching stations to which continuous monitoring and control systems are not applied shall be equipped with devices that indicate the abnormality in the control center in accordance with Table 90-2, when any abnormality listed in Table 90-2 occurs. However, the same shall not apply to the Stations with periodic monitoring and control systems and low-voltage hydropower electrical plants. _________________________________________________________________________________________________________________________________________ Page 59 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 90-2 Indication of alarm in control centers Kind of Station Hydropower Substation Abnormality station When a hydraulic turbine stops automatically --○ When a circuit breaker necessary for operation ○ ○ automatically breaks When the temperature of the main transformer ○ ○ rises remarkably or the cooling device fails When the main transformer has trouble inside ○ ○ When the electrical circuit on the power source side in the main transformer has no voltage When the pressure of insulation gas in the gas-insulated equipment falls remarkably When the voltage of the control circuit falls remarkably When a fire breaks out in the Stations When the temperature of a shunt reactor rises remarkably or the cooling device fails Switching station --○ ----- --- ○ --- ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ [Notes] ○: Equips 4. Power supply devices for monitoring and control systems The Stations and control centers shall be appropriately equipped with power supply devices for station service transformers, storage batteries and rectifiers so that monitoring, control and communication can be carried out without trouble permanently. However, the same shall not apply to low-voltage hydropower electrical plants. Article 91 1. Protection Systems Installation of protection systems On necessary points in electrical circuits, protective devices such as power fuses, circuit breakers and protective relays that detect abnormalities and automatically break the electrical circuit shall be installed in order to stop operation safely, securely and quickly when any abnormality occurs. 2. Break-time For the break-time of circuit breakers and protective relays in electrical lines, a value equal to or smaller than the break-time in Table 91-1 shall be chosen so that there is no risk of breaking of electrical conductors, etc., safety of human bodies and other objects can be secured and the power system can be kept in stable status. Table 91-1 Break-time Classification High-voltage Medium-voltage SWER and single-phase system 3. Break-time 1 sec or less 2 sec or less 1 sec or less Rated value for switching devices Switching devices to be installed in the Stations and HV and MV user’s sites shall have the rated value corresponding to each duty listed below. _________________________________________________________________________________________________________________________________________ Page 60 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (1) Circuit breakers Circuit breakers to be installed in high-voltage and medium-voltage electrical circuits shall have the ability to switch the load current, exciting current and charging current that flows at the point where the circuit breaker is installed and shall have the ability to break a short-circuit current that flows at the point where the circuit breaker is installed. (2) Power fuses Power fuses to be installed in high-voltage and medium-voltage electrical circuits shall have the ability to break a short circuit current that flows at the point where the power fuse is installed. (3) Load switches Load switches to be installed in high-voltage and medium-voltage electrical circuits shall have the ability to switch the load current, exciting current and charging current that flows at the point where the load switch is installed. (4) Disconnecting switches Disconnecting switches to be installed in high-voltage and medium-voltage electrical circuits for switching the exciting current and charging current that flows at the point where the disconnecting switch is installed shall have the ability to switch these currents. Article 92 1. Protective Devices for Electrical Equipment Protective devices for hydraulic turbines and generators Hydraulic turbines and generators to be installed in hydropower stations shall be equipped with devices to break the generator from the electrical circuit and to stop the hydraulic turbine automatically as shown in Table 92-1, when any abnormality listed in Table 92-1 that causes significant damage and gives serious trouble to the supply of electricity occurs. Table 92-1 Protective devices for hydraulic turbines and generators Automatic stop Automatic device Classification Abnormality shutdown device *1 Low-voltage hydropower Over current --○ electrical plant Over current ○ ○ High-voltage and mediumvoltage hydropower electrical plant [Notes] *1: Over speed Remarkable temperature rise at bearings Generator internal fault Remarkable drop of oil pressure in pressure oil supply system and voltage of power supply to electric guide vane, electric needle, and electric deflector ○ ○ ○ ○ ○ ○ ○ ○ ○: Equips In the case of hydraulic turbines for which the flow rate is not regulated, if the flowing water can be intercepted within a time not to cause damage at the maximum runaway speed, it is not _________________________________________________________________________________________________________________________________________ Page 61 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) required to stop automatically. 2. Protection and alarm devices for transformers and reactive power compensator Transformers and reactive power compensator to be installed in Stations and HV and MV user’s sites shall be equipped with devices to automatically cut off the transformer and the reactive power compensator from the electrical circuit when any abnormality listed in Table 92-2 that might cause significant damage and serious trouble to the supply of electric power occurs, and other appropriate protection systems as shown in Table 92-2. Table 92-2 Protection systems for transformers and reactive power compensator Protection and alarm device Classification Abnormality Automatic Alarm shutdown device device Over current --○ ○ --- --- ○ --- ○ Over current or internal fault Over voltage or over current Internal fault ○ --- ○ --- ○ --- Over current ○ --- Internal fault Remarkable temperature rise ○ --- --- ○ --- ○ Internal fault Remarkable temperature rise Common Main transformer Transformer with cooling system (A cooling system in which the coolant is sealed-in for directly cooling the windings and iron core of the transformer and is forcibly circulated) Less than 15 MVA Power capacitor 15 MVA or more Common Shunt reactor Shunt reactor with cooling system (A cooling system in which the coolant is sealed-in for directly cooling the winding and iron core of the shunt reactor and is forcibly circulated) When the cooling system fails or when the temperature of the transformer rises remarkably When the cooling system fails or when the temperature of a shunt reactor rises remarkably [Notes] ○: Equips 3. Alarm device for gas-insulated devices Gas-insulated devices in which a drop in the pressure of the insulation gas might cause breakdown shall be equipped with devices that give alarm for drop in the pressure of the insulation gas. _________________________________________________________________________________________________________________________________________ Page 62 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 93 1. Protective Devices for Electrical Lines Protective devices for electrical lines At necessary points in electrical circuits, protective devices that detect earth faults and short circuit faults and automatically cut them off from the electrical circuit shall be installed. 2. Installation points on electrical circuits for circuit breakers (1) On the points listed below or points close to such points, devices to automatically break the electrical circuit when an earth fault and short-circuit fault occurs in the electrical circuit shall be installed. Outgoing points in the Stations (2) Receiving points in the Stations However, the same shall not apply to the Stations receiving electricity with one circuit and having no risk of reverse power flow. (3) Receiving points in the HV and MV user’s sites However, the same shall not apply when used in user’s sites receiving electricity with one circuit that are not connected to another user’s site and which consume all electricity received within the user's site. Article 94 Emergency Water Interception Devices Hydraulic turbines or waterways shall be equipped with devices that can intercept the inflow to the turbine cooperating with the hydropower civil engineering facilities. 3-4-3 Article 95 1. Earthing Arrangement Earthing Arrangement of Electrical Facilities Protective earthing Electrical facilities to be installed in the Stations and HV and MV user’s sites and low-voltage hydropower electrical plants shall be equipped with the protective earthings listed below so that there is no risk of rise of potential under abnormal conditions, harm to human bodies and damage to other objects due to electric shocks and fires caused by high-voltage invasion. (1) Earthing for exposed-conductive parts in electrical equipment Earthing work listed in Table 95-1 shall be provided for steel stands and metal cases of electrical equipment to be installed in electrical circuits according to the kind of the electrical equipment listed in Table 95-1. Table 95-1 Earthing of exposed-conductive parts in electrical equipment Kind of electrical equipment Kind of earthing work High-voltage electrical equipment Class A _________________________________________________________________________________________________________________________________________ Page 63 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Medium-voltage electrical equipment Low-voltage electrical equipment (Over 300V) Low-voltage electrical equipment (300V or lower) (2) Class A Class C Class D Earthing for facilities Facilities such as outdoor metal structures, external metal fences, protective metal fences and metal stands for operation shall be provided for earthing work in accordance with Item (1) depending on the kind of the electrical equipment to which such facility is installed. (3) Earthing for conductive parts in electrical equipment At necessary points in electrical circuits, the earthing listed below shall be provided. a. Earthing of instrument transformers Earthing work of Class A shall be provided at an arbitrarily chosen point in the electrical circuit on the secondary side of the high-voltage and medium-voltage instrument transformer. In cases where earthing work is provided for the electrical circuit on the primary side of a high-voltage and medium-voltage instrument transformer, earthing work of Class A shall be provided for. b. Earthing for station service transformers In cases where earthing is provided for in the electrical circuit on the secondary side of transformers connecting a medium-voltage electrical circuit and a low-voltage electrical circuit, earthing work of Class B shall be provided for. A "low-voltage electrical circuit" means an electrical circuit that supplies electricity to automatic control circuits, remote control circuits, signal circuits for remote monitoring devices, and the like. c. 2. Earthing for stabilizing windings and idle windings in transformers In cases where earthing is provided for stabilizing windings and idle windings in high-voltage and medium-voltage transformers, earthing work of Class A shall be provided for. Earthing for neutral points in high-voltage and medium-voltage electrical circuits In cases where earthing is provided for on the neutral point of high-voltage and medium-voltage electrical circuits in the Stations and HV and MV user’s sites in order to secure reliable operation, to suppress abnormal voltage and to reduce the voltage to ground for protective devices of electrical circuits, the earthing electrode shall be installed so as to avoid risks of danger to the human bodies, domestic animals and other facilities due to potential difference generated between the pole and the nearby ground when any failure occurs. 3. Earthing on earth-return side of SWER In cases where electrical equipment for SWER are installed in hydropower stations and substations, earthing for electrical equipment for SWER shall be provided for so as to avoid risks of danger to the human bodies, domestic animals and other facilities due to the potential difference between the electrical equipment and the nearby ground caused by load current and when any failure occurs. 4. Earthing for surge arresters _________________________________________________________________________________________________________________________________________ Page 64 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The resistance to earth of earthing provided for surge arresters for high-voltage and medium-voltage electrical circuits in Stations and HV and MV user’s sites shall be lower than ten (10) ohms as much as possible so as not to hinder the functions of the surge arrester. 5. Earthing for lightning guards The resistance to earth of the earthing provided for lightning guards such as overhead ground wires and lightning rods to be installed in Stations and HV and MV user’s sites shall be not greater than ten (10) ohms. However, in cases where overhead ground wires are used as SWER, Paragraph 3 shall apply to earthing work of the overhead ground wire. Article 96 1. Particularities of Earthing Arrangement Earthing conductors For earthing conductors to be installed in electrical circuits in Stations and HV and MV user’s sites, metal wires that do not corrode easily and can safely conduct the electric current when any failure occurs shall be used and installed so as to avoid risks of damage. (1) Mechanical strength of earthing conductors In order to secure necessary mechanical strength, earthing conductors listed in Table 96-1 shall be used depending on the kind of earthing work for which the earthing conductor is used. Table 96-1 Earthing conductors for earthing work Kind of earthing conductor Metal wire Annealed copper wire Annealed copper twisted wire Tensile strength Diameter Sectional area Earthing conductors for neutral points of high-voltage and medium-voltage electrical circuits in generators and transformers 3 kN or more 4 mm or more 14 mm2 or more Others 2 kN or more 3 mm or more 6 mm2 or more Low-voltage side neutral points of transformers transforming mediumvoltage into low voltage 2 kN or more 3 mm or more 6 mm2 or more 1 kN or more 2 mm or more 4 mm2 or more Kind of earthing work Class A Class B Class C and Class D (2) Thermal strength of earthing conductors Earthing conductors in which earthing current flows when any abnormality occurs such as those for earthing for neutral points of electrical equipment and high-voltage and medium-voltage electrical circuits shall be installed taking into consideration earthing current during the occurrence of such abnormality and the duration of failures in addition to mechanical strength in Item (1). 2. Installation of earthing conductors Earthing conductors for instrument transformers, neutral points, surge arresters and SWER to be installed in the Stations and HV and MV user’s sites shall be earthed directly to the ground without connecting to stands of equipment. _________________________________________________________________________________________________________________________________________ Page 65 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Bare live parts of earthing conductors shall be installed so that there is no risk of operators contacting them easily. 3. Neutral earthing devices Resistances and reactors to be connected to earthing conductors in the Stations and HV and MV user’s sites shall be such that the electric current that flows when any failure occurs can be safely applied. Bare live parts of resistors, reactors and other neutral earthing devices shall be installed so that there is no risk of operators contacting them easily. 4. Prohibition against installation of switching devices on earthing conductors for neutral No switching device and power fuse, excluding circuit breakers to be installed to switch neutral resistances and neutral reactors, shall be installed on earthing conductors for neutral in Stations and HV and MV user’s sites. 5. Connection between earthing conductors In cases where earthing conductors to be installed in the Stations and HV and MV user’s sites fall under any of the following items, they shall not be connected to earthing conductors of other electrical equipment. (1) Earthing conductors to be installed on earth-return side earthing of SWER (2) Earthing conductors to be installed on external fences in accordance with the provisions of Article 69 6. Clear indication of the points to measure resistance to earth On appropriate places in Station and HV and MV user’s sites, points to measure resistance to earth shall be provided for and clearly indicated. 3-5 Transmission Lines 3-5-1 Overhead Transmission Conductors Article 97 1. Properties of Electrical Conductors Minimum Tensile Strength Overhead transmission conductors, including overhead ground wires but excluding the case where they are cables, shall be stranded wires with a tensile strength no less than 10 kN. 2. Bare Conductors Bare conductors and overhead ground wires (including overhead ground wires containing optical fiber cable) that are used for transmission lines shall conform to the following requirements: (1) Properties of Solid Wires Solid wires (hard-drawn copper wire, hard-drawn aluminum wire, galvanized steel wire, _________________________________________________________________________________________________________________________________________ Page 66 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) aluminum-clad steel wire, aluminum alloy wire, etc.) which compose an electrical conductor shall have the conductivity and tensile strength not lower than the values specified in the IEC standards (e.g., IEC60028, IEC60889, IEC60888, IEC61232 and IEC60104). The tensile strength of hard-drawn copper wires shall conform to Table 97-1. Diameter of solid wire (mm) No less than 0.4 but no more than 12.0 Table 97-1 Tensile strength (N/mm2) No less than (462-10.8d) d: Diameter of solid wire (mm) (2) Tensile Strength of Stranded Wire a. Single stranded wire (Electrical conductor composed of solid wires of the same kind) The tensile strength of a single stranded wire shall be the sum of the tensile strength of the solid wires. b. Composed stranded wire with steel solid wire and other solid wires The tensile strength of a stranded wire composed of steel solid wires and other kinds of solid wires shall be the sum of the total tensile strength of non-steel solid wires and the total tensile strength of steel wires at 1% elongation. 3. 4. Insulated Conductors Insulated conductors shall be used for transmission conductors with a voltage of up to 35 kV and have the properties that conform to Paragraph 3 of Article 144. Cables Properties of cables shall conform to the provisions of Article 124. Article 98 1. Load on Overhead Transmission Conductors and Safety Factor Assumed Load and Safety Factor Overhead transmission conductors and overhead ground wires (excluding cables, the same applies hereafter in this article) shall be installed with the tension to allow a safety factor specified in the following Item (2) when they are subject to the assumed load specified in the following Item (1) below at the average temperature in the area. (1) Assumed Load The assumed load for the calculation of tension of overhead transmission conductors and overhead ground wires shall be the composite load of the vertical loads specified in the following item a. and the horizontal loads specified in the following item b. a. b. (2) The vertical load shall be the weight of the electrical conductor. The horizontal load shall be the horizontal wind pressure load of 790 N per 1 m2 of vertical projected area of the electrical conductor. Safety Factor A safety factor of no less than 2.5 shall be applied to the tensile strength (ultimate tensile strength; breaking strength) of overhead transmission conductors and overhead ground wires. 2. Prevention of Damage due to Slight Wind Oscillation _________________________________________________________________________________________________________________________________________ Page 67 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Overhead transmission conductors and overhead ground wires shall be installed so as not to suffer damage from a slight wind oscillation. 3. Installation of Overhead Cables Installation of overhead cables shall be based on Item 2 of Paragraph 3 of Article 145. Article 99 1. Jointing and Branching of Electrical Conductors Jointing of Bare Conductors Where bare conductors for overhead transmission lines are jointed with each other or with insulated conductors or cables, they shall conform to the following requirements: (1) The electric resistance of a joint shall not exceed that of a length of the used electrical conductor equal to that of the joint. (2) The tensile strength of the electrical conductors shall not be reduced by 5% or more. However, this requirement shall not apply to cases where jumper conductors are connected and the tension applied to other electrical conductors is substantially smaller than the strength of the electrical conductors. (3) The electrical conductors shall be jointed using jointing sleeves and other tools. (4) 2. Where copper conductors are jointed with aluminum conductors, care shall be exercised not to generate electrochemical corrosion in the joint. Jointing of Insulated Conductors Where insulated conductors for overhead transmission conductors are jointed with each other or with cables, they shall conform to the provisions of the preceding Paragraph 1. The joint shall be fully covered with material that has the same insulating effect as the insulated conductor or with a greater effect, except where the electrical conductors are jointed using a jointing tool that has the same insulating effect as the insulator of the electrical conductors or with a greater effect. 3. Jointing of Overhead Cables Where cables for overhead transmission conductors are jointed with each other, they shall conform to Items (1) and (4) of Paragraph 1 and a junction box and other tools shall be used. 4. Jointing of Overhead Ground Wires Overhead ground wires (including the distribution conductors of SWER systems installed at the top of a steel tower) shall be jointed according to the Items (1), (2) and (3) of Paragraph 1. 5. Branching of Overhead Conductors Overhead transmission conductors shall be branched at a supporting point of the electrical conductors except for such cases where the electrical conductors are installed so that no tension is applied to the electrical conductors at the branch point. 3-5-2 Insulator for Overhead Transmission Lines Article 100 Mechanical Strength of Insulators for Overhead Transmission Lines _________________________________________________________________________________________________________________________________________ Page 68 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 1. Assumed Load The assumed loads to be used for calculating the strength of insulator devices for overhead transmission lines shall conform to the following requirements: (1) Vertical Load The vertical load shall be the sum of the weight of electrical conductors, the weight of insulator devices and the vertical component of force generated by the assumed maximum tension of the electrical conductors. (2) Horizontal Transverse Load The horizontal transverse load shall be the sum of the wind pressure loads of electrical conductors and insulator devices and the horizontal component of load generated by the assumed maximum tension of the electrical conductors. The wind pressure loads shall be calculated based on the values listed in Table 100-1. Table 100-1 Subject to wind pressure Multiple conductors *1 Single conductors Insulator device Electrical conductor Wind pressure per 1 m2 of vertical projected area (N) 710 790 1100 *1: This applies only to cases where two compositional conductors are arranged horizontally and the distance between such electrical conductors is no more than twenty times their outer diameter. (3) Assumed Maximum Tension of Transmission Conductors The assumed maximum tension of transmission conductors shall be the tension of the transmission conductor under the composite load of the vertical load generated by the weight of the electrical conductor and the horizontal load generated by the horizontal wind pressure stipulated in Table 100-1 at the average temperature in the area. 2. Safety Factor A safety factor of no less than 2.5 shall be applied to the insulator devices for overhead transmission lines. The safety factor mentioned above shall be obtained as follows: (1) (2) Tension insulator device (Insulator device that anchors electrical conductors) [Safety factor] = [Tensile break strength] / [Assumed maximum tension at a support point] Suspension insulator device (Insulator device that electrical conductors are hung from) [Safety factor] = [Tensile break strength] / [Composite load of vertical load and horizontal transverse load] (3) Supporting insulator device [Safety factor] = [Bending break strength] / [Horizontal transverse load or vertical load applied perpendicular to the axis of the insulator device] 3-5-3 Dielectric Strength of Overhead Transmission Lines _________________________________________________________________________________________________________________________________________ Page 69 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 101 Clearance between Supporting Structures and Electrical Conductors The clearance between overhead transmission conductors (excluding cables) and their supporting structures, cross arms or guys (pole braces) shall not be smaller than the values shown in Table 101-1 even when the electrical conductor sways by a wind velocity of about 20m/s. Table 101-1 Nominal voltage No higher than 35 kV 115 kV 230 kV 500 kV Clearance (*1) No less than 70 cm No less than 145 cm No less than 270 cm (*1) As per Item (1) of Paragraph 3 in Article 149 Article 102 1. Dielectric Strength of Overhead Transmission Lines Dielectric Strength of Insulators The insulators to be used for overhead transmission lines shall have the dielectric strength that has been verified in the wet power-frequency voltage test specified in IEC60383-1 or other tests equivalent to IEC. 2. Dielectric Strength Test Where the operational voltage to ground is applied between the overhead transmission line and the ground continuously for ten (10) minutes to test the dielectric strength (the normal voltage-to-ground test in Paragraph 3 of Article 56) before the commencement of operation, the transmission line shall withstand such a test. In case where cables are used for overhead transmission lines, the test shall conform to Article 123. 3-5-4 Article 103 1. Supporting Structures Steel Structural Members of Supporting Structures Fundamental Properties Flat steel, shaped steel, steel pipes, steel plates, steel bars and bolts which compose a steel tower or iron pole used for overhead transmission lines shall be appropriate ones as specified in ISO (International Organization for Standardization), ASTM (American Society for Testing and Material) and JIS (Japanese Industrial Standard) or other standards equivalent to these standards. 2. (1) Thickness of Steel Members and so on Shaped steel, steel pipes and steel plates to be used for a steel tower or iron pole for overhead transmission lines shall have the thickness and other dimensions specified below: Minimum thickness of shaped steel a. Those to be used as a main post member of an iron pole (in which a main member of a cross arm is included; The same shall apply hereafter in this article) shall have the thickness of 4 mm. _________________________________________________________________________________________________________________________________________ Page 70 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (2) (3) b. Those to be used as a main post member of a steel tower shall have the thickness of 5 mm. c. Those to be used as other structural members shall have the thickness of 3 mm. Minimum thickness of steel pipes a. Those to be used as a main post member of an iron pole shall have the thickness of 2 mm. b. Those to be used as a main post member of a steel tower shall have the thickness of 2.4 mm. c. Those to be used as other structural members shall have the thickness of 1.6 mm. Slenderness ratio of steel members The slenderness ratio of a compression member shall be no more than 200 for those to be used as a main post member and no more than 220 for compression members other than main post members (excluding those used as auxiliary members) and no more than 250 for those used as auxiliary members. (4) Minimum thickness of steel plates The thickness shall be no less than 1 mm. 3. Strength of Steel Members and Bolts Steel members and bolts to be used for a steel tower or an iron pole of overhead transmission lines shall have the strength as specified in Table 103-1. Table 103-1 Classification of strength When Y 0.7B Tensile strength When Y > 0.7B Compression strength Flexural strength When Y 0.7B Shearing strength When Y > 0.7B Bearing strength Buckling strength 0 < k < k Strength Y 0.7B Y Y Y / 3 Y K 0 K1 k 0.7B / 3 1.65Y E Y K2 k E Y 2 1.52E / 2.2k2 Where Y: B: k: Lk: r: E: Yield point strength of steel members and bolts Tensile strength of steel members and bolts Effective slenderness ratio ( = Lk / r ) Effective buckling length of steel members Turning radius of a steel member cross section Elastic modulus (20.6 102 N/m2) _________________________________________________________________________________________________________________________________________ Page 71 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 15 . E 2.2 KY : K, K0, K1, K2: Refer to Table 103-2. Table 103-2 Structural members with little decentering (steel pipe, cruciform section plate, etc.) Structural members with a little decentering (angle steel used for a main post member, etc.) Structural members with significant decentering (angle steel used for a web member with one side flange joint, etc.) (*) K K0 K1 K2 0.6 1 0 0.352 0.5 0.945 0.0123 0.316 0.3 0.939 0.424 0 (*) Note that the buckling strength shall be no more than 0.6Y for structural members with significant decentering. 4. Strength of Reinforced Concrete Pole Components Components of a reinforced concrete pole for overhead transmission lines shall have the strength as specified below: (1) Strength of concrete The strength of concrete at yield point shall be based on the design standard strength (4-week strength; Fc) of concrete and conform to Table 103-3. Table 103-3 ×106N/m2 Compression strength Fc/2 Tensile strength Fc/20 Shearing strength (2) Fc/20 and 0.74+1.5Fc/100 Bond strength of concrete The bond strength of concrete at yield point shall be based on the design standard strength (4-week strength; Fc) and conform to Table 103-4. Table 103-4 ×106N/m2 Bending member Upper edge round bar Round bar Deformed round bar Shaped steel (3) 6Fc/100 and no more than 1.32 Fc/10 and no more than 1.32+3Fc/75 Normal round bar Fixative joint 9Fc/100 and no more 6Fc/100 and no more than than 1.99 1.32 3Fc/20 and no more Fc/10 and no more than than 99+3Fc/50 1.32+3Fc/75 3Fc/100 and no more than 0.66 Strength of shaped steel, flat steel and steel bars The strength of shaped steel, flat steel and steel bars at yield point shall conform to Table 103-5. Table 103-5 _________________________________________________________________________________________________________________________________________ Page 72 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Y and no more than 234 Y and no more than 294 Yield compression strength (N/mm2) Y and no more than 234 Y and no more than 294 Y Y Y and no more than 322 Y and no more than 322 Y and no more than 0.7B Y Yield tensile strength (N/mm2) Round bar Diameter ≥ 29 mm 29 mm > Diameter > 25 mm 25 mm ≥ Diameter Deformed round bar Others Y: B: Strength of material at yield point Tensile strength of material (4) Strength of bolts The strength of bolts shall conform to Table 103-1. Article 104 1. Loads on Supporting Structures and Safety Factor Types and Combinations of Assumed Loads (1) Types and combinations of assumed loads to be used for calculating the strength of supporting structures for overhead transmission lines shall conform to the following provisions: The loads specified in Table 104-1 shall be used in the combinations shown in Table 104-2 depending on the classification and type of supporting structure. Table 104-1 Type load of Vertical load Horizontal transverse load Horizontal longitudinal load Contents Symbol The load applied by the weight of the supporting structure (including cross arms) The load applied by the weight of strung wires and insulator devices If the electrical line has a remarkable vertical angle, the vertical load from the line shall be added. If guys are used (in case of a steel tower, this shall be limited to a temporary electrical line specified in Paragraph 2 in Article 107), the load by a vertical component of force generated by tension of the guys shall be added. Wind pressure load applied to the supporting structure (including cross arms) Wind pressure load applied to strung wires and insulator devices The load by a horizontal transverse component of force generated by the assumed maximum tension of strung wires when the electrical line has a horizontal angle The load by a torsional force stress generated by cutting strung wires Wind pressure load applied to the supporting structure (including cross arms) The load by a horizontal longitudinal component of unbalanced tension of strung wires The load by a horizontal longitudinal component of unbalanced tension generated by cutting strung wires The load by a torsional force stress generated by cutting strung wires Wt Wc Ws Ht Hc Ha q H 't P1 P2 q1 Where, strung wires mean electrical conductors and overhead ground wires. (The same applies hereafter in this standard.) _________________________________________________________________________________________________________________________________________ Page 73 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 104-2 Classification Type of of supporting supporting structure structure Load condition Class A reinforced concrete pole All types Wind pressure load All types Wind pressure load and vertical load Class A iron pole Class B reinforced concrete pole Common type Assumed normal load Anchor type Assumed normal load Strain type Assumed normal load Class B iron pole Common type Assumed normal load Assumed abnormal load Steel tower Anchor type Assumed normal load Assumed abnormal load Assumed normal load Strain type Assumed abnormal load Note: Wind direction Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular or 60 to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Perpendicular to the electrical line Parallel to the electrical line Combination of assumed loads Horizontal Horizontal Vertical load transverse load longitudinal load Wt Wc Ws Ht Hc Ha q H’t P1 P2 q1 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Circles indicate the assumed loads to be considered at the same time. The wind direction that brings the bigger assumed load should be selected. The supporting structures in Table 104-2 shall have the following types: a. Anchor type Supporting structure for use of anchoring all strung wires _________________________________________________________________________________________________________________________________________ Page 74 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. Strain type Supporting structure for use of reinforcing the linear parts of electrical lines or use in a place where there is a large difference in the span at both sides of the supporting structure c. Common type Supporting structures, excluding above a and b, with tension type or suspension type insulator devices (2) Where strung wires are arranged asymmetrically on the supporting structure, the assumed vertical eccentric load shall be added to the load in Table 104-2, and the load by normal torsional load shall also be added for anchor or strain type. 2. Wind Pressure Load (1) Wind Pressure Values The wind pressure load used for Paragraph 1 of this Article 104 shall be the value obtained by calculation based on the wind pressure specified in the following Table 104-3. This shall not apply when calculation is made based on values obtained by a wind pressure (wind duct) test using a wind at a velocity of not less than 35 m/s. The wind receiving area shall be the vertical projected area of the structural member. For cross arms of a concrete pole, an iron pole except a columnar pole, and a steel tower, the wind receiving area shall be the vertical projected area of the front structures that receive the wind. Table 104-3 Subject to the wind pressure Iron pole Supporting structure Columnar pole Triangle or rhombic pole Square pole consisting of steel pipes Others Reinforced concrete pole Columnar pole Others Shaped steel tower Steel pipe tower Steel tower Columnar pole Single Hexagonal or pole octagonal pole Electrical wires forming multiple conductors (Limited to those in which two compositional Electrical conductors are arranged horizontally and the conductors distance between such electrical conductors is and other no more than 20 times their outer diameter) strung wires Others Insulator device Cross arms for an iron pole (limited to a columnar pole) and a Wind pressure to 1 m2 of the vertical projected area of the structural member (N) 630 1,500 1,180 1,740 when the web members overlap in the front and the back 1,890 in other cases 630 950 2,290 1,350 630 1,180 710 790 1,100 1,260 when it is used as a single member _________________________________________________________________________________________________________________________________________ Page 75 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) reinforced concrete pole (2) 1,740 in other cases Wind pressure load at an oblique wind When the wind blows to the electrical line at an angle of 60, the wind pressure load in an assumed normal load of a common type steel tower shall be that calculated by the wind pressure load multiplier (in case of a square tower) in Table 104-4. Table 104-4 The multiplier to the wind pressure load when the wind blows perpendicular to the electrical line (in case of a square tower) 1.6 Classification of wind pressure load Wind pressure load to steel tower Wind pressure load to body Shaped steel tower Steel pipe tower 1.4 0.5 (for the wind pressure in the direction of the electrical line) 0.75 Wind pressure load to cross arm Wind pressure load to strung wire (3) Augmentation of wind pressure by the height a. Steel tower The wind pressure of a shaped steel tower or steel pipe tower that is higher than 40 m shall conform to Table 104-5. N/m2 Table 104-5 Height No higher than 50 m No higher than 60 m No higher than 70 m No higher than 80 m b. Shaped steel tower Below No less than 230kV 230kV 2,450 2,610 2,610 2,760 2,920 3,080 Steel pipe tower Below 230kV No less than 230kV 1,430 1,500 - 1,500 1,580 1,660 1,740 Wires and insulators When a steel tower is higher than 80 m, the wind pressure shall be calculated by increasing the wind velocity appropriately. 3. Unbalanced Tension and so on Unbalanced tension and so on used in Paragraph 1 of this Article 104 shall conform to the following requirements: (1) The unbalanced tension and the torsional force shall conform to Table 104-6. Table 104-6 _________________________________________________________________________________________________________________________________________ Page 76 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Classification of supporting structure Type of supporting structure Common type Anchor type Steel tower Strain type Common type Class B iron reinforced concrete pole and Class B iron pole Anchor type Strain type (2) (3) Unbalanced tension and torsional force Assumed normal load Assumed load abnormal No specification Horizontal longitudinal component of force of the unbalanced tension equal to the assumed maximum tension for each strung wire Horizontal longitudinal component of force of the unbalanced tension equal to 1/3 of the assumed maximum tension for each strung wire Horizontal longitudinal component of force of the unbalanced tension generated by cutting strung wires and torsional force No specification Horizontal longitudinal component of force of the unbalanced tension equal to the assumed maximum tension for each No specification strung wire Horizontal longitudinal component of force of the unbalanced tension equal to 1/3 of the assumed maximum tension for each strung wire For steel towers, the strung wires shall be cut according to the following requirements depending on the total number of phases of electrical conductors (which means phases for each circuit; The same shall apply hereafter). a. The overhead ground wire shall not be cut at the same time as the electrical conductors and only one wire shall be cut. b. Where the total number of phases of electrical conductors is no more than twelve (12), one phase that maximizes the stress generated in each structural member (Two electrical conductors from one phase in case of multiple conductors for steel towers other than anchor type) c. Where the total number of phases of electrical conductors is over twelve (12) (excluding the case specified in the following Item d.), two phases in different circuits that maximize the stress generated in each structural member (Two electrical conductors from one phase in case of multiple conductors for steel towers other than anchor type) d. Where electrical conductors are arranged so that nine or more phases are in a longitudinal row and two phases are in a transverse row, one of the top six phases in the longitudinal row (two electrical conductors from one phase in case of multiple conductors for steel towers other than anchor type) and one phase from the other phases (two electrical conductors from one phase in case of multiple conductors for steel towers other than anchor type) that maximize the stress generated in each structural member. The unbalanced tension generated by cutting the strung wire shall be equal to the assumed maximum tension. Provided, however, that the unbalanced tension may be 0.6 times the assumed maximum tension if, depending on the mounting method of the strung wire, the supporting point of the strung wire shifts when the wire is cut or the strung wire slides at the supporting point. 4. Safety Factor of Supporting Structure _________________________________________________________________________________________________________________________________________ Page 77 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The yield strength of the structural members of reinforced concrete poles, iron poles and steel towers used for overhead transmission lines shall satisfy the safety factor listed in Table 104-7 for the assumed loads specified in Paragraph 1 to Paragraph 3. Classification of supporting structure Class A reinforced concrete pole Class A iron pole Class B reinforced concrete pole Class B iron pole Steel tower Table 104-7 Load condition Wind pressure load Wind pressure load Vertical load 1. 1.65 Assumed normal load 1.65 Assumed normal load 1.65 1.1 (1.65 for cross arms) Assumed abnormal load Article 105 Safety factor 1.65 Loads on Foundations of Supporting Structures and Safety Factor Loads on the Foundation of a Supporting Structure The loads applied to the foundation of a supporting structure for overhead transmission lines shall be calculated from combinations of the assumed loads of the supporting structure specified in Article 104 and the resultant maximum values shall be the assumed normal and abnormal loads for the foundation. 2. Safety Factor of the Foundation The safety factor of the foundation of a supporting structure for overhead transmission lines shall satisfy the value listed in Table 105-1 for its yield strength. This shall not apply when the installation is carried out according to Items (2) or (3) of Paragraph 1 in Article 151. Table 105-1 Classification of supporting structure 3. Safety factor Assumed normal load Assumed abnormal load Reinforced concrete pole and iron pole 2.0 - Steel tower 2.0 1.33 Treatment of the Weight of the Foundation The weight of the foundation used for calculating the safety factor shall be treated in accordance with the following provisions: (1) For the foundation subject to a lifting load, two-thirds or less of the weight of the foundation (or the weight of the foundation of a steel tower to an abnormal load) may be included in the lift bearing power. (2) For the foundation subject to a compressive load, the weight of the foundation shall be included in the compressive load. Article 106 1. Reinforcement of Overhead Transmission Lines Class A Reinforced Concrete Poles and Class A Iron poles _________________________________________________________________________________________________________________________________________ Page 78 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Where five or more Class A reinforced concrete poles or Class A iron poles used for overhead transmission lines are installed successively in a straight portion (including portions with a horizontal angle of five degrees or less), such poles shall be installed according to the following requirements: (1) For every five poles or less frequently, guys shall be installed on both sides of wires in the direction perpendicular to the electrical line. The same shall not apply when voltage of 35 kV or below is used. (2) Where 15 or more of such poles are used successively, guys shall be installed on both sides of wires in the direction of the electrical line for every 15 poles or less. (3) 2. The guys installed according to Item (1) and Item (2) can be used in common with the guys installed according to the provisions of Paragraph 1 of Article 107. Class B Reinforced Concrete Poles or Class B Iron poles 3. Where ten or more Class B reinforced concrete poles and Class B iron poles with suspension insulator devices are used successively, one iron reinforced concrete pole or iron pole of strain type shall be installed for every ten poles or less frequently. Steel Tower Where ten or more steel towers with suspension insulator devices are used successively, one steel tower with a strain-type suspension insulator or one steel tower with a suspension insulator device shall be used for every ten towers or less frequently. Such a suspension insulator device shall be designed assuming that the magnitude of unbalanced tension generated by cutting a strung wire is the value equal to the assumed maximum tension of the strung wire when the assumed abnormal load is determined. Article 107 1. Reinforcement by Guys Installation of Guys for Class A Reinforced Concrete Poles, Class A Iron poles, Class B Reinforced Concrete Poles and Class B Iron poles Guys for Class A reinforced concrete poles, Class A iron poles, Class B reinforced concrete poles and Class B iron poles used for overhead transmission lines shall be installed according to Paragraphs 1 and 3 of Article 152. 2. Installation of Guys for Steel Towers Steel towers used for overhead transmission lines shall have no guys that share the strength of the towers. However, steel towers to be used temporarily within six months may be equipped with guys. In this case, the guys shall be installed according to Item (1) of Paragraph 1 of Article 152. 3. Safety Factor and Specification of Guys Guys used for reinforced concrete poles, iron poles and steel towers shall conform to Paragraph 2 in Article 152. 3-5-5 Regulations for Installation Article 108 Clearance between Overhead Ground Wires and Electrical Conductors The clearance between any overhead ground wire (including the distribution conductors of SWER systems installed at the top of a steel tower) and any transmission conductor in a place _________________________________________________________________________________________________________________________________________ Page 79 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) other than supporting points shall be larger than the clearance at supporting points. Article 109 1. Height of Overhead Transmission Conductors and Limitation of Span Height of Overhead Transmission Conductors The height of overhead transmission conductors shall conform to the following provisions, and the height shall be secured in case of the electrical conductor dip at the maximum design operating temperature. (1) Height of overhead transmission conductor above the ground surface The height of an overhead transmission conductor above the ground surface (above the road when the overhead transmission conductor crosses a pedestrian crossing bridge) shall be no less than the value specified in Table 109-1. Table 109-1 Height above the ground surface Nominal voltage Common place No higher than 35 kV Higher than 35 kV (2) Crossing a road 5.5 m 6m Value obtained by adding 6 cm for each 10 kV over 35 kV and fraction thereof to 5.5 m Value obtained by adding 6 cm for each 10 kV over 35 kV and fraction thereof to 6 m Crossing a pedestrian crossing bridge 5.5 m (4 m in case of an insulated conductor or cable) Value obtained by adding 6 cm for each 10 kV over 35 kV and fraction thereof to 5.5 m An area such as a mountainous district where persons do not have easy access 5m Value obtained by adding 6 cm for each 10 kV over 35 kV and fraction thereof to 5m Height of overhead transmission conductor above a water surface Where overhead transmission conductors are installed above a water surface, the height of the electrical conductors above the water surface shall be no less than the values specified in Table 109-2. Table 109-2 No craft passage Having craft passage From the craft's mast on the From the highest water level highest water level 5m 2m Value obtained by adding 6 cm Value obtained by adding 6 cm for each 10 kV over 35 kV and for each 10 kV over 35 kV and fraction thereof to 5 m fraction thereof to 2 m Nominal voltage No higher than 35 kV Higher than 35 kV 2. Limitation of Span (1) The span length of overhead transmission lines shall be no longer than the values specified in Table 109-3. Table 109-3 Classification of supporting structure Class A iron pole or class A reinforced concrete pole Class B iron pole or class B reinforced concrete pole Span 150 m 250 m _________________________________________________________________________________________________________________________________________ Page 80 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Steel tower (2) 600 m Where stranded wires with a tensile strength no less than 30 kN are used for electrical conductors, the provisions of the preceding paragraph are not necessarily adhered to if the supporting structures are installed in accordance with the following provisions. In this case, the span length of such electrical conductors shall be no longer than 300 m when class A iron poles or class A reinforced concrete poles are used, and no longer than 500 m when class B iron poles or class B reinforced concrete poles are used. a. Class A iron poles or class A reinforced concrete poles shall be equipped with guys on both sides of each strung wire in the direction of the electrical line. Such guys shall withstand the horizontal force caused by the unbalanced tension equivalent to 1/3 the assumed maximum tension of the strung wire. The same shall not apply where the guy is installed on the supporting structure in a place adjacent to the span of the electrical line depending on terrain conditions. b. Strain type iron poles or reinforced concrete poles shall be used as class B iron poles or class B reinforced concrete poles or such poles shall be equipped with the guys in accordance with the provisions of item a) above. The same shall not apply where such iron poles or reinforced concrete poles are used or such guys are installed for the supporting structure in a place adjacent to the span of the electrical line depending on terrain conditions. c. Strain type steel towers shall be used as steel towers. The same shall not apply where strain type steel towers are used for the supporting structure at a place adjacent to the span of the electrical line depending on terrain conditions. Article 110 Clearance between Plants and Overhead Transmission Conductors The clearance between any overhead transmission conductor and any plant shall be no less than the value specified in Table 110-1. The clearance shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature or sways in the wind. Table 110-1 Nominal voltage No higher than 35 kV Higher than 35 kV Clearance 2m The value obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to 2 m This shall not apply when overhead transmission lines are installed according to the following requirements: (1) Overhead transmission conductors with a voltage no higher than 35 kV, for which insulated conductors are used, shall be installed so as not to contact plants. (2) Overhead transmission conductors with a voltage no higher than 130 kV, for which cables are used, shall be installed so as not to contact plants. Article 111 Restrictions in Urban Areas 1. Prohibition of Installation in Urban Areas No overhead transmission line shall be installed in urban areas or other densely built-up areas. 2. Relaxation of Restrictions Paragraph 1 shall not apply where the nominal voltage of the overhead transmission line is no more than 130 kV and the electrical conductors are cables or the installation is carried out _________________________________________________________________________________________________________________________________________ Page 81 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) according to the following requirements: (1) Strength of electrical conductor The strength of electrical conductor shall conform to Table 111-1. Table 111-1 Nominal voltage Strength of electrical conductor No higher than 35 kV Stranded wire with a tensile strength no less than 30 kN Higher than 35 kV but no higher than Stranded wire with a tensile strength no less than 40 130 kV kN (2) Limitation of span The length of span of overhead transmission lines shall conform to Table 111-2. Table 111-2 Classification of supporting structure Class A reinforced concrete pole or class A iron pole Class B reinforced concrete pole or class B iron pole No longer than 75 m No longer than 150 m No longer than 400 m (or no longer than 250 m when two or more electrical conductors are arranged horizontally and the distance between the electrical conductors is less than 4 m) Steel tower (3) Length of span Shutoff time Overhead transmission lines with a nominal voltage higher than 35 kV shall be equipped with devices that automatically shut off the electrical circuit within one second after an earth fault or short circuit occurs in the electrical circuit. (4) Height of electrical conductor above the ground The height of overhead transmission conductors above the ground shall be no less than the value specified in Table 111-3. The height shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature. This shall not apply to overhead transmission lines for a span connecting the yard of a power plant, substation or similar place to the outside. Nominal voltage No higher than 35 kV Higher than 35 kV (5) Table 111-3 Height of electrical conductor above the ground 10 m (8 m when insulated conductors are used) Value obtained by adding 6 cm for each 10 kV over 35 kV and fraction thereof to 10 m Indication of danger Supporting structures shall be provided with an indication of danger in a location where it is easily read. This shall not apply when insulated conductors are used for overhead transmission lines with a nominal voltage no higher than 35 kV. 3. Definition of an Urban Area or Other Densely Built-up Area An urban area or other densely built-up area shall be defined according to the building-to-land _________________________________________________________________________________________________________________________________________ Page 82 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) ratio specified in Table 111-4. Where, the building-to-land ratio means the ratio of [the area covered with buildings / 50,000 m2 – the area of roads] in the zone (excluding roads) that is the rectangular area of 50,000 m2 extending for 50 m on both sides of an overhead transmission line and 500 m in the direction of that line. Table 111-4 An urban area or other densely built-up area New transmission conductor (when installed) The building-to-land ratio is no less than 25%. Existing transmission conductor The building-to-land ratio is no less than 30%. Article 112 Regulations for Side-by-side Installation and Adjacency to and Crossing with Other Objects When overhead transmission conductors are installed side by side, close to or across other objects, the transmission conductors shall be strengthened as follows: 1. Type 1 Transmission Line Strengthening Work Type 1 transmission line strengthening work shall be carried out as specified in the following items: (1) Strength of electrical conductors The strength of electrical conductors, excluding cables, shall be in accordance with Table 112-1. Nominal voltage No higher than 35 kV Higher than 35 kV but no higher than 130 kV Higher than 130 kV but no higher than 300 kV Higher than 300 kV (2) Table 112-1 Strength of electrical conductor Stranded wires with a tensile strength no less than 30 kN Stranded wires with a tensile strength no less than 40 kN Stranded wires with a tensile strength no less than 60 kN Stranded wires with a tensile strength no less than 80 kN Jointing of electrical conductors No jointing point shall be provided in the midway of a span excluding cases of compression joints. (3) Supporting structures Class B reinforced concrete poles, class B iron poles or steel towers shall be used as supporting structures. (4) Limitation of span The length of span of overhead transmission lines shall conform to Table 112-2. Table 112-2 Classification of supporting Strength of electrical conductor Length of span structures Stranded wires with a tensile strength no less than 30 No longer than 150 m Class B reinforced kN concrete poles or Stranded wires with a tensile strength no less than 40 class B iron poles As per Article 109-2 kN Stranded wires with a tensile strength no less than 60 Steel towers No longer than 400 m kN _________________________________________________________________________________________________________________________________________ Page 83 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Stranded wires with a tensile strength no less than 80 As per Article 109-2 kN (5) Shutoff time Electrical lines shall be equipped with devices that automatically shut off the electrical circuit within two seconds (or one second when the nominal voltage is higher than 35 kV) after an earth fault or short circuit occurs in the electrical circuit. 2. Type 2 Transmission Line Strengthening Work Type 2 transmission line strengthening work shall be carried out as specified in Table 112-3. Table 112-3 Classification of supporting structures Class A reinforced concrete poles or class A iron poles Class B reinforced concrete poles or class B iron poles Steel towers 3. Strength of electrical conductor Length of span Stranded wires with a tensile strength no less than 10 No longer than 100 m kN Stranded wires with a tensile strength no less than 10 kN Stranded wires with a tensile strength no less than 40 kN Stranded wires with a tensile strength no less than 10 kN Stranded wires with a tensile strength no less than 40 kN No longer than 200 m As per Article 109-2 No longer than 400 m As per Article 109-2 Type 3 Transmission Line Strengthening Work Type 3 transmission line strengthening work shall be carried out as specified in Table 112-4. Table 112-4 Classification of supporting structures Class A reinforced concrete poles or class A iron poles Class B reinforced concrete poles or class B iron poles Steel towers Strength of electrical conductor Stranded 10 kN Stranded 20 kN Stranded 10 kN Stranded 30 kN Stranded 40 kN Stranded 10 kN Stranded 30 kN Stranded 40 kN wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than wires with a tensile strength no less than Length of span No longer than 100 m No longer than 150 m No longer than 200 m No longer than 250 m As per Article 109-2 No longer than 400 m No longer than 600 m As per Article 109-2 3-5-6 Particulars of Installation for Side-by-side Use and _________________________________________________________________________________________________________________________________________ Page 84 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) at Adjacency to and Crossing with Other Objects 3-5-6-1 Article 113 1. Side-by-side Use Installation with Other Objects Installation with Distribution Conductors Side-by-side Installation of Overhead Transmission Conductors with a Nominal Voltage no higher than 35 kV and Overhead Distribution Conductors When overhead transmission conductors with a nominal voltage no higher than 35 kV and overhead distribution conductors are installed on the same supporting structure, the installation shall be carried out in accordance with the following requirements: (1) Position of installing electrical conductors on the supporting structure The electrical conductor with a higher voltage shall be installed above the electrical conductor with a lower voltage. When voltages are the same, overhead transmission conductors shall be installed above overhead distribution conductors using separate cross arms. This shall not apply where the electrical conductors with a higher voltage are cables and another electrical conductors are insulated conductors or cables. (2) Clearance The clearance between any overhead transmission conductor and any overhead distribution conductor shall be no shorter than the values specified in Table 113-1. (3) Strength of overhead distribution conductors Overhead distribution conductors shall be any of those specified in the following items except for cases where cables are used. a. b. Those with a tensile strength no less than 5 kN where the span of the overhead distribution conductor is no longer than 50 m Those with a tensile strength no less than 8 kN where the span of the overhead distribution conductor is longer than 50 m 2. Side-by-side Installation of Overhead Transmission Conductors with a Nominal Voltage Over 35 kV but Below 130 kV and Overhead Distribution Conductors (1) Overhead transmission conductors with a nominal voltage over 35 kV but below 130 kV and low-voltage overhead distribution conductors shall not be installed on the same supporting structure. (2) When overhead transmission conductors with a nominal voltage over 35 kV but below 130 kV and medium-voltage overhead distribution conductors are installed on the same supporting structure, the installation shall be carried out in accordance with the following requirements: a. Position of installing electrical conductors Overhead transmission conductors shall be installed above overhead distribution conductors using separate cross arms. This shall not apply where such overhead distribution conductor is installed together with overhead distribution conductor for the SWER system. b. Strength of overhead transmission conductors The overhead transmission conductors shall be the stranded wires with a tensile strength no less than 30 kN excluding the case where they are cables. _________________________________________________________________________________________________________________________________________ Page 85 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) c. Transmission line strengthening work Overhead transmission lines shall be installed according to the provisions for type 2 transmission line strengthening work. d. Clearance The clearance between any overhead transmission conductor and any overhead distribution conductor shall be no less than the values specified in Table 113-1. Nominal voltage No higher than 35 kV Higher than 35 kV e. Table 113-1 Clearance 2.0 m in case of a medium-voltage overhead distribution line and 1.2 m in case of a low-voltage overhead distribution line (0.5 m when the electrical conductor with a higher voltage is a cable and the other electrical conductor is an insulated conductor or a cable, and 1.0 m when the electrical conductor with a higher voltage is an insulated conductor and the other electrical conductor is an insulated conductor or a cable) Value obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to 2.0 m (or 1 m when the overhead transmission conductor is a cable and the overhead distribution conductor is an insulated conductor or a cable) Strength of overhead transmission conductor Overhead transmission conductors shall be installed according to Item (3) of Paragraph 1. 3. Side-by-side Installation of Overhead Transmission Conductors with a Nominal Voltage Over 130 kV and Overhead Distribution Conductors Overhead transmission conductors with a nominal voltage higher than 130 kV and overhead distribution conductors shall not be installed on the same supporting structure excluding the case of the following paragraph. 4. Side-by-side Installation of Overhead Transmission Conductors and Special Overhead Distribution Conductors Where any overhead transmission conductor or any overhead distribution conductor to be connected with any low-voltage electric machine or appliance to be installed on the supporting structure of the overhead transmission line is installed on the same supporting structure, the installation shall be carried out according to the provisions of Item (1) and Item (3) of Paragraph 1. Also, the clearance between the overhead transmission conductor and the overhead distribution conductor shall be no less than the values specified in Table 113-1. Article 114 1. Installation with Telecommunication Conductors Side-by-side Installation of Overhead Transmission Conductors with a Nominal Voltage No Higher Than 35 kV and Overhead Telecommunication Conductors When overhead transmission conductors with a nominal voltage no higher than 35 kV and overhead telecommunication conductors (excluding communication lines for power maintenance, the same applies hereafter in this article) are installed on the same supporting structure, the installation shall be carried out according to the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed according to the provisions for type 2 _________________________________________________________________________________________________________________________________________ Page 86 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) transmission line strengthening work. (2) Position of installing electrical conductors Overhead transmission conductors shall be installed above overhead telecommunication conductors using separate cross arms. (3) Strength and type of overhead transmission conductor Overhead transmission conductors shall be any of the following: (4) a. Stranded wires with a tensile strength no less than 30 kN b. Cable Types of telecommunication conductors Overhead telecommunication conductors shall be communications cables that have a metallic shielding layer. This shall not apply where overhead telecommunication lines are any of the following cases: (5) a. Where the overhead transmission conductor is a cable b. Where insulated conductors are used for overhead transmission conductors with the approval of the person responsible for the telecommunication line Clearance The clearance between any overhead transmission conductor and any overhead telecommunication conductor shall be no less than 2 m (or no less than 0.5 m when the overhead transmission conductor is a cable). (6) Vertical wiring of overhead transmission lines For vertical wiring of overhead transmission lines, cables shall be used for the portion from the point 2 m above the object installed on the supporting structure by the person who installs the telecommunication conductor to the lower end of the vertical wiring of the electrical lines. (7) 2. Earthing work a. An insulated conductor or a cable shall be used for the ground wire of an overhead transmission line. b. Any ground wire or ground electrode for overhead transmission lines shall be installed separately from any ground wire or ground electrode for overhead telecommunication lines. Side-by-side Installation of Overhead Transmission Conductors with a Nominal Voltage Over 35 kV and Overhead Telecommunication Conductors Overhead transmission conductors with a nominal voltage over 35 kV and overhead telecommunication conductors shall not be installed on the same supporting structure. Article 115 Low-voltage Appliances on Towers Where any low-voltage machine or appliance to be installed on the supporting structure of the overhead transmission lines is installed above overhead transmission conductors, it shall be installed in accordance with the following requirements: _________________________________________________________________________________________________________________________________________ Page 87 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) This shall not apply where the overhead transmission conductors are cables. (1) The electrical circuit to be connected to a low-voltage machine or appliance shall not be connected to any other loads. (2) Where the electrical circuit as specified in the preceding item is coupled with another electrical circuit through a transformer, an insulating transformer shall be used. (3) One terminal on the loaded side of the insulating transformer as specified in the preceding item or a neutral point shall be provided with class A earthing work. (4) Metal cases of low-voltage machines and appliances shall be provided with class D earthing work. 3-5-6-2 Article 116 1. Installations at Adjacency to and Crossing with Other Objects Adjacency to and Crossing with Buildings Primary Proximity of Transmission Conductors to Buildings Where overhead transmission conductors are installed in primary proximity to a building, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed according to the provisions specified for type 3 transmission line strengthening work. (2) Clearance a. The clearance between any overhead transmission conductor with a nominal voltage up to 35 kV and any building shall be no less than the values specified in Table 116-1. The clearance shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature sways in the wind. (The same shall apply hereafter in this article.) Table 116-1 Structural members of Type of transmission Clearance buildings conductor 2.5 m above the upper structural member, and 1.5 m below or on the side of the upper structural Insulated conductor member (or 1 m if installed so that there is no danger of any person contacting it easily) Upperstructural member 1.2 m above the upper structural member, and 0.5 (including TV antenna) m below or on the side of the upper structural Cable member Bare conductor Other members b. structural Insulated conductor Cable Bare conductor 3m 1.5 m (or 1 m if installed so that there is no danger of any person contacting it easily) 0.5 m 3m The clearance between any overhead transmission conductor with a nominal voltage over 35 _________________________________________________________________________________________________________________________________________ Page 88 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) kV and any structural member shall be no less than the values obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to the value specified in Table 116-1 depending on the classification of structural members of buildings and the type of electrical conductor. 2. Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage No Higher Than 35 kV to Buildings Where overhead transmission conductors with a nominal voltage no higher than 35 kV are installed in secondary proximity to buildings, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the provisions specified for type 2 transmission line strengthening work. (2) Clearance The clearance between overhead transmission conductors and buildings shall conform to Item (2) of Paragraph 1. 3. Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage Over 35 kV to Buildings Overhead transmission conductors with a nominal voltage over 35 kV shall not be installed in secondary proximity to buildings. 4. Close Clearance below Buildings Where an overhead transmission conductor is installed below and close to the building, it shall be installed in accordance with the following requirements: (1) Horizontal clearance The horizontal clearance between the overhead transmission conductor and the building shall be no less than 3 m (excluding insulated conductors with a voltage no higher than 35 kV or overhead transmission conductors using cables with a voltage below 130 kV). (2) Clearance The clearance between overhead transmission conductors and buildings shall conform to Item (2) of Paragraph 1. Article 117 1. Adjacency to and Crossing with Roads Primary Proximity of Overhead Transmission Conductors to Roads Where overhead transmission conductors are installed in primary proximity to roads or pedestrian crossing bridges (hereinafter referred to as "roads or the like"), they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the provisions specified for type 3 transmission line strengthening work. _________________________________________________________________________________________________________________________________________ Page 89 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (2) Clearance The clearance between any overhead transmission conductor and the road or the like (excluding the clearance on the surface of the road; The same shall apply hereafter in this article) shall be no less than the value specified in Table 117-1. The clearance shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature or sways in the wind. (The same shall apply hereafter in this article.) This shall not apply under any of the following conditions: a. Where the horizontal clearance between the overhead transmission conductors using insulated conductors with a nominal voltage no higher than 35 kV and the roads or the like is at least 1.5 m b. Where the horizontal clearance between the overhead transmission conductor, which uses a cable and has a nominal voltage no higher than 35 kV, and the road or the like is at least 1.2 m c. Where the horizontal clearance between the overhead transmission conductor, which uses a cable and has a nominal voltage over 35 kV but below 130 kV, and the road or the like is at least 2 m Table 117-1 Nominal voltage No higher than 35 kV Higher than 35 kV 2. (1) Clearance 3m The value obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to 3 m Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage No Higher Than 35 kV to Roads Where overhead transmission conductors with a nominal voltage no higher than 35 kV are installed in secondary proximity to roads or the like, they shall be installed in accordance with the following requirements: Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the provisions specified for type 2 transmission line strengthening work. (2) Clearance The clearance between overhead transmission conductors and roads or the like shall conform to Item (2) of Paragraph 1. 3. Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage Higher Than 35 kV to Roads Where overhead transmission conductors with a nominal voltage over 35 kV are installed in secondary proximity to roads or the like, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the strengthening work specified in Table 117-3. Closing distance of roads or the like Table 117-3 Strengthening work _________________________________________________________________________________________________________________________________________ Page 90 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) No longer than 100 m Over 100 m Type 2 transmission line strengthening work Type 1 transmission line strengthening work Where, "closing distance" means the following two items in cases where overhead transmission conductors are installed above or beside facilities such as roads, overhead telecommunication conductors or the like. (The same shall apply hereinafter in these Standards.) a. The length of a part of the facility installed in a horizontal distance less than 3 m continuously from the overhead transmission conductor b. The sum of the lengths of parts of the facility installed in a horizontal distance less than 3 m from the overhead transmission conductor in a span of the overhead transmission line (2) Clearance The clearance between overhead transmission conductors and roads or the like shall conform to Item (2) of Paragraph 1. 4. Crossing over Roads Where an overhead transmission conductor is installed crossing over a road or the like, the overhead transmission line shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the strengthening work specified in Table 117-4. Table 117-4 Closing distance of roads or the like Strengthening work No longer than 100 m Type 2 transmission line strengthening work Type 1 transmission line strengthening work (Note that type 2 transmission line strengthening Over 100 m work will do for overhead transmission lines with a nominal voltage no higher than 35 kV.) (2) Clearance The clearance between overhead transmission conductors and roads or the like shall conform to Item (2) of Paragraph 1. Article 118 1. Adjacency to and Crossing with Distribution Conductors and Telecommunication Conductors Primary Proximity of Overhead Transmission Conductors to Overhead Distribution Conductors or the like Where overhead transmission conductors are installed in primary proximity to overhead distribution conductors or overhead telecommunication conductors (hereinafter referred to as "overhead distribution conductors or the like"), they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the provisions specified for type 3 transmission line strengthening work. (2) Clearance The clearance shall be as specified below. The clearance shall be secured to provide for the _________________________________________________________________________________________________________________________________________ Page 91 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) occurrence of such case that the electrical conductor dips at the maximum design operating temperature or sways in the wind. (The same shall apply hereafter in this article.) a. The clearance between overhead transmission conductors with a nominal voltage no higher than 35 kV and overhead distribution conductors or the like or their supporting structures (including guys and pole braces) shall be no less than the values specified in Table 118-1. Table 118-1 Clearance (m) [Clearance: m] Classification of overhead transmission conductor Object Overhead distribution conductor Cable Insulated conductor Others 0.5 0.5 1 0.5 1 1 2 2 2 Cable Insulated conductor Others Overhead telecommunication conductor or supporting structure of overhead distribution conductor or the like 0.5 1 2 b. The clearance between overhead transmission conductors with a nominal voltage over 35 kV and overhead distribution conductors or the like or their supporting structures shall be no less than the values obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to 2 m (or 1 m when the overhead transmission conductors are cables). 2. Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage no higher than 35 kV to Overhead Distribution Conductors or the like Where overhead transmission conductors with a nominal voltage no higher than 35 kV are installed in secondary proximity to overhead distribution conductors or the like, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the provisions specified for type 2 transmission line strengthening work. (2) Clearance The clearance between overhead transmission conductors and overhead distribution conductors or the like or their supporting structures (including guys and pole braces) shall conform to Item (2) of Paragraph 1. (3) Horizontal clearance The horizontal clearance between overhead transmission conductors and overhead distribution conductors or the like shall be no less than 2 m when both electrical conductors are motionless. This shall not apply under any of the following conditions: a. Where the overhead distribution conductors or the like have a tensile strength no less than 10 kN or they are cables b. Where the overhead telecommunication conductors are installed with messenger wires using galvanized steel wires with a diameter no less than 4 mm or with a tensile strength no less than 4 kN, or when the overhead telecommunication conductors are service wires with spans no longer than 15 m _________________________________________________________________________________________________________________________________________ Page 92 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. c. Where the vertical clearance between the overhead transmission conductors and the overhead distribution conductors or the like is at least 6 m d. Where the overhead transmission conductors are insulated conductors or cables Secondary Proximity of Overhead Transmission Conductors with a Nominal Voltage Over 35 kV to Overhead Distribution Conductors or the like Where overhead transmission conductors with a nominal voltage over 35 kV are installed in secondary proximity to overhead distribution conductors or the like, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed in accordance with the strengthening work specified in Table 118-2. Table 118-2 Closing distance of overhead distribution Strengthening work conductors or the like No longer than 50 m Type 2 transmission line strengthening work Over 50 m Type 1 transmission line strengthening work (2) Clearance The clearance between overhead transmission conductors and overhead distribution conductors or the like or their supporting structures (including guys and pole braces) shall conform to Item (2) of Paragraph 1. (3) Horizontal clearance The horizontal clearance between overhead transmission conductors and overhead distribution conductors or the like shall be no less than 2 m. This shall not apply under any of the following conditions: a. Where the overhead distribution conductors or the like have a tensile strength no less than 10 kN or they are cables 4. b. Where the overhead telecommunication conductors are installed with messenger wires using galvanized steel wires with a diameter no less than 4 mm or with a tensile strength no less than 4 kN, or when the overhead telecommunication conductors are service wires with spans no longer than 15 m c. Where the vertical clearance between the overhead transmission conductors and the overhead distribution conductors or the like is at least 6 m d. Where the overhead transmission conductors with a normal voltage lower than 130 kV are insulated conductors or cables Crossing Over Overhead Distribution Conductors or the like Where an overhead transmission conductor is installed crossing over an overhead distribution conductor or the like and when it is installed above an overhead distribution conductor, the overhead transmission line shall be installed in accordance with the following requirements: (1) Transmission line strengthening work Overhead transmission lines shall be installed according to the strengthening work specified in _________________________________________________________________________________________________________________________________________ Page 93 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 118-3. Table 118-3 Closing distance of overhead Strengthening work distribution conductors or the like No longer than 50 m Type 2 transmission line strengthening work Type 1 transmission line strengthening work (Note that type 2 transmission line strengthening work will Over 50 m do for overhead transmission lines with a nominal voltage no higher than 35 kV.) (2) Clearance The clearance between overhead transmission conductors and overhead distribution conductors or the like or their supporting structures (including guys and pole braces) shall conform to Item (2) of Paragraph 1. (3) Others The overhead distribution conductor or the like (the uppermost one when there are two or more located vertically) shall has a tensile strength no less than 10 kN or it is a cable. 5. This shall not apply where overhead transmission conductors are insulated conductors with a nominal voltage no higher than 35 kV or cables with a nominal voltage below 130 kV. Adjacency to and Crossing Under Overhead Distribution Conductors or the like (1) Adjacency under overhead distribution conductors or the like Overhead transmission conductors shall not be installed below overhead distribution conductors or the like within a horizontal distance equivalent to the height of their supporting structures above the ground surface. (2) Crossing under overhead distribution conductors or the like Where overhead transmission conductors are installed across overhead distribution conductors or the like, the overhead transmission conductors shall not be lower than the overhead distribution conductors or the like. 6. Adjacency to and Crossing with Special Overhead Distribution Conductors Where overhead transmission conductors are installed close to or across the low-voltage overhead distribution conductors connected to low-voltage machines or appliances specified in Article 115, the overhead transmission conductors need not necessarily conform to the provisions of Paragraphs 1 through 4 (excluding the provisions for clearance). Article 119 1. Adjacency to and Crossing with Transmission Conductors Adjacency to and Crossing of Overhead Transmission conductors with other ones Where overhead transmission conductors are installed close to or across other overhead transmission conductors, they shall be installed in accordance with the following requirements: (1) Transmission line strengthening work The overhead transmission lines to be installed above or on the side shall be installed in accordance with type 3 transmission line strengthening work. (2) Clearance _________________________________________________________________________________________________________________________________________ Page 94 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The clearance shall be as specified below. The clearance shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature or sways in the wind. a. The clearance between an overhead transmission conductor and another overhead transmission conductor shall be no less than the values specified in Table 119-1 depending on the higher nominal voltage of the two transmission conductors. Table 119-1 Type of electrical conductor Clearance One overhead transmission conductor uses a cable and 0.5 m the other uses an insulated conductor or cable No higher than 35 kV Both overhead transmission conductors use insulated 1m conductors Others 2m The value obtained by adding 6 cm for Both overhead transmission every 10 kV and fraction thereof over 35 kV conductors use cables to 1 m Over 35 kV The value obtained by adding 6 cm for Others every 10 kV and fraction thereof over 35 kV to 2 m b. The clearance between an overhead transmission conductor and a supporting structure of another overhead transmission conductor shall be no less than the values specified in Table 119-2. Nominal voltage Nominal voltage No higher than 35 kV Over 35 kV 2. Table 119-2 Clearance 2 m (or 1 m when the electrical conductor is an insulated conductor and 0.5 m when it is a cable) The value obtained by adding 6 cm for every 10 kV and fraction there of over 35 kV to 2 m (or 1 m when the electrical conductor is a cable) Clearance between Overhead Transmission Conductors and Overhead Ground Wires Where overhead transmission conductors are installed close to or across overhead ground wires (including distribution conductors of SWER systems installed on the top of a steel tower) of other overhead transmission lines, the clearance between the overhead transmission conductors and the overhead ground wires shall be no less than the values specified in Table 119-2. Article 120 1. Adjacency to and Crossing with Other Facilities Primary Proximity Where overhead transmission conductors are installed in primary proximity to facilities other than buildings, roads, pedestrian crossing bridges, overhead telecommunication lines, overhead distribution lines and other overhead transmission lines (hereafter in this article, referred to as "other facilities"), they shall be installed in accordance with the following requirements: (1) Clearance The clearance shall be as specified below. The clearance shall be secured to provide for the occurrence of such case that the electrical conductor dips at the maximum design operating temperature or sways in the wind. _________________________________________________________________________________________________________________________________________ Page 95 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) a. The clearance between overhead transmission conductors with a nominal voltage no higher than 35 kV and other facilities shall conform to Table 120-1. Note that the clearance shall conform to Article 116 where overhead transmission conductors are installed above the buildings strong enough under which people can walk around freely. Table 120-1 Clearance Classification of other facilities above Upper structural member of below or on the building side Part of building other than upper structural members or facilities other than buildings b. (2) The electrical conductor is an insulated conductor 2 m or longer 1.2 m or longer 1 m or longer 0.5 m or longer 1 m or longer 0.5 m or longer The electrical conductor is a cable The electrical conductor is a bare conductor 2 m or longer 2 m or longer The clearance between overhead transmission conductors with a nominal voltage over 35 kV and other facilities shall be no less than the value obtained by adding 6 cm for every 10 kV and fraction thereof over 35 kV to 2 m (or 1 m when the overhead transmission conductors are cables and not installed above the upper structural members of building). Transmission line strengthening work The overhead transmission lines shall be installed in accordance with type 3 transmission line strengthening work. 2. Secondary Proximity or Crossing Where overhead transmission conductors are installed in secondary proximity to other facilities or they cross above other facilities, they shall be installed in accordance with the following requirements: (1) Clearance The clearance between overhead transmission conductors and other facilities shall conform to Item (1) of Paragraph 1. (2) Transmission line strengthening work The overhead transmission lines shall be installed in accordance with type 2 transmission line strengthening work. 3. Adjacency Under Others Where overhead transmission conductors are installed below and close to other facilities, the horizontal clearance between the two shall be no less than 3 m, and the clearance between them shall conform to Table 119-2. Note that the clearance between overhead transmission conductors and other facilities need not necessarily exceed 3 m when the overhead transmission conductors use insulated conductors and have a nominal voltage no higher than 35 kV or when they use cables and have a nominal voltage below 130 kV. 3-5-7 Protection against Lightning and Falling Trees _________________________________________________________________________________________________________________________________________ Page 96 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 121 Protection against Lightning The following measures shall be taken for overhead transmission lines to reduce flashover by lightning and protect facilities against damage caused by flashover. (1) Overhead ground wires shall be installed for the overhead transmission lines with a nominal voltage over 35 kV. Note that the distribution lines of SWER systems installed on the top of a tower can be regarded as overhead ground wires. (2) Arcing horns shall be installed for insulator devices of overhead transmission lines with a nominal voltage over 35 kV. (3) An armor rod shall be installed at the electrical conductor grasping part of suspension insulator devices. Article 122 Protection against Falling Trees Overhead transmission lines shall be installed in accordance with any of the following requirements to protect the facilities against damage caused by a falling tree. (1) Cut trees by the necessary length in an area where the facilities could be damaged by falling trees. (2) Secure the height of electrical conductors so as not to damage the facilities by falling trees. 3-5-8 3-5-8-1 Article 123 1. Underground Transmission Lines Dielectric Strength of Underground Transmission Lines Dielectric Strength of Underground Transmission Lines Dielectric Strength of Cables Cables used for underground transmission lines shall have the dielectric strength that withstands the power frequency voltage, the lightning impulse voltage and the switching surge voltage that are supposed on the cables. 2. Dielectric Strength of Underground Transmission Lines Underground transmission lines shall withstand the dielectric strength tests using the test methods specified in IEC 60840 or IEC 60502-2 "Electrical tests after installation" depending on the voltage. 3-5-8-2 Cables of Underground Transmission Lines _________________________________________________________________________________________________________________________________________ Page 97 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 124 1. Properties of Underground Cables Use of Cables Cables shall be used for underground transmission lines. 2. Electrical conductor Electrical conductors of cables shall have the electric resistance specified in IEC 60228 and shall be stranded wires composed of solid wires, such as annealed copper wire, annealed aluminum wire, hard-drawn aluminum wire and semi hard-drawn aluminum wire that satisfy the mechanical characteristics specified in Table 124-1. Table 124-1 Type of solid wire Annealed copper wire Annealed aluminum wire Hard-drawn aluminum wire Semi hard-drawn Diameter of solid wire No less than 0.10, no more than 0.28 More than 0.28, no more than 0.29 More than 0.29, no more than 0.45 More than 0.45, no more than 0.70 More than 0.70, no more than 1.6 More than 1.6, no more than 7.0 More than 7.0, no more than 16.0 No less than 2.0, no more than 5.2 More than 5.2, no more than 7.0 No less than 1.2, no more than 1.3 More than 1.3, no more than 1.5 More than 1.5, no more than 1.7 More than 1.7, no more than 2.1 More than 2.1, no more than 2.4 More than 2.4, no more than 2.7 More than 2.7, no more than 3.0 More than 3.0, no more than 3.5 More than 3.5, no more than 3.8 More than 3.8, no more than 4.1 More than 4.1, no more than 5.2 More than 5.2, no more than 6.6 No less than 1.2, no more than 1.3 Tensile strength (N/mm2) No less than 196, below (462 - 10.8d) No less than 59, below 98 No less than 159 No less than 186 No less than 186 No less than 182 No less than 176 No less than 169 No less than 166 No less than 162 No less than 162 No less than 159 No less than 159 No less than 155 No less than 98, below 159 Elongation (%) No less than 15.0 No less than 20.0 No less than 20.0 No less than 20.0 No less than 25.0 No less than 30.0 No less than 35.0 No less than 10.0 No less than 20.0 No less than 1.2 No less than 1.2 No less than 1.3 No less than 1.4 No less than 1.5 No less than 1.5 No less than 1.6 No less than 1.7 No less than 1.8 No less than 1.9 No less than 2.0 No less than 2.2 No less than 1.2 _________________________________________________________________________________________________________________________________________ Page 98 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) aluminum wire More than 1.3, no more than 1.5 More than 1.5, no more than 1.7 More than 1.7, no more than 2.1 More than 2.1, no more than 2.4 More than 2.4, no more than 2.7 More than 2.7, no more than 3.0 More than 3.0, no more than 3.5 More than 3.5, no more than 3.8 More than 3.8, no more than 4.1 More than 4.1, no more than 5.2 More than 5.2, no more than 6.6 No less than 98, below 186 No less than 98, below 186 No less than 98, below 183 No less than 98, below 176 No less than 98, below 169 No less than 98, below 166 No less than 98, below 162 No less than 98, below 162 No less than 98, below 159 No less than 98, below 159 No less than 98, below 155 No less than 1.2 No less than 1.3 No less than 1.4 No less than 1.5 No less than 1.5 No less than 1.6 No less than 1.7 No less than 1.8 No less than 1.9 No less than 2.0 No less than 2.2 d: diameter of solid wire (mm) 3. Insulator A cable shall have an insulator that is a butyl rubber compound, an ethylene propylene rubber compound or a polyethylene compound and have an electric shielding layer made of metal provided on the insulated conductor, or shall be a lead-covered cable, aluminum-covered cable or a cable with some other metal cover. Note that a cable used in an underwater transmission line specified in Article 135 may not necessarily have the electric shielding layer made of metal. 4. Shielding The shielding shall be of a tape shape with a thickness of 0.8 mm or thinner, a cover shape with a thickness of 2 mm or thinner, a braided form with a thickness of 2.5 mm or thinner, or a line shape with a diameter of 5 mm or less. Article 125 Jointing of Underground Cables Cables shall be jointed using a joint box that conforms to the following requirements: (1) (2) The joint box shall not increase the electric resistance of cables. The joint box shall have the dielectric strength equal to or higher than that of cables. (3) The joint box shall have a sufficient mechanical strength. (4) The joint box shall have a corrosion-free structure. Article 126 Earthing of Underground Cables and Joint Boxes Class D earthing work shall be provided on metallic members used for covering cables for underground transmission lines, metallic parts of joint boxes and metallic parts of protecting devices that house the cables (except for cable support hardware). This shall not apply to the parts where anticorrosion measures are taken. Article 127 Prevention of Over-voltage for Underground Cables If a cable of an underground transmission line could be damaged by over-voltage generated by a lightning impulse from an overhead transmission line or a high-frequency surge from a switching operation at a power plant or substation, the following countermeasures shall be taken severally or jointly. (1) Protecting an Insulator of a Cable a. Combination of earthing of a steel tower for overhead transmission lines with earthing of the termination joint box structure and the metallic sheath of the cable _________________________________________________________________________________________________________________________________________ Page 99 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. Installation of an arrester (2) Protecting an anti-corrosion layer a. Installation of parallel earthing wires b. Installation of a protecting device for the anti-corrosion layer 3-5-8-3 Article 128 1. Underground Installation of Cables Underground Installation of Cables Classification of Underground Installation A cable of an underground transmission line shall be installed in conduit systems, culvert systems or direct burial systems. 2. Installation Methods (1) Conduit systems and culvert systems Conduit and culvert systems shall be installed in accordance with the following requirements: a. These systems shall be rigid and durable and shall not affect other adjacent buried objects. b. Where these systems are buried under roads, they shall withstand the pressure from vehicles or other heavy objects and shall not affect the strength of the road. c. Buried depth shall be as follows: (a) (2) The buried depth under a road shall be over 0.8 m. (b) The buried depth under a sidewalk shall be over 0.6 m. Direct burial systems Direct burial systems shall be installed in accordance with the following requirements: a. To protect cables against shock, the direct burial systems shall be installed using any of the following methods: (a) Lay or nest underground transmission conductors in durable troughs and other protectors. (b) Use cables with durable insulating covers, such as copper bars and steel pipes, for underground transmission conductors and install them by covering the top and the side of the underground transmission cable with durable plates or conduits. b. Buried depth shall be as follows: (a) The buried depth shall be over 1.2 m in a place where there is a possibility of receiving pressure from vehicles or other heavy objects. (b) The buried depth shall be over 0.6 m in other places. Article 129 Indication of Buried Cables Where underground transmission lines are installed using a direct burial system or conduit _________________________________________________________________________________________________________________________________________ Page 100 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) system, they shall be marked in accordance with the following requirements: (1) The name of the line, the responsible person and the voltage shall be indicated. (2) Such indications shall be given noticeably with intervals of about 10 m. This shall not apply to restricted areas or places where the position of the electrical conductors can be recognized clearly. Article 130 1. Structures of Conduits, Culverts and Manholes Structure of a Conduit A conduit shall have the structure that conforms to the following requirements: (1) A conduit shall withstand the pressure of vehicles and other heavy objects. (2) A conduit shall be structured so that it is difficult for water to enter it. (3) A conduit shall have the inside diameter that allows cables to be drawn in and out smoothly and the inner surface shall be flat and smooth. (4) The radius of curvature of a curve on the conduit and the length of conduit between manholes shall be such that the tensile strength and the lateral pressure applied on cables when they are drawn in are less than the allowable limit. 2. Structure of a Culvert A culvert shall have the structure that conforms to the following requirements: (1) A culvert shall have the structure that can withstand the pressure of vehicles and other heavy objects. (2) A culvert shall be structured so that water can hardly enter into it. (3) A culvert shall have the form and dimensions that allow smooth installation and maintenance work of cables. The tolerable bending radius of cable shall be taken into consideration particularly at bends and branch points of the culvert. (4) If necessary, a drain, a ventilator, lighting, scaffolding for going up and down, a ladder and other facilities shall be installed. 3. Structure of a Manhole A manhole shall have the structure that conforms to the following requirements: (1) A manhole shall have the structure that can withstand the pressure of vehicles and other heavy objects. (2) A lid of a manhole shall be such that people other than operators cannot open it easily. (3) A manhole shall be structured so that it is difficult for water to enter it and water entering it can be removed. (4) Where a manhole has the size of 1 m3 or larger and there is a possibility that explosive or flammable gas may enter it, the manhole shall be equipped with a device to diffuse the gas. (5) A manhole shall be structured so that cables can be installed, maintained and keep functionality. _________________________________________________________________________________________________________________________________________ Page 101 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (6) If necessary, facilities for going up and down shall be installed in the gateway. (7) If there is a possibility that a manhole lid can be moved by a cable accident, a chain shall be installed on the lid. 3-5-8-4 Particulars of Prevention against Underground Electrical Inductive Interference Article 131 Protection of Underground Telecommunication Lines from Electrical Inductive Interference Underground transmission lines with a voltage over 35 kV shall be installed at a sufficient distance from underground telecommunications lines to avoid causing interference with communications through the underground telecommunication lines as a result of leak current or induction. 3-5-8-5 Article 132 1. Underground Installations at Adjacency to and Crossing with Other Objects Adjacency to and Crossing with Underground Telecommunication Lines Clearance and so on Where underground transmission conductors are installed close to or across underground telecommunication conductors, they shall be installed in accordance with the following requirements: (1) The clearance between the underground transmission conductors and the underground telecommunication conductors shall be no less than 60 cm. (2) When the clearance mentioned above is less than 60 cm, any of following countermeasures shall be carried out. a. Durable fireproof barriers shall be provided between the underground transmission conductors and the underground telecommunication conductors. b. The underground transmission conductors shall be nested in durable pipes that are nonflammable or are self-extinguishing and fireproof, and the pipes shall be installed in such a manner so as not to contact the underground telecommunication conductors directly. "Self-extinguishing" means materials that flame in fire and extinguish by themselves when fire is removed. "Fireproof" means the materials that flame in fire, but do not spread at least. "Nonflammable" means such materials as concrete, brick, tile, asbestos cement slate, steel, aluminum, glass, mortar and other materials that have incombustibility no less than that of these materials. (The same applies hereafter in this standard.) 2. Alternative Measures Paragraph 1 does not apply in any of the following cases: _________________________________________________________________________________________________________________________________________ Page 102 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (1) Where underground telecommunication conductors are communications lines for power maintenance and are optical fiber cables covered with materials that are nonflammable or are self-extinguishing and fireproof or optical fiber cables nested in pipes that are nonflammable or are self-extinguishing and fireproof; (2) Where underground telecommunication conductors are installed not to contact the communications lines for power maintenance directly; (3) Where underground telecommunication conductors are optical fiber cables covered with materials that are nonflammable or are self-extinguishing and fireproof or optical fiber cables nested in pipes that are nonflammable or are self-extinguishing and fireproof, and the responsible person has given the consent to the installation, or (3) Where underground transmission conductors have a nominal voltage below 130 kV and are installed with the approval of the person responsible for underground telecommunication conductors, and the clearance between the two is 10 cm or more. Article 133 Adjacency to and Crossing with Underground Distribution Lines Where underground transmission conductors are installed close to or across underground distribution conductors, the clearance between the two shall be no less than 30 cm. This shall not apply in any of the following cases: (1) Where each underground electrical conductor is: a. covered with materials that are self-extinguishing and fireproof, or b. nested in durable pipes that are self-extinguishing and fireproof. (2) Where either of those underground electrical conductors is covered with nonflammable materials (3) Where either of those underground electrical conductors is nested in durable pipes that are nonflammable (4) Where durable fire-resistant barriers are provided between those underground electrical conductors (5) Where those electrical conductors are installed close to or across each other in a manhole Article 134 1. Adjacency to and Crossing with Other Underground Objects Adjacency to and Crossing with Gas Pipes and Oil Pipes Where underground transmission conductors are installed close to or across pipes that contain flammable or toxic fluid and the clearance between the two is no more than 1 m, the underground transmission conductors shall be housed in durable pipes that are nonflammable or are self-extinguishing and fireproof, and such pipes shall be installed not to contact the pipes containing flammable or toxic fluid, excluding the case where durable fire-resistant barriers are provided between the underground electrical conductors and the pipes. 2. Adjacency to and Crossing with Water Pipes or the like Where underground transmission conductors are installed close to or across water pipes, steam pipes or the like and the clearance between the two is no more than 30 cm, the underground transmission conductors shall be housed in durable pipes that are nonflammable _________________________________________________________________________________________________________________________________________ Page 103 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) or are self-extinguishing and fireproof, excluding the case where durable fire-resistant barriers are provided between the underground electrical conductors and the pipes. This shall not apply to such cases where the water pipes, steam pipes or the like are nonflammable or are covered with nonflammable materials. 3-5-9 Special Transmission Lines Article 135 Underwater Transmission Lines Underwater transmission lines shall be installed in a place where they will not be damaged and so that they will not be exposed to risk, and shall conform to the following requirements: (1) Cables shall be used for the electrical conductors. (2) Cables shall be housed in durable pipes or cables armored with metal wires with a mechanical strength no less than that of galvanized steel wires with a diameter of 6 mm shall be used for underwater transmission lines. Article 136 Transmission Lines Over Bridges Transmission lines installed on the side or on the lower surface of bridges shall be installed in accordance with the following requirements: (1) Cables shall be used for the electrical conductors. (2) Cables shall be housed in durable pipes or troughs, or shall be installed so that nobody can touch the cables. (3) Class A earthing work shall be provided to the metallic parts of tubes and other protectors that contain cables, metallic electrical conductor joint boxes, and metallic members to be used for covering the cables (Class D earthing work be provided where they are installed so as for nobody to touch them), except where corrosion prevention measures are provided or the electric resistance to the ground is no more than 10. (4) Where electrical lines over bridges are installed close to or across other facilities, the clearance between them shall be no less than the values specified in Table 136-1. Table 136-1 Other facilities High, medium or low voltage circum-structural conductors, telecommunication conductors, water pipes and gas pipes Other facilities (excluding overhead and rooftop electrical conductors) Clearance 15 cm 30 cm _________________________________________________________________________________________________________________________________________ Page 104 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3-6 Distribution Lines 3-6-1 Common Rules for Distribution Lines Article 137 Allowable Voltages for Distribution Lines The power utility shall be attempted to maintain the voltage at power supply points to the value prescribed in IEC 60038 (1983-01) [IEC standard voltages] according to the nominal system voltage in conformity to Article 56-1-(1) and given in Table 137-1. Table 137-1 Nominal system voltage 230 volts 400 volts Article 138 Value to be maintained Value not exceeding 230 volts +6% or –10% Value not exceeding 400 volts +6% or –10% Insulation of Distribution Lines and User’s Sites 1. Principles of insulation (1) The live distribution line and electric circuit at users’ sites shall be insulated from the ground except for the points or places given in the following items: The connection point if the electric circuit is to be earthed (2) Places where it is very difficult to insulate a part of the circuit from the ground 2. Insulation levels of distribution lines and user’s sites (1) Insulation resistance of low-voltage wiring at users’ sites _________________________________________________________________________________________________________________________________________ Page 105 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The insulation resistance between conductors of low-voltage wiring and between the electrical circuit and ground shall be no less than the value given in Table 138-1 according to IEC 6034-1 (2005-10) [Electrical installations of buildings. Part 6: Verification. Chapter 61: Initial verification] with respect to the nominal circuit voltage for each section into which the electrical circuit can be divided by switching devices or over current circuit breakers. If insulation resistance measurement is difficult, it is sufficient to keep the leak current 1 mA or less. Table 138-1 Minimum of insulation resistance (Table 61A of IEC 60364-1) Nominal circuit voltage Test voltage d.c. [V] Insulation resistance [M] 250 ≧0.25 500 ≧0.5 SELV (no-earthing circuit) and functional special voltage: If the circuit is supplied with power from an insulating transformer (IEC 60364-411.1.2.1) and satisfies the requirements of IEC 60364-411.1.3.1 (electrically isolated from other circuits) 500 V or less (other than the above) Over 500 V 1,000 ≧1.0 Notes a: Insulation resistance measurement shall be conducted for each circuit with no equipment attached. b: If electronic equipment is present in the circuit, measurement shall be conducted only between a phase and the ground with the phase connected to the neutral conductor. (2) Insulation resistance of low-voltage distribution lines For the insulated section of a low-voltage distribution line, the insulation resistance between a wire and the ground and between conductors shall be such a value that the leak current for the operation voltage does not exceed 1/2000 of the maximum supply current. (3) Insulation level of medium-voltage distribution lines The insulation level of a medium-voltage distribution line shall be prescribed in terms of dielectric strength. However, if the insulation level is to be ascertained in terms of insulation resistance value as the need arises, it is sufficient to know that the electrical circuit subject to measurement is insulated from the ground. Article 139 1. Earthing of Distribution Lines and User’s Sites Classification of Earthing for Distribution Lines and User’s Sites The type of a distribution line and earthing at the user’s site shall be as described in the following items: For the various types of earthing, the places to be applied, installation conditions and the resistance to earth according to Article 57-2 or IEC 60364-3 (1993-03) [Electrical installations of buildings – Part 3: Assessment of general characteristics] (the same shall apply to such paragraphs mentioned below in this Article) shall be equal to or less than the value given in Table 139-1. (1) Power system earthing Power system earthing shall be executed at a transformer that connects a medium-voltage distribution line and a low-voltage distribution line to prevent an accident of the low-voltage distribution line, which may occur due to erroneous contact. For such earthing, Type B _________________________________________________________________________________________________________________________________________ Page 106 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) earthing work in Article 57-2 or TT or TN earthing of IEC60364-3 shall apply. The earthing electrode of Type B earthing work and the earthing electrode of Type C or Type D earthing work in Item (2) shall be mutually independent earthed systems (TT earthed system of IEC 60364-3). (2) Protective earthing If the insulation of electrical equipment deteriorates for some cause, an abnormal voltage may appear in the external exposed conductive parts (*1) from the internal live parts and there is a danger of electric shock. To hold down this excessive line-to-earth voltage, Type A earthing work shall be applied to medium-voltage distribution facilities, and Type C earthing work to low-voltage installations if the voltage exceeds 300 V and Type D earthing work or TT earthing of IEC60364-3 if the voltage is 300 V or less. (*1) “Exposed conductive parts” refers to parts such as steel stands, metal case or the like of apparatus installed in the electrical circuit. (3) Surge arrester earthing Earthing shall be applied to surge arresters to carry safely the lightning current that strikes the receiver to the ground. Earthing type System earthing Safety earthing Arrester earthing Table 139-1 Earthing types of distribution lines Application Installation conditions Resistance to earth () Value prescribed for Type B Distribution Low-voltage neutral conductor of TT earthing work or design transformer or TN earthing type value of TT or TN earthing Value prescribed for Type A For medium-voltage earthing work Value prescribed for Type C Exposed For low-voltage exceeding 300 V earthing work or design conductive value of TT earthing parts Value prescribed for Type D For low-voltage not exceeding 300 V earthing work or design value of TT earthing Surge For medium-voltage 20 arrester 2. Particularities of earthing of various types (1) Earthing arrangements and protective conductors The earthing electrode, earthing conductor and protecting earthing conductor shall conform to IEC 60364-5-54 (1980-01) [Electrical installations of buildings. Part 5: Selection and erection of electrical equipment. Chapter 54: Earthing arrangements and protective conductors] as to Properties, conductor diameter and diameter of conductor for equipotential bonding. The minimum diameter of protective earthing conductors shall conform to Table 139-2 according to the sectional area of the phase conductors of the facility. Table 139-2 Minimum sectional areas of protective conductors (Table 54F of IEC 60364-5-54-543.1.2) _________________________________________________________________________________________________________________________________________ Page 107 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Sectional area of phase conductor of facility S [mm2] S ≤ 16 16 < S≤ 35 S > 35 (2) Minimum cross-sectional area of protective conductor Sp [mm2] S 16 S/2 Installation of earthing conductor or earthing electrode The earthing conductor for earthing of the various types shall be installed as described below. a. The earthing conductor for earthing of the various types shall be of a corrosion-resistant metallic wire and shall be able to carry the current safely at failures. b. The earthing conductor shall be covered in the section from 40 cm underground to 2.5 m aboveground by a synthetic resin pipe or another shield of equivalent or higher insulating effect and strength. b. If the earthing conductor is installed along iron poles or other metallic objects, insulated conductor or cable shall be used for the full length of the earthing conductor. d. The earthing electrode of earthing of the various types shall be installed in depths not less than 45 cm underground. e. If the earthing conductor is installed along iron poles or other metallic objects, the earthing electrode shall be buried with a clearance of 2 m or more from those metallic objects. 3. Earthing of Steel Stands and Case of Equipment (1) The resistance to earth of steel stands and metal cases of equipment shall be at the resistance to earth in Table 139-2 or less according to the earthing types prescribed in Paragraph 1. (2) If the situation falls under any one of the following items, the resistance to earth may exceed the value given in Table 139-2 of Paragraph 1. a. If equipment to be used with its case in live condition is installed with a fence or the like to eliminate the danger of persons touching it. b. If low- or medium-voltage equipment is installed on a wooden pole to eliminate the danger of persons touching it. c. If the steel stand or case is fitted with an appropriate insulating base around. d. If the instrumental transformer without case is equipment covered with rubber, synthetic resin or other insulating substance. e. If a leakage circuit breaker (*2) is installed on the electrical circuit supplying electricity to low-voltage equipment installed at a place other than a moist place. (*2) This leakage circuit breaker is limited to the current-activated type with a rated sensible current of 15 mA or less and an activation time of 0.1 second or less. 4. Application of IEC 60364 (1) Low-voltage electrical equipment to be installed at user’s sites shall be installed according to IEC 60364-3. _________________________________________________________________________________________________________________________________________ Page 108 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) If directly connected to a power utility, the earthing method (TN or TT earthing) shall be the same as that of the power utility’s equipment involved in the supply of low-voltage electricity. (2) Low-voltage electrical equipment shall not be installed in such a manner of which earthing methods (TN and TT earthing) are different from those used at the same user’s site. Article 140 1. Equipment and Devices Installations for Distribution Lines Installation of Equipment and Devices for Medium-voltage Distribution Lines The equipment and devices that are installed on a medium-voltage distribution line (including the medium-voltage live conductor, except cables, attached to them; the same shall apply hereafter in this Article) shall be installed according to Article 69 and to meet either of the following items: (1) The equipment and devices shall be fitted with an appropriate fence around it to eliminate the danger of persons (*1) touching it. The height of the fence and the clearance from the fence to the live parts shall be 5 m or over, and a DANGER sign shall be posted. (*1) The term "persons" in this item means the public and excludes operators (the same shall apply hereinafter in this Article). (2) The equipment and devices shall be installed at a height of 5 m or more from the ground level and in such a manner that there is no danger of persons touching it. (3) The equipment and devices with its live parts not exposed shall be installed in such a manner that there is no danger of persons touching it easily. 2. Property of Oil-immersed Distribution Transformers Oil-immersed transformers for power distribution shall be installed according to IEC 60076-1 (1993-03) [Power transformers – Part 1: General], IEC 60076-2 (1993-04) [Power Transformers – Part 2: Temperature rise], IEC 60076-3 (2000-03) [Power transformers – Part 3: Insulation levels, dielectric tests and external clearances in air], IEC 60076-5 (2000-07) [Power transformers – Part 5: Ability to withstand short circuit] and their related IEC standards. 3. Property of Medium-voltage AC Load Switch The medium-voltage alternating-current load switch shall be installed according to IEC 62271-103 (2011-01) [High-voltage switches – Part 1: Switches for rated voltage above 1 kV and less than 52 kV], IEC 62271-1 (2007-05) [Common specifications for high-voltage switchgear and control gear standards] and related IEC standards. 4. Insulator Sets for Medium-voltage Distribution Lines (1) Mechanical strength of insulator sets The insulator set to support a medium-voltage distribution conductor shall be installed in such a manner that it will have a sufficient strength to attain a safety factor of 2.5 or over where calculated based upon the assumption that the following loads will act at the point of installation to the electrical conductor. a. For the insulator sets to anchor an electrical conductor, the load due to the assumed maximum tension of the electrical conductor b. For the insulator sets to support an electrical conductor, the horizontal lateral load or vertical load acting perpendicular to the axis of that insulator set _________________________________________________________________________________________________________________________________________ Page 109 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (2) Insulator set for urban area or Type 2 medium-voltage distribution line strengthening work If the medium-voltage distribution line is to undergo Type 2 medium-voltage distribution line strengthening work in conformity with Article 154-2 or to be installed in an urban area or other densely populated area in conformity with Article 154-3, the insulator set shall be as follows: However, the following shall not apply for Type 3 medium-voltage distribution line strengthening work. (3) a. An insulator set whose 50% impact flashover voltage value is 110% or more of the value of the insulator sets supporting other adjacent portions of that electrical conductor b. An insulator set with an arc horn attached to it and using suspension insulators, long rod insulators or line post (LP) insulators c. An insulator set using a series of two or more suspension insulators or long rod insulators d. An insulator set using two or more line post (LP) insulators Earthing of cross arms The cross arms to attach an insulator set supporting a medium-voltage distribution line shall be metallic and shall be earthed by earthing work Type D in Article 57-2. If pin insulators or line post insulators are to be directly attached to a wooden post as supports of an overhead distribution line, the relevant cross arms shall be earthed by earthing work Type D in Article 57-2. Article 141 Over current Breakers 1. Installation of Over current Breakers (1) On a medium-voltage distribution line, an overcurrent circuit breaker (*1) shall be installed on the primary side of a distribution transformer and at the out going point of a distribution substation. (*1) “Overcurrent circuit breaker” means a device to automatically break the circuit when an overcurrent occurs in the circuit. (2) In an indoor installation on a low-voltage distribution line and at a user’s site, it is desirable to install an over current circuit breaker at necessary places to protect the equipment and devices and electrical conductor. (*2) “An indoor installation on a low-voltage distribution line and at a user’s site” shall be hereinafter called a “low-voltage electrical circuit” in this Article. 2. Exceptions to Installation of an Over current Breaker No over current circuit breaker shall be installed at the following places: (1) Earthing conductor of earthing work (2) Neutral conductor of an electrical conductor. However, an over current circuit breaker may be installed if all the poles are shut off simultaneously. (3) The earthed conductor of a low-voltage overhead electrical conductor whose circuit is provided with Type B earthing in part. _________________________________________________________________________________________________________________________________________ Page 110 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. Properties of Overcurrent Breakers for Low-voltage Circuits (1) A fuse used on a low-voltage circuit as an over current circuit breaker shall conform to the following if installed horizontally. a. The fuse shall endure a current 1.1 times its rated current. b. The fuse shall melt in the prescribed time if a current 1.6 times or twice its rated current flows through it according to the rated current divisions shown in Table 141-1. Table 141-1 Melting time of fuses used in low-voltage electrical circuits Period Property of Rated Current When a current 1.6 times When a current 2 times the rated current flows the rated current flows Not exceeding 30 A 60 minutes 2 minutes Exceeding 30 A but not exceeding 60A 60 minutes 4 minutes Exceeding 60 A but not exceeding 100A 120 minutes 6 minutes Exceeding 100 A but not exceeding 120 minutes 8 minutes 200A Exceeding 200 A but not exceeding 180 minutes 10 minutes 400A Exceeding 400 A but not exceeding 240 minutes 12 minutes 600A Exceeding 600 A 240 minutes 20 minutes (2) A distributing circuit breaker used on a low-voltage electrical circuit as an over current breaker shall conform to the following: a. The distribution circuit breaker shall not automatically operate at a current 1.0 time the rated current. b. A distribution circuit breaker shall melt in the prescribed time if a current 1.25 times and twice the rated current flows through it according to the rated current divisions shown in Table 141-2. Table 141-2 Melting time of distribution circuit breakers used on low-voltage electrical circuits Period When a current 1.25 Property of Rated Current When a current 2 times times the rated current the rated current flows flows Not exceeding 30 A 60 minutes 2 minutes Exceeding 30 A but not exceeding 50A 60 minutes 4 minutes Exceeding 50 A but not exceeding 100A 120 minutes 6 minutes Exceeding 100 A but not exceeding 225A 120 minutes 8 minutes Exceeding 225 A but not exceeding 400A 120 minutes 10 minutes Exceeding 400 A but not exceeding 600A 120 minutes 12 minutes Exceeding 600 A but not exceeding 800A 120 minutes 14 minutes Exceeding 800 A but not exceeding 120 minutes 16 minutes 1,000A Exceeding 1,000 A but not exceeding 120 minutes 18 minutes 1,200A Exceeding 1,200 A but not exceeding 120 minutes 20 minutes 1,600A Exceeding 1,600 A but not exceeding 120 minutes 22 minutes _________________________________________________________________________________________________________________________________________ Page 111 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2,000A Exceeding 2,000 A c. 120 minutes 24 minutes A distribution circuit breaker need not conform to the provisions of b if it is installed according to IEC 60947-2 (1998-03) [Low-voltage switchgear and control gear – Part 2: Circuit-breakers]. (3) A circuit breaker on a low-voltage electrical circuit shall be capable of interrupting the short-circuit current passing through the place where it is installed. 4. Properties of Over current Breakers for Medium-voltage Electrical Circuits (1) A covered fuse used on a medium-voltage electrical circuit and installed as an over current circuit breaker shall endure a current 1.3 times the rated current and shall melt within 120 minutes at twice the rated current or conform to IEC 60282-1 (1998-01) [High-voltage fuses – Part 1: Current-limiting fuses]. (2) An open fuse used on a medium-voltage electrical circuit and installed as an over current circuit breaker shall endure a current 1.25 times the rated current and melt within 2 minutes at twice the rated current. (3) An over current circuit breaker operating when a short circuit occurs in the electrical circuit shall be capable of interrupting the short-circuit current passing through the place where it is installed. (4) An over current circuit breaker shall have a device to indicate its switching status according to its operation. However, if its switching status can be easily ascertained, it need not have such a device. Article 142 Earth Fault Breakers 1. Installation of Earth Fault Breaker for Low-voltage Electrical Circuits Exceeding 300 V On a low-voltage electrical circuit exceeding 300 V and coupled with a medium-voltage electrical circuit through a transformer, a device shall be installed to automatically break that low-voltage electrical circuit when an earth fault occurs in the electrical circuit. 2. Installation of Earth Fault Breaker for Low-voltage Electrical Circuit (1) On an electrical circuit to supply electricity to low-voltage equipment and devices enclosed with a metal case and installed at a place where there is the danger of persons easily touching it, a device shall be installed to automatically interrupt the circuit when an earth fault occurs in the electrical circuit. However, such a device need not be installed if the situation falls under one of the following: (2) a. If the equipment and devices are installed in a dry place. b. If the equipment and devices with a line-to-earth voltage of 150 V or less are installed in a place other than a moist place. c. If the resistance to earth of the earthing Type C or Type D provided on the devices is 3 or less. d. If the equipment and devices are covered with rubber, synthetic resin or other insulating material. If the equipment and devices named in Table 142-1 are installed at such places shown in the _________________________________________________________________________________________________________________________________________ Page 112 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) said Table, it is desirable to install a leakage circuit breaker. Table 142-1 Installed place of leakage circuit breaker Installed place of equipment and devices Equipment and devices used 3. Wet or moist place Washing machine, clothes dryer (in bathroom), hot water boiler, refrigerator-freezer (kitchen), laundry workshop, filling station’s car wash, and others Under the eaves (exposed to rain) Outdoor Well pump, air conditioner, washing machine, boiler, outdoor outlet, automatic vending machine, icebox, showcase, and others Outdoor unit of air conditioner, well pump, illuminating light around a pond, garden light, outlet installed outdoors, automatic vending machine, showcase, icebox, and others Used on a 400 V circuit (3-phase, 3-wire) Package, separate or window type air conditioner, large dry cleaning equipment, irrigation and drainage equipment, water supply, drainage, circulatory filtering equipment for swimming pools, and others Properties of Earth Fault Breakers The earth fault breaker shall be installed according to IEC 60947-2 (1998-03) [Low-voltage switchgear and control gear – Part 2: Circuit-breakers]. Article 143 1. Surge Arresters Places of Installation of Surge Arresters A surge arrester shall be installed in an electrical circuit of medium- and low-voltage distribution lines, at the places given in Article 80 and the following items, and places adjacent to these places. (1) On the medium-voltage side of a distribution transformer connected to an overhead distribution line. It is desirable to install a surge arrester at the following places as need arises to prevent distribution line accidents. (2) End of overhead distribution line (3) Installed place of switching devices (4) Near the installed place on the low-voltage side of a distribution transformer connected to an overhead distribution line (5) Connection point of overhead distribution conductor and cable (6) Installed place of voltage regulator, power capacitor or other similar equipment and devices (on both sides if it is series equipment) (7) If a distribution line is installed on top of steel towers, the primary support except the steel tower itself 2. Properties of Surge Arresters Properties of surge arresters installed on an electrical circuit of medium- and low-voltage distribution lines shall be as prescribed in the following items as well as IEC 60099-1 (1999-12) [Surge arresters – Part 1: Non-linear resistor type gapped surge arrester for a.c. Systems], IEC 60099-3 (1990-09) [Surge arresters – Part 3: Artificial pollution testing of surge arresters], IEC _________________________________________________________________________________________________________________________________________ Page 113 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 60099-4 (1998-08) [Surge arresters – Part 4: metal oxide surge arresters without gaps for a.c. systems], IEC 60099-5 (2000-03) [Surge arresters – Part 5: Selection and application recommendations] and related IEC standards. (1) Rated voltage of surge arrester For the rated voltage of a surge arrester, select the commercial frequency voltage value according to Article 80 as the reference voltage value to determine the characteristics of the surge arrester. (2) Nominal discharge current Nominal discharge current of a surge arrester is expressed as the wave height value of a lightning impulse current (waveform 8/20 s). Select it according to Article 80. For the surge arrester installed in an electrical circuit of medium- and low-voltage distribution lines, a value of 2.5 kA or more may be selected. (3) Reference voltage For the reference voltage of a surge arrester, a lower limit shall be selected according to the system voltage used. (4) Protective level The limiting voltage of a surge arrester shall be selected with an allowance of 20% or less for lightning impulses and 15% or less for switching impulses. 3-6-2 Overhead Distribution Lines 3-6-2-1 Article 144 1. Overhead Distribution Conductors Properties of Distribution Conductors Classification of Distribution Conductors The electrical conductors used in an overhead distribution line shall conform to the following items: The electrical conductors of low- and medium-voltage distribution lines are broadly classified into bare and insulated conductors. (1) Classification of bare distribution conductors Due care shall be taken when installing bare distribution conductors where there is a fear of the public suffering electric shocks, because the live parts thereof are exposed. The bare distribution conductors shall include hard-drawn copper wire, annealed copper wire, hard-drawn aluminum wire, aluminum alloy wire, aluminum-clad steel wire, steel-core aluminum stranded wire, and galvanized wire. (2) Classification of insulated distribution conductors The insulated distribution conductors shall be cross-linked polyethylene (XLPE) insulated conductor or polyvinyl chloride (PVC) insulated conductor according to the substance of the covering insulator. _________________________________________________________________________________________________________________________________________ Page 114 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2. Properties of Bare Distribution Conductors (1) Single conductors Single conductors shall have the conductivity and tensile strength (N) equal to the tensile strength per unit area (N/mm2) multiplied by its sectional area conforming to IEC 60028 (1925-01) [International standard of resistance for copper], IEC 60889 (1987-11) [Hard-drawn aluminium wire for overhead line conductors], IEC 60888 (1987-12) [Zinc-coated steel wires for stranded conductors], IEC 61232 (1993-06) [Aluminium-clad steel wires for electrical purposes] and related IEC standards, according to its metallic wire material. The tensile strength of hard-drawn copper wires shall be as shown in Table 144-1. Table 144-1 Tensile strength of hard-drawn copper wires Single conductor diameter (mm) Tensile strength (N/mm2) 0.4 or more and 12.0 or less (46.2 – 10.8d) or more d: Single conductor diameter (mm) (2) Twisted conductors Multiple single conductors stranded are called a twisted conductor, and twisted conductors include a simple twisted conductor made by stranding single conductors of the same kind and a compound twisted conductor made by stranding single conductors of two or more different kinds. Their tensile strength shall conform to Article 97. 3. Properties of Insulated Distribution Conductors (1) Properties of conductors The conductor shall be copper, aluminum or aluminum with a steel core and shall conform to Paragraph 2. (2) Properties of insulators a. Low- or medium-voltage XLPE insulators (a) Low-voltage XLPE insulators The low-voltage XLPE insulator thickness shall be equal to or more than the value prescribed in Table 144-2. Table 144-2 Low-voltage XLPE insulator thickness Conductor Low-voltage XLPE Insulator Twisted conductors Single conductors Thickness of the insulator (mm) (a nominal sectional area (mm2)) (diameter (mm)) 8 or more and 38 or less 2.0 or more and 3.2 or 2.5 less More than 38 and 150 or less 3.0 More than 150 and 325 or less 3.5 More than 325 and 500 or less 4.0 More than 500 and 600 or less 4.0 More than 600 and 1,600 or less 4.5 More than 1,600 and 2,000 or 5.5 less More than 2,000 6.0 _________________________________________________________________________________________________________________________________________ Page 115 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (b) Medium-voltage XLPE insulators The medium-voltage XLPE insulator thickness shall be equal to or more than the value prescribed in Table 144-3. Table 144-3 Medium-voltage XLPE insulator thickness Nominal sectional area of a conductor (mm2) 22 or more and 38 or less More than 38 and 150 or less More than 150 and 500 or less b. Thickness of an insulator (mm) 2.5 3.0 3.5 Low-voltage PVC insulators The low-voltage PVC insulator thickness shall be equal to or more than the value prescribed in Table 144-4. Table 144-4 Low-voltage PVC insulator thickness Conductor PVC Insulator Twisted conductors (a nominal Single conductors Thickness of an insulator sectional area (mm2)) (diameter (mm)) (mm) 0.75 or more and 3.5 or less 0.8 or more and 2.0 or less 0.8 More than 2.0 and 2.6 or 1.0 More than 3.5 and 5.5 or less less More than 2.6 and 3.2 or More than 5.5 and 8 or less 1.2 less More than 3.2 and 4.0 or 1.4 More than 8 and 14 or less less More than 4.0 and 5.0 or 1.6 More than 14 and 30 or less less More than 30 and 38 or less 1.8 More than 38 and 60 or less 1.8 More than 60 and 80 or less 2.0 More than 80 and 100 or less 2.0 More than 100 and 150 or less 2.2 More than 150 and 250 or less 2.4 More than 250 and 400 or less 2.6 More than 400 and 500 or less 2.8 More than 500 and 725 or less 3.0 More than 725 and 1,000 or less 3.2 More than 1,000 and 1400 or less 3.5 More than 1,400 and 2,000 or less 4.0 More than 2,000 4.5 (3) Dielectric strength and insulation resistance of the completed product The insulated conductor as a completed product shall undergo the test prescribed in Table 144-5 according to the type of the conductor and endure the dielectric strength and insulation resistance as indicated below. Table 144-5 Test of completed products Test method Type of insulated conductor Dielectric strength Test method Test voltage Insulation resistance Insulation Test method resistanc e value _________________________________________________________________________________________________________________________________________ Page 116 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Dielectric strength Test method Type of insulated conductor Medium-voltage XLPE (cross-linked polyethylene) insulated conductor PVC (polyvinyl chloride) insulated conductor or low-voltage XLPE Test method Test voltage Immerse in fresh water for one hour and then impress an alternating voltage between the conductor and earth for one minute. Alternating voltage of 25,000 V Alternating voltage of 3.500 V Insulation resistance Insulation Test method resistanc e value On completion of the dielectric strength test, impress a direct Value voltage of 100 V shown in between the Table conductor and earth 144-6 or for one minute and more then measure the insulation resistance. Table 144-6 Insulation resistance value Properties of insulators PVC Insulator XLPE Insulator Notes: R is the insulation resistance at 20 C. b. c. is the volume resistivity at 20 C (– cm). D is the outside diameter of the insulator (mm). d. d is the inside diameter of the insulator (mm). D D 1.8 , assume 1.8 for calculation. When d d Article 145 1. 51013 2.51015 a. e. Insulation resistance (Mkm) Volume resistivity (cm) R=3.66510-12 Load for an Overhead Distribution Lines and Safety Factor Classification and Minimum Strength of Overhead Distribution Conductors For medium- and low-voltage overhead distribution lines, conductors of the type and strength shown in Table 145-1 according to the operation voltage of the distribution line shall be used. Table 145-1 Operation voltage Distribution conductor type 300 V or less low-voltage More than 300 V The strength shall The strength shall be 7.0 be 5.0 kN or more kN or more in tensile in tensile strength. strength (10 kN or more in tensile strength if installed in an urban area). The strength shall The strength shall be 7.0 be 5.0 kN or more kN or more in tensile in tensile strength. strength (10 kN or more in tensile strength if installed in an urban area). Bare conductor Insul ated con duct or Type and strength of overhead distribution conductors XLPE insulator Medium-voltage The strength shall be 10.0 kN or more in tensile strength (30 kN or more in tensile strength if installed in an urban area). The strength shall be 10.0 kN or more in tensile strength (30 kN or more in tensile strength if installed in an urban area). PVC insulator (*1) Cable There are no regulations on the thickness of the cable itself because cables in installed condition are suspended from a messenger wire. _________________________________________________________________________________________________________________________________________ Page 117 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (*1) 2. PVC insulator, which exceeded 300V, can be used when the facilities of other insulated conductors are difficult. Safety Factors for Overhead Distribution Conductors The medium- and low-voltage overhead electrical conductors shall be installed so that the safety factor for tensile strength of the conductor is 2.5 or more when the assumed load given in Table 145-2 is impressed, except for Paragraph 3. Table 145-2 Assumed load on overhead distribution conductors Load direction Vertical Horizontal A horizontal wind pressure of 790 N per 1 m2 of vertically projected area Conductor weight of an electrical conductor conforming to Article 150 (Table 150-1) 3. Installation by means of overhead cable (1) Installation by means of low-voltage overhead cable The low-voltage overhead distribution line shall be installed as follows if cable is to be used for the electrical conductor. a. The cable shall be installed according to one of the following: (2) (a) Install the cable with hangers suspended from a metallic wire to suspend the cable (*2). (b) Keep the cable in contact with a messenger wire and wind a corrosion-resistant metallic tape or the like over them in spiral form at intervals of 20 cm or less. (c) (*2) Install the cable by attaching a messenger wire firmly to the cable armor. The “metallic wire to suspend a cable” is hereafter called a “messenger wire.” b. The messenger wire shall be a twisted conductor with a tensile strength of 7.0 kN or more or a galvanized stranded iron wire with a sectional area of 22 mm2 or more. b. The messenger wire shall be installed with the safety factor according to Paragraph 2. d. Earthing work Type D in Article 57-2 shall be applied to the metals used for the messenger wire and cable covering. However, earthing work Type D in Article 57-2 is not necessarily applicable to the messenger wire if an insulated electrical conductor or another conductor having equivalent or higher insulating effect is used for the messenger wire. Installation by means of medium-voltage overhead cable The medium-voltage overhead distribution line shall be installed as follows if cable is to be used for the electrical conductor. a. The cable shall be installed according to one of the following: (a) Install by means of hangers for a messenger wire. In this case, the hanger intervals shall be 50 cm or less. (b) Keep the cable in contact with a messenger wire and wind a corrosion-resistant metallic tape or the like over them in spiral form at intervals of 20 cm or less. (c) Install the cable by attaching a messenger wire firmly to the cable armor. _________________________________________________________________________________________________________________________________________ Page 118 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. The messenger wire shall be a twisted conductor with a tensile strength of 15 kN or more or a galvanized stranded steel wire with a sectional area of 22 mm2 or more. c. The messenger wire shall be installed with the safety factor according to Paragraph 2. d. Earthing work Type D in Article 57-2 shall be applied to the metals used for the messenger wire and cable covering. Article 146 Jointing of Overhead Distribution Conductors 1. Splicing of overhead distribution conductors (1) Electric resistance at splice In any case of electrical conductor splicing, the electric resistance of the electrical conductors shall not be increased at the splice. (2) Mechanical strength of splice When splicing bare conductors, or a bare conductor and insulated conductor or cable, or insulated conductors, or an insulated conductor and cable, the mechanical strength of the electrical conductors shall not be decreased 5% or more at the splice. However, this excludes jumpers and other portions where no or little tension acts on the splice. (3) Splicing method For the splicing given in Item (2), the splice shall be made using a splicing sleeve or another device or by brazing. However, this excludes portions where brazing work is difficult for technical reasons. (4) Insulating effect at splice When splicing insulated conductors, or an insulated conductor and a cord or cable, the splice shall be sufficiently covered with an insulating material having an insulating power equal to or more than the insulated conductor or a splicing device having equal or larger insulating effect shall be used. (5) Splicing of cords, cables, or a cord and cable When splicing cords to each other, or cables to each other, or a cord and a cable, a cord connector, connection box or other device shall be used. Direct connection is prohibited. However, direct connection is allowed for cables without a metallic sheath according to the prescriptions of Items (1) to (4). (6) Splicing of aluminum and other wires When connecting conductors of different electrochemical properties, electrical corrosion shall not occur at the splice. If insulated conductor or cable using aluminum for the conductors is used for indoor, eaves and outdoor wiring, a connector shall be used when connecting the electrical conductor concerned. 2. Branching of overhead distribution conductor Branching of an overhead distribution conductor shall take place at a support of that electrical conductor except the case where installed according to Article 145-3 or installed so that no tension is exerted on the electrical conductor at the branch. _________________________________________________________________________________________________________________________________________ Page 119 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 147 1. Dielectric Strength of Overhead Distribution Lines Dielectric Strength of Medium-voltage Distribution Lines The dielectric strength of the electrical circuits on a medium-voltage distribution line shall be such that the circuit endures the test voltage when tested with a voltage 1.25 or more times (*1) the maximum operation voltage impressed between the circuit and earth for 10 minutes (*2). 2. (*1) 1.5 times the maximum operation voltage for distribution lines with a maximum operation voltage of 7,000 V or less. If a cable is used for the electrical conductor, a direct voltage twice the alternating test voltage may be used. (*2) If it is difficult to carry out a testing for 10 minutes for technical reasons, 5 or more minutes test may be made. Dielectric Strength of Distribution Equipment and Devices The dielectric strength of the transformers, rectifiers, switching devices and other distribution equipment and devices installed on a distribution line shall be such that the equipment endures the test voltage when the test voltage shown in Table 147-1 is impressed at the point of impression for 10 minutes continuously (*3). For the AC connection point or bus bar of distribution equipment and devices using a cable for the electrical conductor, the test voltage may be twice the direct voltage. For the transformers, rectifiers, switching devices and other distribution equipment and devices that have undergone the withstand voltage test at the factory according to IEC 60071-1 (1993-11) [Insulation co-ordination – Part 1: Definitions, principles and rules] and related IEC standards, the normal line-to-earth voltage value according to Article 56 may be used. (*3) If it is difficult to carry out a testing for 10 minutes for technical reasons, 5 or more minutes test may be made. Table 147-1 Dielectric strength of distribution equipment and devices Type of distribution equipment and devices Transformer (*4) Medium-voltage winding with the highest voltage exceeding 7,000 V Medium and low-voltage winding with the highest voltage of 7,000 V or less Rectifier (excluding the mercury type) Distribution equipment and devices other than the above (*5) Medium-voltage distribution equipment and devices with the highest voltage exceeding 7,000 V Mediumand low-voltage distribution equipment and devices with the highest voltage of 7,000 V or less Point of application of test voltage Between the winding under test and another winding and between core and case Between live parts and case Test voltage Voltage 1.25 times the highest voltage Voltage 1.5 times the highest voltage (at least 500 V) Alternating voltage once (equal to) the highest voltage on the direct-current side (at least 500 V) Voltage 1.25 times the highest voltage Between live parts and earth Voltage 1.5 times the highest voltage (direct voltage 1.5 times or alternating voltage once (equal to) the maximum operation voltage for the direct-current live parts) (500 V if that voltage is less than 500 V) _________________________________________________________________________________________________________________________________________ Page 120 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (*4) The term “transformer” excludes the instrumental transformer, test transformer, discharge lamp transformer and other special-purpose types. (*5) “Distribution equipment and devices other than the above” includes the switching device, circuit breaker, power capacitor, instrumental transformer and other distribution equipment and devices. However, the surge arrester is excluded. Article 148 1. Guard lines, Guard Nets and Protection Devices Division of application The division of application of guard lines, guard nets and protective devices shall conform to the following items: (1) In case of approaching or intersecting a high-voltage overhead transmission line: a. A guard net shall be installed if the medium- or low-voltage overhead distribution line approaches a high-voltage overhead transmission line from below with a clearance of less than 3 m. However, the guard net may be omitted if the high-voltage overhead transmission conductors are installed by Type 2 transmission line strengthening work according to Article 112. b. A guard line or guard net shall be installed if the medium- or low-voltage overhead distribution conductor intersects under a high-voltage overhead transmission conductor. However, such a device may be omitted if the high-voltage transmission conductor is installed by Type 2 transmission line strengthening work according to Article 112 and conforms to one of the following: (a) If the top conductor of the overhead distribution conductor has a tensile strength of 10 kN or over. (b) If the overhead distribution conductor is a cable. (c) If the vertical clearance from the high-voltage overhead transmission conductor to the overhead distribution conductor is 6 m or more . (2) In case of crossing an overhead telecommunication conductor If the medium-voltage overhead distribution conductor intersects an overhead telecommunication conductor, it may be installed only if a robust protective device is installed above the medium-voltage overhead distribution conductor. (3) In case of crossing another low-voltage overhead distribution conductor If the medium-voltage overhead distribution conductor intersects under a low-voltage overhead distribution conductor, it may be installed only if a robust protective device is installed above the medium-voltage overhead distribution conductor. (4) If the overhead distribution conductor adjacencies or crossings a cableway: If the overhead distribution conductor adjacencies or crossings under a cableway (*1) with a clearance of less than 3 m, it may be installed only if a robust protective device is installed above the overhead distribution line. However, such a device may be omitted if it conforms to one of the following: a. If the horizontal clearance to the cableway is 3 m or more b. If the horizontal clearance to the cable way is 2 m or more for low-voltage overhead _________________________________________________________________________________________________________________________________________ Page 121 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) distribution conductors and 2.5 m or more for medium-voltage overhead distribution conductors and there is no danger of the cableway’s contacting the overhead electrical conductor even when pole braces of the cableway collapse (*1) The term cableway includes the carriages but excludes the cableway pole braces 2. Structures of guard lines, guard nets and protective devices (1) Guard lines and guard nets The guard line shall be a firmly supported metallic wire of two or more strands, and the guardnet shall be a metallic net. Their structure shall conform to Table 148-1. Table 148-1 Structure of guard line and guard net Division of application Guard net Item Guard line Tensile strength 10 kN or over Warp intervals 1.5 m or less Woof Tensile strength 7.0 kN or over Woof intervals 1.5 m or less Overhand width beyond the overhead 1/2 or more of the vertical clearance to the overhead electrical conductor electrical conductor (30 cm if this clearance is less than 30 cm) Clearance to the overhead electrical 60 cm conductor Earthing Earthing work Type A Earthing work Type D Warp (2) Protective devices The protective device shall be a firmly installed protective device and its metallic parts shall be earthed by earthing work Type D according to Article 57-2. 3-6-2-2 Article 149 Supporting Structures of Distribution Lines Supporting Structures of Distribution Lines 1. Installation of Supporting Structures (1) The supporting structures of an overhead distribution line shall not be installed to go through the space between electrical conductors of another overhead distribution line or overhead telecommunication line. (2) The overhead distribution conductors shall not be installed with a supporting structure of another overhead distribution line or overhead telecommunication line in between. (3) If the overhead distribution conductor are installed together with another overhead distribution conductor or overhead telecommunication conductor on the same supporting structure, the provisions of Items (1) and (2) above shall not apply to such installation. 2. Limitation of Span of Supporting Structures The span of supporting structures shall be the value in Table 149-1 or less according to the type of the supporting structure. Type 2 and Type 3 medium-voltage distribution line strengthening work are prescribed in Article 154-2 and installation in urban areas in Article 154-3. Table 149-1 Maximum span of supporting structures Classification of Low Medium voltage _________________________________________________________________________________________________________________________________________ Page 122 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) supporting structures voltage Ordinary Wooden pole, class A iron pole, or class A reinforced concrete pole Class B iron pole or class B reinforced concrete pole 150m 150 m Type 2 distribution line strengthening work 10 kN or over; 100 m 10 kN or over; 200 m 250m 250m 40 kN or over; 500 m 600m 20 kN or over; 150 m 600m 75m 150m 40 kN or over; No limitation 10 kN or over; 400 m 30 kN or over; 600 m 40 kN or over; Long-span work (*3) Urban area (*1) 10 kN or over; 200 m 30 kN or over; 250 m 10 kN or over; 400 m Steel tower Type 3 distribution line strengthening work 10 kN or over; 100 m 400m (250m) (*2) 40kN or over; Longspan work (*3) (*1) Iron poles, reinforced concrete poles or steel towers shall be used for the supporting structure of an overhead distribution line installed in an urban area. (*2) If the intervals of electrical conductor in horizontal arrangement are less than 4 m (*3) Steel towers of the tension-proof type shall be used for the steel towers of long-span work according to Article 109-2-(2). 3. Clearance between medium-voltage overhead electrical conductors and supporting structures (1) The clearance between the medium-voltage overhead electrical conductor and its supporting structures, cross arms, pole braces, and guys shall be the value in Table 149-2 or more. With arc horn (*4) Without arc horn Table 149-2 Clearance to supporting structures and the like 15 kV or over but less than 25 25 kV or over but less than 35 kV kV 1.2 times the arc horn gap 1.2 times the arc horn gap (minimum 20 cm) (minimum 25 cm) 35cm 45cm (*4) “With arc horn” is limited to the type that can restrict the arc direction. (2) The clearance between electrical conductors of the same circuit of a medium-voltage overhead conductor shall be the value in Table 149-3 or over. However, this provision shall not apply to the distribution line using a spacer wire and so on. Table 149-3 Clearance of the same circuit Voltage division Wire interval 15 kV or over but less than 25 kV 35cm 25 kV or over but less than 35 kV 45cm Article 150 1. Load for Supporting Structures of Distribution Lines and Safety Factor Wind Load The values in Table 150-1 shall be used for wind load according to the type of the supporting structure. If the wind load is calculated from wind pressure (wind tunnel) experiments based on a wind speed of 35 m/s, that load value may be used. _________________________________________________________________________________________________________________________________________ Page 123 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 150-1 Wind load Segment of an object receiving wind pressure Wooden pole Columnar pole Triangle or rhombic pole Square pole consisting of steel pipes Iron pole Wind pressure to 1 m2 of the vertical projected area of the structural material 630 N 630 N 1,500 N Others Supporting structure Columnar pole Others Single pole Columnar pole (excluding Hexagonal or cross arms) octagonal pole Iron tower Those consisting of steel pipes (excluding single poles) Others Conductors forming multiple conductors (Limited to those in which two compositional distribution conductors are arranged Distribution horizontally and the clearance between such distribution conductors is no more than twenty conductor times their outer diameter, the same applies hereafter) Others Insulator device for medium-voltage distribution line Cross arm for a wooden pole, an iron pole limited to a columnar pole, and a reinforced concrete pole for medium-voltage distribution line 2. Iron-reinforced concrete pole 1,180 N 1,740 N if the webs overlap in front and behind, and 1,890 N for other cases 630 N 950 N 630 N 1,180 N 1,350 N 2,290 N 710 N 790 N 1,100 N 1,260 N if used as a single object, and 1,740 N for other cases Strength of Supporting Structures and Safety Factor The supporting structures of medium- and low-voltage overhead distribution lines shall have the prescribed strength and safety factor to the load shown in Table 150-2. Table 150-2 Strength and safety factor of supporting structures of medium- and low-voltage overhead distribution lines Load & Safety Factor Supporting Structure Load to withstand Low voltage Medium voltage Strength of supporting structures to the load given to the left Low-voltage Medium-voltage Ordinary: Safety factor 1.5 or over. Wooden pole Wind load (1) Wind load (2) Vertical load a. Pole Type A Iron pole Wind load b. Weight of distribution conductors and supporting structures Vertical component of tension in Safety factor 1.2 or over Type 2 distribution line strengthening work: Safety factor 2.0 or over A safety factor of 1.5 or over to the assumed normal load shall be secured by the yield-point strength of the structural members according to Article 103. However, conformance with Article 103 is not mandatory if the pole is a steel tube pole and the complete pole can endure the load when 3 times the design load is exerted perpendicular to the pole axis at the point 30 cm from the top with the pole fixed from the pole bottom to 1/6 of the entire length of the pole (*1) so that no deformation occurs in the pole. _________________________________________________________________________________________________________________________________________ Page 124 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Composite pole (reinforced concrete pole in combination with steel pipe) distribution conductor and guy Others Rein-forced concrete pole Wind load Pole Type B Iron tower Reinforced concrete pole Iron tower 3. (1) Wind load (2) Vertical load; Same as (2) above (3) Horizontal component of tension in distribution conductor The complete pole shall endure the load when twice the design load is exerted perpendicular to the pole axis at the point of 30 cm from the top with the pole fixed from the pole bottom to 1/6 of the entire length of the pole (*1) so that no deformation occurs in the pole. A safety factor of 1.5 or over to the assumed normal load shall be secured by the yield-point strength of the structural members according to Article 103. However, conformance with Article 103 is not mandatory if the pole is a precast reinforced concrete pole and the complete pole can endure the load when twice the design load is exerted perpendicular to the pole axis at the point 30 cm from the top with the pole fixed from the bottom to 1/6 of the entire length of the pole (*1) so that no deformation occurs in the pole. Same as pole Type A A safety factor of 1.5 or over to the assumed normal load and a safety factor of 1.0 or over (*2) to the assumed abnormal load shall be secured by the yield-point strength of the structural members according to Article 103. (*1) This length shall be 2.5 m if “the length from the pole bottom to 1/6 of the entire length of the pole” exceeds 2.5 m. (*2) The safety factor shall be 1.5 or over for the cross arms. Calculation of Strength of Wooden Poles If wooden poles are used for the supporting structure of an overhead distribution line, the strength calculation for the wind load perpendicular to the overhead distribution line shall take place using the following equation: (1) For the low-voltage overhead distribution line a. Single pole without guy 390D 0 H 2 234H 3 S 98dh P K 3 F 10 D 0 S: is the sum of the halves of the spans on both sides (m). D: is the outer diameter of the distribution conductor (mm). H: is the height of the supporting structure of the distribution conductor from the ground surface (m) H: is the height of the wooden pole from the ground surface (m). D0: is the diameter of the wooden pole at the ground surface (m) calculated by the following formula. _________________________________________________________________________________________________________________________________________ Page 125 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) D0 = D + 0.9H D: is the top end diameter of the wooden pole (m). D0’ is the diameter of the circle (cm) of equal area to the sectional area of the wooden pole at the ground surface from which the area of the decayed parts is subtracted if the wooden pole is decayed at the ground surface. P: is the breaking strength of the wooden pole against bending according to the type of wooden poles given in Table 150-3. F: is the safety factor for the wooden pole. K: is a coefficient depending on wind load taking a value of unity. Table 150-3 Breaking strength Classification of wooden poles Breaking strength Cedar 39 N/mm2 Cypress and chestnut trees 44 N/mm2 White fir and spruce 42 N/mm2 Oregon pine 55 N/mm2 Others The values equivalent to those listed above b. Single pole with guy 195D 0 H 2 117H 3 0.5S 98dh P K 3 F 10 D 0 S, d, h, H, D0, D0’, P, F and K are the same as those defined in a. c. H-pole without guy 390D 0 H 2 234H 3 0.5S 98dh P K 3 F 10 D 0 S, d, h, H, D0, D0’, P, F and K are the same as those defined in a. d. H-pole with guy 195D 0 H 2 117H 3 0.25S 98dh P K 3 F 10 D 0 S, d, h, H, D0, D0’, P, F and K are the same as those defined in a. (2) For the medium-voltage overhead distribution line The prescriptions in Item (1) apply accordingly. insulator sets and cross arms shall be added. (3) In this case, the wind load acting on the Guy in Items (1) and (2) _________________________________________________________________________________________________________________________________________ Page 126 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) a. Guy used with single poles anp K 12.5S 98dh 4875D 0 H 2 2925H 3 cosec 3 h 0 10 a: n: P: h0: : is the coefficient of tensile load reduction of the twisted conductor. is the necessary number of strands if the safety factor of the guy is 2.5. is the tensile strength (N) of one strand. is the height of the guy-attaching point from the ground surface (m). is the angle between the guy and pole. S, d, h, H, D0 and K are the same as those defined in Item (1)-a. b. Guy used with H-poles anp K 12.5S 98dh 9750D 0 H 2 5850H 3 cosec 3 h 0 10 a, n, p, h0 and are the same as those defined in a. and S, d, h’, H, D0 and K are the same as those defined in Item (1)-a. 4. (1) Calculation of Strength of Reinforced Concrete Poles and Iron Poles Calculation of strength against wind load perpendicular to the distribution line Calculation of the strength of reinforced concrete poles and iron poles used as the supporting structure of a distribution line against wind load perpendicular to the distribution line shall take place as follows: ( H 0.25) P (2 D1 D 0) H 2 K1 K 2 S ( dh) f 6 (2) P: is the breaking load of the supporting structure (standard design load 2) (N). K1: is the wind load (N) per 1 m2 of vertically projected area of the supporting structure. K2: is the wind load (N) per 1 m2 of vertically projected area of the distribution conductors. D1: is the top end diameter (m) of the supporting structure. D0 : is the ground-level diameter (cm) of the supporting structure. H: is the height of the supporting structure above the ground (m). S: is a half of the sum of the spans on the both sides (m). d: is the diameter of the distribution conductor (mm). h: is the height of the supporting structure of the distribution conductor from the ground surface (m). f: is the safety factor of the supporting structure. Calculation of strength against vertical load and bending moment Calculation of the strength of iron poles and reinforced concrete poles used as the supporting structure of a distribution line against vertical load and bending moment shall take place as _________________________________________________________________________________________________________________________________________ Page 127 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) follows: W M A Z where : is the allowable bending moment (N/cm2) of the structural material of the supporting structure. W: is the vertical load (N) present above the cross section in which strength calculation takes place. M: is the bending moment (Ncm) due to the load present above the cross section in which strength calculation takes place. A: is the equivalent sectional area (cm2). Calculation method of A For 0 2 mE A2 P A1 A1 P P A2 2 2 A A2 1 2 A2 mE y A1 mE A2 P A1 1 mE A A2 2 For 2 y 2 0.4133 I1 0.0001 0.01 I2 I1 ｍ＝0.0804 10 4 I 2 I1 0.01 0.4 I2 I1 ｍ＝0.114 10 4 I 2 I1 0.4 1.0 I2 I1 ｍ＝1.472 0.995 I2 2: 0.3373 is the slenderness ratio of the pole [(length (cm) of the pole from the point of load action to the ground level)/(radius (cm) of gyration of area of the pole at the ground level)] E: y : is Young’s modulus (N/cm2) is the yield point (N/cm2) p : is the elastic limit (0.8y) I1 and I2 : are the moments of inertia (cm4) of the pole at the point of load application and at the ground level. A1 and A2 : are the sectional areas (cm2) of the pole at the point of load the ground level. application and at _________________________________________________________________________________________________________________________________________ Page 128 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Z: 5. is the modulus of section (cm3) of the cross section concerned. Steel Materials Used for Supporting Structures for Distribution Line Shaped steel, steel tubes, bolts and other structural steel members used for steel towers and iron poles shall conform to Article 103. Article 151 1. Load for Foundation of Supporting Structures of Distribution Lines and Safety Factor Installation of Foundations of Supporting Structures The foundation of a support of a distribution line shall be installed according to one of the followings: (1) The foundation shall be installed so that its safety factor is 2.0 or over to the load (wind load or assumed normal load) which the supporting structure should endure. However, the safety factor of foundation strength of a steel tower may be taken to be 1.33 or over to the assumed abnormal load. (2) A steel plate built-up pole or a steel tube pole that has a total length of 16 m or less and a design load of 7.0 kN or less or a wooden pole shall be embedded according to the total length divisions in Table 151-1. In a rice field or another place of soft ground, especially strong guy anchors shall be installed. Table 151-1 Embedment of iron pole Type A and wooden pole Total length division Embedment 15 m or less 1/6 or more of total length More than 15 m 2.5 m or more (3) A reinforced concrete pole that has a total length of 20 m or less and a design load of 15.0 kN or less shall be embedded according to the design load division and total length division in Table 151-2. However, if installed in a rice field or another place of soft ground, the pole shall be 16 m or less in total length and 7.0 kN or less in design load and especially strong guy anchors shall be installed. Table 151-2 Embedment of reinforced concrete pole Type A Design load division Total length division Embedment 15 m or less 1/6 or more of total length 7.0 kN or less More than 15 m and 16 m or less 2.5 m or more More than 16 m and 20 m or less 2.8 m or more More than 7.0 kN 14 m or more and 15 m or less (1/6 of total length + 30 cm) or more and More than 15 m and 20 m or less 2.8 m or more 10.0 kN or less (1/6 of total length + 50 cm) or more More than 10.0 kN 14 m or more and 15 m or less and More than 15 m and 18 m or less. 3.0 m or more 15.0 kN or less More than 18 m and 20 m or less 3.2 m or more 2. Calculation of Safety Factors for Foundation of Wooden Poles, Reinforced Concrete Poles and Iron Poles The safety factor of the foundation of a wooden, reinforced concrete or iron pole shall be calculated by the following formula: _________________________________________________________________________________________________________________________________________ Page 129 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) f KD0 t 4 120P(H t 0) 2 f: is the safety factor of the foundation of the supporting structure. D0 : is the diameter (m) of the supporting structure at the ground level. t: is the embedded depth (m) of the supporting structure. H: is the height (m) of the point of action of concentrated loads from the ground surface. P: is the load (N) converted into a concentrated load at the top of the supporting structure. t0 : is the depth (m) of the center of gyration of the supporting structure from the ground surface. t0 K: Normal soil Soft soil 3. (without guy anchor) 2 t ( m) 3 is the soil coefficient taking the value in Table 151-3. Table 151-3 Soil coefficient Classification of soil [A] Aggregated soil or sand, and soil with plenty of gravel or stone belonging under hard soil [B] Aggregated soil or sand, and soil with plenty of gravel or stone belonging under soft soil [C] Quicksand (with no soil mixed) [D] Moist clay, humus, fill and other soft soils (excluding deep rice fields) Soil coefficient (N/m4) 3.9×107 2.9×107 2.0×107 0.8×107 Reinforcement of Foundations of Supporting Structures The foundation of a supporting structure shall be reinforced and firmly held so that its safety factor is 2.0 or over. Article 152 Reinforcement for Supporting Structures of Distribution Lines by Guys and so on 1. Reinforcement of supporting structure by guys (1) Supporting structures other than steel towers may be guyed to share strength with the guys. In such a case, the strength of the supporting structure itself shall be such that it endures a half or more of the wind load. (2) If a medium-voltage overhead distribution conductor is installed in secondary proximity to or crossing condition with a building or the like (*1), supporting structures other than steel towers shall be fitted with a guy on the opposite side of the building. This guy may be omitted in the following cases: a. If the medium-voltage overhead distribution line forms a horizontal angle of 10 or more degrees away from the building. b. If the supporting structure of the medium-voltage overhead distribution line uses a Type B pole (*2) that endures the assumed normal load plus a horizontal lateral load of 2.0 kN or a Type B pole that endures 1.1 times the assumed normal load (*3). (*1) The term “building or the like” includes buildings, roads, pedestrian overpasses, _________________________________________________________________________________________________________________________________________ Page 130 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) telephone lines, and low-voltage overhead conductors. (2) 2. (*2) “Type B poles” include Type B iron poles and Type B reinforced concrete poles. (*3) The applicability of “Type B pole that endures 1.1 times the assumed normal load” is limited to the case where a cable is used for the electrical conductor or where each span between adjacent supporting structures is 75 m or less and insulated conductor is used for the line. In a straight section (*5) using 15 or more consecutive Type A poles (*4), guys shall be installed on both sides of the distribution line at intervals of 15 poles or less. (*4) “Type A Poles” includes Type A iron poles and Type A reinforced concrete poles. (*5) “Straight section” includes such a portion that forms a horizontal angle of 5 degrees or less. Installation and safety factor of guys Guys installed with the supporting structure of medium- or low-voltage overhead distribution line shall be installed as follows: (1) Upper part of the guy The metallic wire used for the guy shall be as follows: (2) a. The safety factor shall be 2.6 or over (*6). (*6) The safety factor shall be 1.5 or over for a guy installed with a wooden pole, iron pole Type A or reinforced concrete pole Type A. b. If a twisted conductor is used for the metallic wire, it shall have 3 or more strands and a minimum tensile strength of 10 kN or over. Portion near the ground For the portion near the ground, that is, from the underground portion of the guy installed with a reinforced concrete pole or iron pole to 30 cm above the ground, a galvanized iron rod or similar rod equal or superior to it in strength and corrosion resistance shall be used. (3) Foundation The guy anchor shall be installed firmly so that it can adequately endure the tensile load from the guy. A guy anchor installed with a supporting structure other than a wooden pole shall be of such a material that hardly corrodes. (4) Others a. If a guy installed on an overhead distribution line is in danger of touching an electrical conductor, an insulator or the like shall be inserted in the upper part of the guy. However, an insulator or the like need not be inserted if the guy is installed on a low-voltage overhead distribution line in a place other than a rice field or other swamp. b. A guy crossing a road shall have a height of 5 m or over from the road surface. If this is impossible for technical reasons, 4.5 m or over and 2.5 m or over above a sidewalk are allowed if there is no danger of interfering with traffic. _________________________________________________________________________________________________________________________________________ Page 131 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. Installation of wooden poles, Type A iron poles, and Type A reinforced concrete poles As shown in Table 150-2, the strength of a supporting structure does not anticipate the uneven component of tension in the distribution conductors. Therefore, if installed on a medium-voltage overhead distribution line where such an uneven tension acts, the wooden pole, Type A iron pole and Type A reinforced concrete pole shall be fitted with guys that endure that uneven tension, according to the following: (1) In a straight section (*7) of an electrical line where the difference in support span is large, guys that endure the horizontal force due to the uneven tension brought about by the span difference shall be installed on both sides of the electrical line. (*7) “Straight section” includes a portion forming a horizontal angle of 5 degrees or less. (2) In the portion of an electrical line exceeding 5 degrees in horizontal angle, a guy that endures the horizontal lateral component of the assumed maximum tension shall be installed. (3) At the place of anchoring all the conductors of a distribution line, a guy that endures the horizontal force of the uneven tension equal to the assumed maximum tension shall be installed. 4. Installation of supporting structures of tension-resistant or similar type in a medium-voltage overhead distribution line (1) Type B iron pole or Type B reinforced concrete pole Type B poles on a medium-voltage overhead distribution line shall be as follows: (2) a. If 10 or more poles for straight sections are used consecutively, one reinforced concrete pole or iron pole of the tension-resistant type shall be installed at every 10 poles (*8)or less. That pole shall allow for “the uneven” tension one third of the assumed maximum tension" of each electrical conductor and summed up over all the electrical conductors under the assumed normal load. (*8) When every 10 poles are difficult, this type can be installed for every 15 poles. b. If the support span exceeds 250 m, a supporting structure of the above-stated tension-resistant type shall be used for the supporting structure concerned. However, if a tension-resistant supporting structure is used at places adjacent to such a span of the distribution line, a supporting structure of the tension-resistant type need not be used for the supporting structure concerned depending on the ground conditions there. Iron tower a. If 10 or more towers for straight sections are used consecutively, one iron tower having tension-resistant insulator sets or another tower equal or superior to it in strength shall be installed. b. If the tower span exceeds 600 m, the tension resistant type shall be used for the tower concerned. However, if the tension-resistant type is used for the towers at places adjacent to such a span of the distribution line, the tension-resistant type need not be used for the tower concerned depending on the ground conditions there. 3-6-2-3 Regulation for Installation on Distribution Lines _________________________________________________________________________________________________________________________________________ Page 132 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 153 Height of Overhead Distribution Conductors The height of a medium- or low-voltage overhead distribution conductor shall conform to the following paragraphs if a bare conductor, insulated conductor or cable is used. 1. If crossing a road, the height shall be 6 m or more from the ground surface. 2. For cases other than the above, the height shall be 5.5 m or more from the ground surface. It shall be 4 m or over if a low-voltage overhead distribution conductor is installed in a place other than a road. 3. If it is installed above a pedestrian overpass, it shall be 3 m or over from the overpass surface for low-voltage overhead distribution conductors and 5.5 m or more from the overpass surface for medium-voltage overhead distribution conductors. However, if insulated conductor or cable is used, it may be reduced to 4 m from the ground surface. 4. The height of an electrical conductor installed over the water shall be 5 m or more from the highest water level if there is no navigation of vessels. If there is navigation, it shall be 2 m or over from the mast of a vessel at the highest water level. 5. If a low-voltage overhead distribution line carrying an operation voltage of 300 V or less and used for outdoor illumination is installed without interfering with the traffic, the height shall be 4 m or more from the ground surface. 6. For a low-voltage overhead distribution line installed under a bridge or other similar structures, the height may be reduced to 3.5 m from the ground surface in spite of the prescription of Paragraph 2. 7. If a medium-voltage overhead distribution line is installed in an urban area, the height shall be 10 m or more from the ground surface. The height may be reduced to 8.0 m from the ground surface if insulated conductor is used and 5.0 m if cable is used. For the one span of an overhead distribution line connecting the inside and outside of a hydropower station, substation or similar premises, the height need not be 10 m or more from the ground surface (*1). (*1) Article 154 1. From the ground surface, it shall be 8.0 m or more for insulated conductor and 5.0 m or more for cable. Regulation of Distribution Lines at Adjacency to and Crossing with Other Objects Minimum clearance between overhead distribution lines and other objects If a medium- or low-voltage overhead electrical conductor approaches to or crosses another object, it shall be installed with a clearance larger than the value prescribed in the following items except for the service drop line and indoor and outdoor user’s sites. (1) Adjacency to buildings Table 154-1 Adjacency to buildings _________________________________________________________________________________________________________________________________________ Page 133 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Facility involved Voltage Adjacency position (Apply if marked with Low-voltage Top structures of a building (roof, eaves, clothes-drying platform and other structures having the possibility of being climbed on by a person) A simple projecting signboard or the like installed on a building Insulated Bare conductor conductor 2.0 2.7 The case where the overhead electrical conductor is installed under a building (2) Type 2 Type 3 1.0 - - (In the case of secondary proximity) - Medium-voltage 2.5 3.0 1.2 Low-voltage 1.2 1.5 0.4 ○ (In the case of primary proximity) - ○ Lateral and downside adjacency Upside, lateral and downside adjacency with the electrical conductor not put in a protective device Upside, lateral and downside adjacency with the electrical conductor put in a protective device Medium-voltage 1.5 3.0 0.5 Low-voltage 0.4 0.6 0.4 (In the case of secondary proximity excluding downside adjacency) - ○ (In the case of primary proximity excluding downside adjacency) - ○ Medium-voltage Low-voltage Medium-voltage 1.5 3.0 0.5 Allowable unless contact occurs (In the case of secondary proximity excluding downside adjacency) - ○ (In the case of primary proximity excluding downside adjacency) - Same as upside, lateral and downside adjacency with the electrical conductor not put in a protective device 1.2 1.5 0.4 - - ○ Upside, lateral and downside adjacency Downside adjacency ○.) Cable ○ Upside adjacency Low-voltage Structures of a building other than those mentioned above Medium-voltage distribution line strengthening work Clearance (m) Medium-voltage 1.5 3.0 0.5 Low-voltage 0.6 1.0 0.3 (In the case of secondary proximity excluding downside adjacency) - Medium-voltage 1.5 3.0 0.5 - ○ (In the case of primary proximity excluding downside adjacency) - - Adjacency to or crossing with a road or pedestrian overpass Table 154-2 Adjacency to or crossing with road or pedestrian overpass Facility involved Road and pedestrian overpass Position of adjacency or crossing Upside and lateral adjacency Medium-voltage distribution line strengthening work Clearance (m) (Apply if marked with ○.) Voltage Low voltage Insulated conductor Horizontal 1.0 or 3.0 Medium voltage Horizontal 1.5 or 3.0 Bare conductor Cable Type 2 Type 3 3.0 Horizontal 1.0 or 3.0 - - 3.0 Horizontal 1.2 or 3.0 ○ (In the case of secondary proximity) ○ (In the case of primary proximity) _________________________________________________________________________________________________________________________________________ Page 134 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Upside crossing Downside adjacency (3) Low voltage Medium voltage Low voltage Medium voltage - - ○ - 0.3 - - 0.5 - - Conform to Article 153. 0.6 1.5 Do not install. Adjacency to or crossing with an overhead telecommunication line Table 154-3 Adjacency to or crossing with an overhead telecommunication line Facility involved Overhead telecommunication line Position of adjacency or crossing Upside crossing (*1) Medium voltage Low voltage Medium voltage Low voltage (Apply if marked with ○.) Insulated conductor Bare conduct or Cable Type 2 Type 3 0.6 1.0 0.3 - - 1.0 2.0 0.5 0.6 1.0 0.3 ○ (In the case of secondary proximity) - 1.0 2.0 0.5 ○ - 0.3 - - Horizon tal 3.0 - - 0.3 - - 0.5 - - ○ (In the case of primary proximity) - Downside crossing (*2) Low voltage Medium voltage 0.6 Horizontal 3.0 (reinforcemen t of overhead telecommunic ation line) 0.6 1.0 (protective device) (*3) Adjacency Low voltage 0.3 0.6 0.3 - - Adjacency and crossing Medium voltage 1.0 2.0 0.5 - - Downside adjacency (*1) Supporting structure of overhead telecommunication line Voltage Low voltage Upside and lateral adjacency Medium-voltage distribution line strengthening work Clearance (m) Medium voltage Do not install. Do not install. The medium-voltage overhead distribution conductor shall not be installed in downside adjacency circumstances with an overhead telecommunication line. However, it may be installed by one of the following if the horizontal clearance between the medium-voltage overhead distribution line and overhead telecommunication conductor is 3 m or more. (*2) a. If cable is used for the medium-voltage overhead distribution conductor. b. If insulated conductor is used for the medium-voltage overhead distribution conductor and the overhead telecommunication conductor have a tensile strength of 10 kN or more and their supporting structures are reinforced to a strength equal or superior to the strength of the supporting structures of the medium-voltage overhead distribution line. The medium-voltage overhead distribution conductor shall not be installed in downside crossing with an overhead telecommunication conductor. However, it may be installed if installed by one of the following: _________________________________________________________________________________________________________________________________________ Page 135 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (4) a. If cable is used for the medium-voltage overhead distribution conductor. b. If insulated conductor is used for the medium-voltage overhead distribution conductor and a strong protective device earthed by earthing work Type D in Article 57-2 is installed for the metallic parts between the medium-voltage overhead distribution conductor and overhead telecommunication conductor. (*3) The structure of the protective device shall conform to Article 148-2. Adjacency to antenna Table 154-4 Adjacency to antenna Facility involved Television antenna or the like (an antenna installed in the form of an electrical conductor is included under overhead telecommunication conductor.) Adjacency position Voltage Upside and Lowlateral voltage adjacency Downside adjacency Medium-voltage distribution line strengthening work (Apply if marked with ○.) Clearance (m) Insulated conductor Bare conductor Cable Type 2 Type 3 0.6 1.0 0.3 - - Mediumvoltage 1.0 2.0 0.5 ○ (In the case of second ary proximi ty) Low-volt age 0.6 1.0 0.3 - Mediumvoltage ○ (In the case of primary proximity) - A medium-voltage overhead distribution conductor shall not installed under an antenna and within the horizontal clearance equal to the antenna pole height from the ground surface. _________________________________________________________________________________________________________________________________________ Page 136 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (5) Adjacency to or crossing with other medium- and low-voltage overhead distribution conductors Table 154-5 Adjacency to or crossing with other medium- and low-voltage overhead distribution conductors Medium-voltage electrical line strengthening work (Apply if marked with Electrical line installed upside Clearance (m) Facility involved Mutual adjacency or crossing of low-voltage overhead distribution conductors Mutual adjacency or crossing of medium-voltage overhead distribution conductors Adjacency or crossing of a medium-voltage overhead distribution conductor installed upside or laterally and a low-voltage overhead distribution conductor. Adjacency of a medium-voltage overhead Electrical line installed downside or laterally Insulated conductor Bare conductor Cable ○.) Insulated conductor 0.6 1.0 0.3 Bare conductor 1.0 1.0 0.6 Cable Type 2 0.3 0.6 0.3 Supporting structure 0.3 0.3 0.3 Insulated conductor Bare conductor Cable 1.0 2.0 1.0 2.0 2.0 2.0 0.5 2.0 0.5 Supporting structure 1.0 2.0 0.5 Insulated conductor Bare conductor Cable 1.0 2.0 0.5 2.0 2.0 2.0 0.5 2.0 0.5 Supporting structure 1.0 2.0 0.5 Insulated conductor Bare conductor Cable Horizontal 3.0 (low-voltage Installation not allowed Horizontal 3.0 Type 3 - - ○ (If installed upside or laterally) - ○ ○ (In the case of secondary proximity and crossing) (In the case of primary proximity ) - - _________________________________________________________________________________________________________________________________________ Page 137 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) distribution conductor installed downside to a low-voltage overhead distribution conductor (*4) Crossing of a medium-voltage overhead distribution conductor installed downside with a low-voltage overhead distribution conductor (*5) (*4) reinforced) Supporting structure Insulated conductor Bare conductor Cable Supporting structure 1.0 (protective device) (*6) Installation not allowed 0.5 - - A medium-voltage overhead distribution conductor shall not be installed in downside adjacency circumstances to a low-voltage overhead distribution conductor. However, it may be installed by one of the following if the horizontal clearance from the medium-voltage overhead distribution conductor and low-voltage overhead distribution conductor is 3 m or more. (*5) a. If cable is used for the medium-voltage overhead distribution conductor. b. If insulated conductor is used for the medium-voltage overhead distribution conductor and the low-voltage overhead distribution conductor have a tensile strength of 10 kN or over and their supporting structures are reinforced to a strength equal or superior to that of the supporting structures of the medium-voltage overhead distribution conductor. A medium-voltage overhead distribution conductor shall not installed in downside crossing with a low-voltage overhead distribution conductor. However, it may be installed if installed by one of the following: a. If cable is used for the medium-voltage overhead distribution conductor. b. If insulated conductor is used for the medium-voltage overhead distribution conductor and a strong protective device earthed by earthing work Type D in Article 57-2 is installed at the metallic parts between the medium-voltage and low-voltage overhead distribution conductors. (*6) The structure of the protective device shall conform to Article 148-2. (6) Adjacency to and crossing with a facility other than Item (1) to Item (5) Table 154-6 Adjacency to and crossing with other facilities [other than Item (1) to Item (5)] Facility involved Top structure of a building Position of adjacency or crossing Upside adjacency and Medium-voltage distribution line strengthening work Clearance (m) Voltage Low voltage (Apply if marked with ○.) Insulated conductor Bare conductor Cable Type 2 Type 3 2.0 2.7 1.0 - - _________________________________________________________________________________________________________________________________________ Page 138 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) upside crossing ○ Medium voltage 2.0 2.0 Low voltage 0.6 1.0 ○ 1.2 (In the case of secondary proximity or upside crossing) (In the case of primary proximity) 0.3 - - ○ Lateral and downside adjacency Simple signboard jutting out of a building, and another structure with no danger of being climbed on by a person, or facility other than a building Upside, lateral and downside adjacency and upside crossing with the electrical conductor not put in a protective device Upside, lateral and downside adjacency and upside crossing with the electrical conductor put in a protective device Medium voltage 1.0 2.0 0.5 Low voltage 0.6 1.0 0.3 The case where the overhead electrical conductor is installed under another facility (7) Upside, lateral and downside adjacency and upside crossing Downside crossing (In the case of primary proximity excluding downside adjacency) - - ○ Medium voltage Low voltage Medium voltage Low voltage Structure other than the above ○ (In the case of secondary proximity excluding downside adjacency or upside crossing) 1.0 2.0 0.5 ○ (In the case of secondary proximity excluding downside adjacency or upside crossing) (In the case of primary proximity excluding downside adjacency) - - Allowable unless contact occurs Same as upside, lateral and downside adjacency and upside crossing with the electrical conductor not put in a protective device 0.6 1.0 - 0.3 - ○ ○ (In the case of secondary proximity excluding downside adjacency or upside crossing) (In the case of primary proximity excluding downside adjacency) Medium voltage 1.0 2.0 0.5 Low voltage 0.6 1.0 0.3 - - Medium voltage 1.0 2.0 0.5 - - Adjacency to plants Table 154-7 Adjacency to plants Facility involved Adjacency position Medium-voltage distribution line strengthening work (Apply if marked with Clearance (m) Voltage ○.) Insulated conductor Bare conductor Cable Type 2 Type 3 _________________________________________________________________________________________________________________________________________ Page 139 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Low voltage Upside and lateral adjacency Plant Medium voltage Shall not contact due to ordinarily blowing wind or the like. 0.5 2.0 Shall not contact due to ordinarily blowing wind or the like. 2. Medium-voltage distribution line strengthening work (1) Facilities requiring medium-voltage distribution line strengthening work - - - - If the medium-voltage distribution conductor is installed in adjacency or upside crossing condition with another facility conforming to Table 154-8, it shall be installed using medium-voltage distribution line strengthening work. However, if the facility is an object other than a building or the like (*7), medium-voltage overhead distribution line strengthening work shall be applied only if the medium-voltage overhead distribution conductor may endanger persons due to its contact with that facility if an electrical conductor of the medium-voltage overhead distribution line is broken or the supporting structure collapses. (*7) The term “building or the like” includes a building, road, pedestrian overpass, overhead telecommunication line, antenna, low-voltage overhead distribution conductor, another medium-voltage overhead distribution conductor, and medium- and high-voltage overhead power transmission conductors. Table 154-8 Installation conditions requiring medium-voltage distribution line strengthening work Type of medium-voltage distribution line strengthening work Type 2 Type 3 (2) Installation conditions of overhead distribution conductor If installed jointly with an overhead telecommunication conductor If installed in secondary proximity excluding downside adjacency to a building If installed in upside or lateral secondary proximity to a road or pedestrian overpass If crossing over a road or pedestrian overpass If installed in upside or lateral secondary proximity to a low-voltage overhead distribution conductor or the like If crossing over a low-voltage overhead distribution conductor If installed in secondary proximity to another type of facility If installed in primary proximity to a building If installed in primary proximity to a road or pedestrian overpass If installed in primary proximity to an overhead telecommunication conductor If installed in upside or lateral relation with another medium-voltage distribution conductor If installed in primary proximity to another type of facility Type 2 medium-voltage distribution line strengthening work Medium-voltage distribution line strengthening work shall be as follows: a. b. (3) A wooden pole used as a supporting structure shall have a safety factor to wind load of 2.0 or over according to Table 150-2. The span of an overhead distribution line shall conform to Table 149-1. c. The insulator set used where the electrical conductor approaches or crosses another facility shall conform to Article 140-4-(2) d. The electrical conductor shall be installed in such a manner that there is no danger of forming a short circuit due to wind-induced wire sway. Type 3 medium-voltage distribution line strengthening work Type 3 medium-voltage distribution line strengthening work shall be as follows: _________________________________________________________________________________________________________________________________________ Page 140 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 3. a. The span of an overhead distribution line shall conform to Table 149-1. b. The electrical conductor shall be installed in such a manner that there is no danger of forming a short circuit due to wind-induced wire sway. Installation in urban areas or the like If a medium-voltage overhead distribution line is to be installed in an urban area, it shall be installed according to the following items so that there is no danger. However, the following items are not necessarily adhered to if cable is used for the electrical conductor. The definition of an urban area or another densely populated area is given in Article 111. (1) Strength of distribution conductor A medium-voltage distribution conductor shall have a tensile strength of 30 kN or more pursuant to Article 145. (2) Supporting structure (3) The supporting structure of a medium-voltage electrical line shall be reinforced concrete poles, iron poles or steel towers. Height of distribution conductor above ground surface The height of the medium-voltage distribution conductor shall be as shown in Article 153-7. (4) Restrictions on span The span of a medium-voltage overhead distribution line shall be as shown in Table 149-1. 3-6-2-3 Particularities of Distribution Lines for Joint Use and Side-by-side Use with Other Objects Article 155 1. Joint Use and Side-by-side Use of Distribution Lines with Other Objects Joint Installation of Low-voltage and Medium-voltage Overhead Distribution Conductors If low-voltage and medium-voltage overhead distribution conductors are installed on the same supporting structure, the following items shall be adhered to. (1) The low-voltage overhead distribution conductor shall be installed under the medium-voltage overhead distribution conductor and on separate cross arms. (2) The clearance between low-voltage and medium-voltage overhead distribution conductors shall be 1.2 m or more (*1). However, if installed on a corner pole, branch pole or the like where there is no possibility of erroneous contact, the clearance of 1.2 m or more is not necessarily adhered to. (*1) If cable is used for the medium-voltage overhead distribution conductor, the clearance shall be 50 cm or more. _________________________________________________________________________________________________________________________________________ Page 141 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 2. Joint Installation of Low-voltage and Medium-voltage Overhead Distribution Conductors and Overhead Telecommunication Conductors If a low-voltage and medium-voltage overhead distribution conductor and an overhead telecommunication conductor are to be installed on the same supporting structure, they shall be installed according to the following items: (1) The overhead distribution line shall be given Type 2 medium-voltage distribution line strengthening work. (2) The overhead distribution conductor shall be installed over the overhead telecommunication conductor and on separate cross arms. (3) The medium-voltage overhead distribution conductor shall use cable or electrical conductor with a tensile strength of 30 kN or more . (4) The clearance between overhead distribution conductors and telecommunication conductors shall be 75 cm or more for low voltages and 2.0 m or over (*2) for medium voltages. (*2) (5) If cable is used for the medium-voltage overhead distribution conductor, the clearance shall be 50 cm or more. If vertical wiring (*3) of an overhead distribution line and of an overhead telecommunication line are to be installed on the same supporting structure, they shall be installed with the supporting structure in between and the vertical wiring of the overhead distribution line shall not jut out on the road side. However, they may be installed on the same side of the supporting structure if the situation falls under any of the following: (*3) “Vertical wiring” includes the distribution conductor or telecommunication conductor installed in the longitudinal direction of the supporting structure and its accessories. a. If the vertical wiring of the overhead distribution line is 1 m or more distant from the vertical wiring of the overhead telecommunication line. b. If the vertical wiring of the overhead distribution line and overhead telecommunication line are cable and they are firmly supported on the supporting structure or cross arms so that there is no danger of direct contact between them. (6) Vertical wiring of the overhead distribution line shall use insulated conductor or cable for low voltages and cable for medium voltages in the section from 2 m above the overhead telecommunication conductor to the lowest portion. (7) Items (2) and (4) shall not necessarily apply to vertical wiring of the overhead telecommunication conductor if approval of the managers of both parties are obtained and if that vertical wiring is cable or is put in an object with sufficient dielectric strength so that it will not come in direct contact with the overhead distribution conductors. 3-6-3 Article 156 1. Service Drop Lines Overhead Service Drop Lines Low-voltage overhead service drop lines Low-voltage overhead service drop lines shall be installed in accordance with the following items: (1) Electrical conductor _________________________________________________________________________________________________________________________________________ Page 142 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) a. The electrical conductor shall be of insulated conductor or cable. b. The electrical conductor shall have a tensile strength of 3.0 kN or more unless it is cable. However, a tensile strength of 2.0 kN or more may be allowed only if the span is 15 m or less. The typical conductors are listed in Table 156-1. Hard copper 2.0kN(2.0mm) 3.0kN(2.6mm) (2) (3) Table 156-1 The typical conductors Annealed copper Hard copper Hard aluminum stranded stranded 8mm2 3.5mm2 3.5mm 2 14mm 5.5mm2 4.5mm ACSR 12mm2 12mm2 Height from ground a. The height shall be 5 m or over (*1) from the road surface if the conductor crosses a road. (*1) If it is difficult to secure 5 m or more from the ground surface for technical reasons, 3 m from the road surface is allowable if this height does not hinder the traffic. b. If installed over a pedestrian overpass, the height shall be 3 m or more from the overpass surface. c. The height shall be 4 m or more (*2) from the ground surface for cases other than a. and b. (*2) If it is difficult to secure 4 m or more from the ground surface for technical reasons, 2.5 m is allowable if this height does not hinder the traffic. Clearance to other objects A low-voltage overhead service drop line shall be installed according to Article 154-1. For a building in which a low-voltage overhead service drop line is directly drawn, or if it is technically difficult to install such facilities according to the provisions of Article 154-1, the clearance to other objects may be equal to or larger than the value prescribed in Table 156-2. If the electrical conductor is insulated conductor, it shall be installed in such a manner that a person cannot reach it even if he or she stretches out his/her hand from a window, corridor, clothes-drying platform or a passage to one or other ordinarily accessible place. Object Table 156-2 Clearance from low-voltage overhead service drop line to other facilities Clearance (m) Building directly drawing in a service drop line If the facility is other than a road, pedestrian overpass, or lowor Top structure of medium-voltage distribution conductor, a building and it is technically difficult to install a service drop line according to the Other than the prescriptions of Article 154-1, and there is above no possibility of danger If the facility is other than a building directly drawing in a low-voltage overhead service drop line and it is technically difficult to install according to the prescriptions of Article 154-1, and there is no possibility of danger and the service drop line is to be installed near the attaching point to the customer’s site Allowable if installed so that there is no possibility of danger 2 m or over above the top structure if the electrical conductor is insulated conductor and 0.5 m or over if it is cable 0.15 m or over to the side or under the top structure if the electrical conductor is insulated conductor or cable 0.15 m or over if the electrical conductor is insulated conductor or cable Another building (if there is no possibility of a person’s touching it) or telecommunication conductor shall not come into contact. 0.15 m or over above and 0.1 m or over to the side of a lead-in wire anchor (called the anchor hereafter) of a telecommunication conductor or the like _________________________________________________________________________________________________________________________________________ Page 143 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 0.1 m or over above and to the side of a telecommunication conductor or the like in the section within 25 cm on the power source side of a wire anchor 2. Medium-voltage overhead service drop lines Medium-voltage overhead service drop lines shall be installed according to the following items: (1) Electrical conductor Insulated conductor with a tensile strength of 10 kN or more or cable shall be used. (2) Other installation method a. Height of service drop line To the height of a medium-voltage overhead service drop line, the provisions for medium-voltage overhead distribution conductors in Article 153 shall apply. However, the height may be reduced to 4.0 m above the ground surface if it is installed in a place other than that of over and above road or pedestrian overpass and the conductor is cable. b. Adjacency and crossing of service drop lines with other objects To the clearance from a medium-voltage overhead service drop line to another object, the provisions of Article 154 shall apply. For a building in which a low-voltage overhead service drop line is drawn, no particular regulations are provided for on the clearance to another building or the like as long as there is no danger. Article 157 1. Exterior Wall Lines at Consumer Facilities Low-voltage exterior wall service drop lines Low-voltage exterior wall service drop lines shall be installed by insulator work (*1), synthetic resin tube work, metal tube work (*2), bus duct work or cable work. (1) (*1) "Insulator work" is limited to open places. (*2) "Metal tube work" is limited to installation on a building other than timber construction. (*3) "Bus duct work" is limited to installation on a building other than timber construction and places other than inaccessible concealed places. Insulator work Low-voltage exterior wall service drop lines installed by insulator work according to Article 177 shall conform to the following. In addition, they shall be installed in such a manner so as to exclude the possibility of a person touching it easily. a. The electrical conductor shall be of insulated conductor (*4) with a tensile strength of 2.0 kN or more. (*4) "Insulated conductor" excludes PVC-insulated conductor. b. The spacing between electrical conductors and the clearance from a wire to the building on which the low-voltage exterior wall service drop line is installed shall be at least the value prescribed in Table 157-1 depending on the rain shield conditions there. _________________________________________________________________________________________________________________________________________ Page 144 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Table 157-1 Spacing between electrical conductors of low-voltage exterior wall service drop lines installed by insulator work Place not exposed to rain Place exposed to rain (2) Spacing between wires (cm) 300 V or less More than 300 V 6 6 6 12 Clearance to building part (cm) 300 V or less More than 300 V 2.5 2.5 2.5 4.5 c. The clearance between conductor supports shall be 2 m or less. d. PVC-insulated conductor may be used or the clearance between conductor supports may exceed 2 m but is limited to 15 m only if the low-voltage exterior wall service drop line is installed using an electrical conductor with a tensile strength of 2.0 kN or more and keeping the spacing between electrical conductors to 20 cm or more and the clearance from an electrical conductor to the building part on which it is installed to 30 cm or more. Synthetic resin tube work Low-voltage exterior wall service drop lines to be installed by synthetic resin tube work according to Article 177 shall be installed as follows: (3) a. There shall be no connection point of electrical conductors in the synthetic resin tube. b. The synthetic resin tube shall not be installed in a place where there is danger of receiving the pressure of a heavy object or severe mechanical shocks. If, however, an appropriate protective device is installed, such place may not be excluded from installing the synthetic resin tube. c. (a) Connection and support of tubes and accessories shall be made as follows: Synthetic resin tubes and accessories shall be firmly joined by insertion connection with the tube insertion depth equal to or greater than 1.2 times the outer diameter of the tubes (*5). In addition, the joint shall be firmly supported on the building or the like by appropriate means. (*5) If an adhesive is used, the insertion depth shall be of 0.8 or more times the outer diameter. (b) If the synthetic resin tube is supported by saddles or the like, the supporting clearance shall be 1.5 m or less. In addition, a support shall be provided near the tube ends, the connection point between tube and box, and the connection point between tubes. Metal tube work The low-voltage exterior wall service drop line installed by metal tube work according to Article 177 shall be installed as follows: (4) a. There shall be no connection point of electrical conductors in the metal tube. b. The connection between metal tubes or between a metal tube and box or similar object shall be accomplished by a screw joint or other equal or superior method to make a firm and electrically perfect connection. Bus duct work _________________________________________________________________________________________________________________________________________ Page 145 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The low-voltage exterior wall service drop line installed by bus duct work according to Article 177 shall be installed as follows: (5) a. The bus duct shall be supported firmly at intervals of 3 m or less (*6). (*6) The intervals shall be of 6 m or less if it is installed vertically in a place prepared in such a manner that no person other than the operator has access there. b. The connection between ducts shall be firm and electrically perfect. b. The bus duct of a non-ventilation type shall be closed at both ends so that dust hardly gets inside it. Cable work The low-voltage exterior wall service drop line by cable work according to Article 177 shall be installed as follows: a. Cables installed in places subject to the pressure of a heavy object or severe mechanical shocks shall be protected with a metal tube or gas iron tube. b. If an electrical conductor is to be installed along the bottom face or a side face of a building, its supporting clearance shall be 2 m or less (*7) and it shall be installed so as not to damage its covering if it is cable. (*7) In a place where there is no danger of a person’s touching it, the clearance shall be 1 m or less. c. If the cable is to be installed in a state which is suspended from a messenger wire, it shall be installed in such a manner that the electrical conductor will not touch the building on which the low-voltage exterior wall service drop line is installed. 2. Medium-voltage exterior wall service drop lines (1) These shall be installed using cable for the electrical conductor in an open place as follows: The cable shall be put in a rugged tube or trough or otherwise installed so that there is no danger of a person touching it. (2) If the cable is to be installed along the bottom or a side of a building , its support span shall be 2 m or less (*8). In addition, it shall be installed so as not to damage its covering. (*8) The span shall be 6 m or less if installed vertically. (3) If the cable is to be installed in a state which is suspended from a messenger wire, it shall be installed in such a manner that the electrical conductor will not touch the building on which the medium-voltage exterior wall service drop line is installed. (4) Earthing work Type A (*9) of Article 57-2 shall be given to the metallic part of the tube or other protective device in which the cable is put, the metallic wire connecting box and the metallic sheath of cable. (*9) Earthing work Type D shall be given to the sheath if it is installed in such a manner that there is no danger of a person touching the conductor. Article 158 Party Service Drop Lines For a low-voltage service drop line, a party service drop line may be installed to avoid service _________________________________________________________________________________________________________________________________________ Page 146 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) line congestion above ground in a densely populated area. For a medium-voltage service drop line, however, a party service drop line shall not be installed. Low-voltage party service drop lines shall be installed according to the provisions of Article 156. In addition, the following paragraphs shall be adhered to in installation. 1. The service drop line extension shall not exceed 100 m from the branch. 2. It shall not cross over a road 5 m or more in width. 3. It shall not pass through a building. 3-6-3 Article 159 1. Power Meterings Power Meterings Authorization of Power Meterings Power Meterings (hereafter called “meters”) shall be tested in respect of its structure and Properties based on IEC 60521 (1988-03) [Class 0.5, 1 and 2 alternating-current watt-hour meters] in Table 159-1:one by one and its term of validity is fixed. Fair and equitable energy transactions are expected by permitting the use of such meters with the term of validity so fixed. Table 159-1 Class of meter accuracy Class Application 0.5 Meter with transformer for High-voltage 1.0 Meter with transformer for Medium-voltage 2.0 Single meter and meter with transformer for Low-voltage 2. Installation of Single Meterings In installing single meters (*1), the following items shall be adhered to as to a place and position of installation, adjacency to wiring, and the mounting board of the exterior wall meter panel. (*1) (1) The term “single meter” refers to a meter used by itself and not in combination with an instrumental transformer. Place of installation a. Place where there is no fear of potential difficulty in meter reading or replacement work because of future new construction or reconstruction of a building; b. Place where there is no danger of induced damage; c. Place where there is little influence of vibrations; d. Place where there is little smoke or dust; e. Place where there are little temperature variations; f. Place not subject to corrosive action of chemicals or the like; g. Place where there is little influence of magnetism; h. Place of low humidity or free of moisture; i. Place not hindering traffic; _________________________________________________________________________________________________________________________________________ Page 147 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) j. Outdoor place allowing easy meter reading and work; Or, an open place allowing a person easy access without taking off his or her footwear if installed indoors because of some technical difficult, and k. (2) Place where there is no other hindrance Position of installation a. The position of installation of a single meter shall be on the power source side of the service entrance switch. It needs not be on the power source side of the service entrance switch if meters are installed for individual households of an apartment house or the like and there are difficulties in work. b. The indicator (*2) of a meter shall be at a height of 1.6 m from the ground surface. If there are difficulties in work, the height may be 1.6 m or more and 1.8 m or less within the limits of not hindering meter reading and work. (*2) c. (3) For the indicator of an electronic power meter, its display center shall be at a height of 1.6 m above the ground surface. If meters are to be installed for individual customers in an apartment house or the like, they shall be installed in the corridor or other place where easy meter reading is possible even when the customer is absent. Wiring near the meters a. The wiring of a single meter shall be arranged so that the power source side comes on the left side of the meter as you face it and the load side comes on the right side, and the wiring on the power source side and on the load side shall not cross near the terminals of the meter. b. (4) The wiring on the power source side and on the load side shall not be put in the same synthetic resin or metallic tube. Mounting board of outdoor meter panel a. The meters and its outdoor meter panels shall be attached to a wood or synthetic resin board 15 mm or more in thickness to avoid leaning or be attached firmly to a pole or other building. 3. Installation of Meterings with transformers In installing the instrumental transformer of a meter with a transformer (*3) or the like, the following items shall be adhered to as to its place and position of installation and its Properties, and in installing the meter with a transformer itself. (*3) (1) The term “meter with a transformer” refers to a meter used in combination with a voltage transformer, current transformer or voltage and current transformer. Place of installation of instrumental transformer The place of installation of an instrumental transformer shall be as follows: a. For low voltages Between the first lead-in support and service entrance switch _________________________________________________________________________________________________________________________________________ Page 148 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. For medium voltages (a) If drawn from the distribution line directly into the power receiving room Between the first support and service entrance switch (b) If drawn from the distribution line into the power receiving room via private poles On the first private pole, unless otherwise decided However, on the power source side of the service entrance switch and surge arrester if installed in the power receiving room or the like (2) Position of installation of instrumental transformer For the instrumental transformer, a position of easy replacement and inspection shall be chosen and it shall be installed there as follows: a. Low-voltage current transformer 2.5 m or over and 3.5 m or less above the ground surface if installed outdoors, and 2.3 m or over and 3.5 m or less above the floor if installed indoors b. Medium-voltage transformer If a medium-voltage transformer is to be installed in a place other than the power receiving and transformer station (room) of the customer site, it shall be installed according to one of the following: (a) If the transformer is to be installed on a pole, it shall be installed at a height of 5 m or over above the ground surface so that there is no danger of a person touching it. (b) If the transformer is to be installed on the ground in the yard or on the exterior wall or roof of a factory or the like, an appropriate fence shall be furnished around the transformer so that there is no danger of a person touching it. (c) If the transformer is to be installed on ground other than in the yard of a factory or the like, an appropriate fence shall be furnished around the transformer so that there is no danger of a person touching it. The sum of fence height and clearance from fence to live part shall be 5 m or more. In addition, a warning of danger shall be posted. The transformer shall be installed in a cubicle or the like earthed by earthing work Type A of Article 57-2 so that no live part will be exposed. (d) (3) Properties of instrumental transformer The instrumental current transformer (CT) shall be installed in accordance with IEC 61869-1 (2012) [Instrument transformers – Part 1: Current transformers], and the instrumental voltage transformer (VT) in accordance with IEC 61869-2 (2012 ) [Instrument transformers – Part 2: Inductive voltage transformers]. (4) Place of installation of meters with transformers The provisions of Paragraph 2-(1) shall apply correspondingly to the place of installation. Additional conditions are imposed as follows: (5) a. Place allowing easy meter reading, measuring and replacement work b. Indoors in principle, if the meter is used for a contract demand of 500 kW or more Position of installation of meter with transformers _________________________________________________________________________________________________________________________________________ Page 149 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) The height of the indicator (display center in case of an electronic combined meter) shall be 1.6 m. However, if it is installed in a power receiving room, meter cubicle or the like, the height may be 1.6 m or less. 3-6-4 Article 160 1. Underground Distribution Lines Properties of Underground Distribution Cables and Jointing Properties of underground distribution cables The term “cable” refers to a conductor covered with an insulator and further covered by a protective layer. Its Properties shall conform to the following items: (1) Properties of cable conductors, insulators and protective coverings The Properties of the conductor, insulator and protective covering of an underground distribution cable shall conform to the following: a. Cable conductor The copper or aluminum used for the cable conductor shall conform to IEC 60228 (1978-01) [Conductors of insulated cables] as to electric conductivity and tensile strength per unit area. The tensile strength and elongation of annealed copper wire and annealed aluminum wire shall be as shown in Table 160-1. Table 160-1 Tensile strength and elongation of cable conductors Single wire type Annealed copper wire Annealed aluminum wire d: b. Single wire diameter (mm) 0.10 or over and 0.28 or less Exceeding 0.28 and 0.29 or less Exceeding 0.29 and 0.45 or less Exceeding 0.45 and 0.70 or less Exceeding 0.70 and 1.6 or less Exceeding 1.6 and 7.0 or less Exceeding 7.0 and 16.0 or less 2.0 or over and 5.2 or less Exceeding 5.2 and 7.0 or less Tensile strength (N/mm2) 196 or over and less than (462-10.8d) 59 or over and less than 98 Elongation (%) 15.0 or over 20.0 or over 20.0 or over 20.0 or over 25.0 or over 30.0 or over 35.0 or over 10.0 or over 20.0 or over Denotes the diameter (mm) of the single wire. Cable insulator The cable insulator thickness shall conform to Table 144-2 or 144-3 for XLPE insulators and Table 144-4 for PVC insulators. c. Cable protective covering The cable protective covering thickness shall conform to Table 160-2. Table 160-2 Thickness of cable protective covering Type of cable protective covering Cable using PVC insulator Thickness of protective covering (mm) D 0.8 15 (1.5 if less than 1.5) _________________________________________________________________________________________________________________________________________ Page 150 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Thickness of protective covering (mm) Type of cable protective covering Cable using XLPE insulator Notes: (a) Triplex cable D 1.0 15 (1.5 if less than 1.5) Others D 1.3 25 (1.5 if less than 1.5) D denotes the inner diameter of the protective covering for round cross sections and the sum of inner major and inner minor axes of the protective covering divided by 2 for other cross section forms (mm). (b) The thickness of the protective covering shall be rounded off to one decimal place. (2) Dielectric strength of cables a. Low-voltage cables Low-voltage cables shall have the insulating capability according to IEC 60502-1 (1998-11) [Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um=1,2 kV) up to 30 kV (Um=36 kV) – Part 1: Cables for rated voltages of 1 kV (Um=1,2 kV) and 3 kV (Um=3,6 kV)] and related IEC standards or shall endure the test voltage prescribed in Table 160-3 if that voltage is impressed for one continuous minute between conductors and between a conductor and ground (*1) after immersion in fresh water for one hour. In addition, impress a direct voltage of 220 V for one minute between a conductor and ground. The insulation resistance value measured thereafter shall be equal to or greater than the value prescribed in Table 144-6. (*1) For single-core cables, only between the conductor and ground Table 160-3 Test voltage for low-voltage cables Conductor Stranded (nominal sectional area mm2) 8 or less More than 8 and 30 or less More than 30 and 80 or less More than 80 and 400 or less More than 400 b. Single wire (diameter mm) 3.2 or less More than 3.2 and 5 or less Test voltage (alternating V) 1,500 2,000 2,500 3,000 3,500 Medium-voltage cables Medium-voltage cables shall have the insulating capability according to IEC 60502-2 (1998-11) [Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um=1,2 kV) up to 30 kV (Um=36 kV) – Part 2: Cables for rated voltages from 6 kV (Um=7,2 kV) and 30 kV (Um=36 kV)] and related IEC standards or shall endure the test voltage given in Table 160-4 for 10 minutes when subjected to the dielectric strength test according to Article 147. Table 160-4 Test voltage for medium-voltage cables Place of test voltage impression Test voltage Alternating voltage 1.25 times the highest voltage or Between circuit and ground direct voltage twice the alternating test voltage 2. Connection of underground power distribution cables Straight connection and terminating connection of cables shall conform to the provisions of _________________________________________________________________________________________________________________________________________ Page 151 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 146. Article 161 Installation of Underground Distribution Cables 1. Installation methods of underground distribution cables (1) Electrical conductor Cable shall be used for the electrical conductor of an underground distribution line. (2) Work methods Underground distribution lines shall be installed by means of ductwork, culvert or direct burial. a. Ductwork The structure of the ductwork shall be as follows: b. (a) The duct used shall endure the pressure of vehicles or other heavy objects. The depth shall not be 0.8 m or less under a roadway or 0.6 m or less under a sidewalk. (b) The inner surface of the duct shall not have protrusions that may damage the cable. Culvert The structure of the culvert shall be as follows: c. (a) The culvert used shall endure the pressure of vehicles or other heavy objects. The depth shall not be 0.8 m or less under a roadway or 0.6 m or less under a sidewalk. (b) The underground distribution conductors shall be provided with a fireproof device or an automatic extinguishing facility shall be installed in the culvert. Direct burial If installed by direct burial, the cable burial depth shall be equal to or greater than the value in Table 161-1 and the cables shall be put in a strong trough or other protective shield. Table 161-1 Cable burying depth Cable burying place Place subject to pressure of vehicles or other heavy objects Places other than the above (3) Burying depth 1.2m 0.6m Installation of underground boxes Underground boxes (manholes, hand holes or the like) shall have the following structure: a. The underground box shall have a strong structure capable of enduring the pressure of vehicles or other heavy objects. b. For an underground box installed in a place where there is a danger of permeation of explosive or nonflammable gases and having a volume of 1 m3 or more, a ventilator or other gas-exhausting device shall be installed. c. The lid of an underground box shall be installed in such a manner that it cannot be easily opened by a person other than the installer. _________________________________________________________________________________________________________________________________________ Page 152 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) d. 2. The underground box has a structure that can drain the standing water inside it. Earthing of metals for sheath and the like Earthing work Type D of Article 57-2 shall be given to the metallic part of the duct, culvert or other protective device in which the underground distribution conductors are put, and the metallic wire-splicing box and the metal used for the sheath of underground distribution conductors. (*1) (*1) Article 162 Earthing work Type D of Article 57-2 need not be given if anticorrosive measures are taken. Indication of Buried Distribution Cables If a medium-voltage underground distribution line is installed in a duct or trough, the name, manager name and voltage (*1) of the buried object shall be indicated at intervals of about 10m. However, for a medium-voltage underground distribution line installed at a customer site and 15 m or less in length, indication of the buried object may be omitted. Intervals exceeding 10m are allowed in a place where no other person has access thereto or if that distribution line can be clearly located. (*1) Article 163 If it is installed at a customer site, indication of voltage alone is allowed. Underground Distribution Lines at Adjacency and Crossing with Other Objects If an underground distribution conductor approaches or crosses another underground buried object, a fireproof bulkhead shall be installed between the two if the approach is within the value shown in Table 163-1. Alternatively , the underground distribution conductor shall be installed in strong nonflammable or self-extinguishable noncombustible ductwork. If underground electrical conductors approach each other, the above-stated bulkhead or the like needs not be installed in case of the following paragraphs: 1. If each underground distribution conductor has a self-extinguishable noncombustible covering or are installed in a strong self-distinguishable noncombustible duct 2. If either underground distribution conductor has a nonflammable covering 3. If either underground distribution conductor is installed in a strong nonflammable duct 4. If a strong fireproof bulkhead is installed between the underground distribution conductors 5. If the approach takes place in an underground box Table 163-1 Clearance from underground distribution conductor to other buried objects Clearance Object Adjacent buried object Underground distribution conductor Low voltage Medium voltage Underground telecommunication line 30cm 60cm Pipe containing an inflammable or toxic 1m fluid (*1) Pipe other than a pipe containing an 30cm inflammable or toxic fluid (*2) Other underground Low voltage 15cm 30cm _________________________________________________________________________________________________________________________________________ Page 153 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) electrical lines Medium voltage High voltage 30cm 30cm 30cm (*1) A “Pipe containing an inflammable or toxic fluid” is not necessarily a gas pipe but it contains any liquid inflammable substance. A petroleum pipe, for example, belongs to this category. (*2) A “Pipe other than a pipe containing an inflammable or toxic fluid” includes a water supply pipe, steam pipe, district heating hot water pipe and the like which are nonflammable or covered with a nonflammable material. 3-6-6 Special Distribution Lines Article 164 1. Over water and Underwater Distribution Lines Over water distribution lines “Over water distribution lines” refer to such low-voltage distribution lines as installed over the water surface of a stream or the like. These shall be installed according to the following items: (1) Installation of over water distribution lines a. A cable of high wear resistance, shock resistance and bend resistance shall be used for the electrical conductor. b. Where the electrical conductors of an over water electrical line are to be connected to the electrical conductors of an overhead electrical line, they shall be installed so that no water gets inside the insulating covering of the electrical conductors from the connection point. The connection point of the electrical conductors shall be firmly attached to a supporting structure at a height equal to or greater than the value in Table 164-1. Table 164-1 Height of connection point of electrical conductor Place of connection Over the land (over the ground surface) Over the water point Over a road Not over a road Over the water surface Height Height of connection point 5m 4m 4m c. The distribution conductors of an over water electrical line shall be supported on a float and installed so as not to damage their covering. d. The float used for an over water electrical line shall be a series of floating objects firmly connected by a chain or the like. e. In an electrical circuit of an overhead distribution line used with an over water electrical line, a dedicated switching device and over current circuit breaker shall be installed for each pole. 2. Underwater distribution lines “Underwater distribution lines” refer to such low-voltage and medium-voltage distribution lines as installed on the bottom of a stream or the like. These shall be installed according to the following items: (1) Installation of underwater distribution lines a. The underwater power distribution line shall be installed at such a place where there is no danger of being damaged and in such a manner that it will incur no danger. _________________________________________________________________________________________________________________________________________ Page 154 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. Cable shall be used for the electrical conductor. c. The cable shall be put in a strong duct for installation. However, if the cable used for the electrical conductor is armored with galvanized iron wire with 6 mm in diameter or other metallic wire equal or superior thereto in its strength and thickness, it need not be put in a strong duct. Article 165 1. Distribution Lines over Bridge and Others Place and work type of installation Low- and medium-voltage distribution lines to be installed on a bridge or the like (*1) shall be installed by the work method shown in Table 165-1 according to Article 177. (*1) “Bridge or the like” includes railroad bridges, highway bridges and expressways. Table 165-1 Place and work method of installation Work Method Applicable work type Place Low-voltage Medium-voltage distribution line distribution line Insulator work, Cable work, Over a bridge or the like Synthetic resin tube work, Cable work Metallic tube work, Flexible duct work. Insulator work, Cable work, Side face of a bridge or the like Synthetic resin tube work, Cable work Metallic tube work, Bus duct work. Cable work, Synthetic resin tube work, Cable work Bottom face of a bridge or the like Metallic tube work, Flexible duct work. 2. Installation of low-voltage distribution lines (1) If low-voltage distribution lines are to be installed above a bridge or the like, the following shall be adhered to in installing the same and the height thereof shall be 5 m or more above the bridge road surface. a. An insulated conductor 3.0 kN or more in tensile strength shall be used for the electrical conductor. This shall be supported on cross arms firmly attached to building by using insulators of high insulating, nonflammable and water-proof capabilities. 3. (1) In this case, the clearance from an electrical conductor to the building parts shall be 30 cm or more. Installation of medium-voltage distribution lines If medium-voltage power distribution lines are to be installed over a bridge or the like, the following shall be adhered to in installing the same and the height thereof shall be 5.0 m or more above the bridge road surface. _________________________________________________________________________________________________________________________________________ Page 155 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) a. Cable shall be used for the electrical conductor. b. The cable shall be put in a strong duct or trough for installation. c. Earthing work Type A (*1) of Article 57-2 shall be done to the metallic part of the duct or other protective device in which the cable is laid down, the metallic wire connecting box, and the metallic body used for the cable sheath. Where an anticorrosive measure is taken to these metallic objects or the resistance to earth between these metallic objects and the ground is 10 or less (*2), earthing work Type A or Type D of Article 57-2 is not required to be done. (2) (*1) If they are installed so that there is no danger of a person touching it, earthing work Type D shall be done to the metallic body. (*2) If they are installed so that there is no danger of a person touching it, the resistance to earth shall be 100 or less. If they are installed on a side face or bottom face of a bridge or the like, the following shall be adhered to. a. Cable shall be used for the electrical conductor. b. The cable shall be put in a strong duct or trough or installed in such a manner that there is no fear of a person touching it. c. The cable supporting clearance shall be 2 m or less, and the cable shall be attached to the supports so as not to damage the cable covering. d. If the cable is to be suspended from a messenger wire for installation, the cable shall be installed so that it will not touch the building on which the distribution conductor is laid down. e. Earthing work Type A (*3) of Article 57-2 shall be given to the metallic part of the duct or other protective device in which the cable is laid down, the metallic wire connecting box, and the metallic body used for the cable covering. Where an anticorrosive measure is taken to these metallic objects or the resistance to earth between these metallic objects and the ground is 10 or less (*4), earthing work Type A or Type D of Article 57-2 is not required to be done. (3) (*3) If they are installed so that there is no danger of a person touching it, the metallic body shall be given earthing work Type D of Article 57-2. (*4) If they are installed so that there is no danger of a person touching it, the resistance to earth shall be 100 or less. Clearance to other facilities The clearance from the electrical conductors of a distribution line installed on a bridge or the like to another facility shall be equal to or greater than the value shown in Table 165-2. If it is installed with a strong fire-proof bulkhead installed in between, or the electrical conductors are laid down in a strong fire-proof duct or installation, a less value than that shown in Table 165-2 may be allowed. Table 165-2 Clearance from distribution line installed on a bridge or the like to another facility _________________________________________________________________________________________________________________________________________ Page 156 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Object Clearance Low-voltage distribution conductors, telecommunication conductors, water supply pipelines, gas pipelines or other similar objects installed on the same building 15 cm 3-7 Other cases (excluding another medium-voltage distribution line installed on the same building) 30 cm User’s Sites Electrical Installations 3-7-1 Indoor Installations Article 166 Restriction of Indoor Lines Voltage The line-to-earth voltage of an electric facility in a dwelling house shall be 300 V or less according to the safety measures mentioned in the following items: 1. In the case of TT earthing type, Earthing work Type D of Article 57-2 shall be given to any single-phase low-voltage equipment irrespective of the user’s site. 2. The indoor wiring shall contain protective earthing conductors beforehand to ensure the earthing of electric equipment. 3. A receptacle and plug with an earthing electrode shall be employed to make sure of earthing conductor connection between the receptacle and equipment’s plug. The receptacle and plug shall be of such shapes so as to prevent electric shock due to exposed live parts. Article 167 Restriction of Bare Conductors Bare conductor shall not be used for a low-voltage conductor to be installed indoors. However, this shall not apply if one of the following paragraphs is complied with. 1. If an electrical conductor named in the following items is used in an open place with insulator work according to Article 177. (1) Electrical conductor for use with electric furnaces (2) Electrical conductor to be installed in a place where the covering insulator of electrical conductor will corrode (3) Electrical conductor to be installed in a place prepared to block out any person other than the operator 2. If installed by bus duct work according to Article 177 3. If installed by lighting duct work according to Article 177 Article 168 Electrical Conductors Used for Indoor Wirings The low-voltage indoor wiring shall be annealed copper wire 1.6 mm in diameter or other wire equal or superior thereto in its strength and thickness. The above-stated thickness need not be adhered to if the operation voltage of the indoor wiring is 300 V or less and one of the following paragraphs is complied with. 1. Annealed copper wire 1.2 mm or more in diameter may be used for the wiring to neon lights, attendance indicator lamps or other similar devices or circuits. The same shall apply to the case where the wire is installed by synthetic resin tube work, metallic tube work, metallic raceway work, metallic duct work, floor duct work or cellular duct work. 2. Cable 0.75 mm2 or more in sectional area may be used for the wiring to neon lights, attendance indicator lamps or other similar devices or control circuits. The same shall apply to the case _________________________________________________________________________________________________________________________________________ Page 157 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) where a safety device is installed to automatically interrupt an overcurrent from the circuit if such occurs. 3. Cord (*1) 0.75 mm2 or over in sectional area may be used for the wiring to show windows or showcases. (*1) The term “cord” is referred to as a mobile electrical conductor to connect small electric equipment Article 169 Switching Devices at the Indoor Main Lines A switching device shall be installed on the low-voltage indoor circuit in a place near the service entrance and it shall be easy to open and close it. The above-stated switching device may be omitted on the following electrical circuit: 1. If the electrical circuit is an indoor circuit with an operation voltage of 300 V or less receiving electricity from a circuit 15 m or less in length that connects to another indoor circuit (*1). (*1) Article 170 “Another indoor circuit” refers only to a circuit that can be protected by an overcurrent circuit breaker with a rated current of 15 A or less or a distributing circuit breaker greater than 15 A up to 20 A. Indoor Wiring Utensils For the indoor electrical circuits to be installed in an ordinary home or factory, indoor wiring utensils attached to them shall be installed according to the following paragraphs: 1. The live parts shall not be exposed. The above shall not apply to a place prepared to block out any person other than the operator. 2. Low-voltage non-covered fuses shall be installed inside a box made of nonflammable material or a box lined with nonflammable material on all inner faces. 3. If they are installed in a humid or moist place, a dehumidifying device shall be installed. 4. If the wiring utensil is to be connected to an electrical conductor, the same shall be connected fast and electrically safely by screw fastening or the like. In addition, no tension shall act on the connection point. Article 171 Indoor Electrical Equipment and Appliances The term “indoor electrical equipment and appliances” refers to low-voltage incandescent lamps, discharge lamps, and household and business electric appliances installed indoors. These shall be installed according to the following paragraphs: 1. Incandescent or discharge lamps or household appliances shall be installed so that no live part is exposed. 2. Low-voltage business electrical appliances shall be installed so that the live parts are not exposed. The above shall, however, not apply to electric furnaces, electric welders, electric motors and other appliances that are used with some live part inevitably exposed and the case where these are installed in a place made inaccessible for any person other than the operator. 3. A household or business electric appliance with live parts accessible to persons shall not installed indoors. 4. If the indoor electric appliance is to be connected to an electrical conductor, the same shall be _________________________________________________________________________________________________________________________________________ Page 158 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) connected fast and electrically perfectly by means of screw fastening or the like. In addition, no tension shall act on the connection point. Article 172 Prevention of Obstacles Caused by High Frequency Current If the electric appliance has the possibility of generating radio waves or radio frequency currents that will continuously and seriously interfere with the function of radio, television or other wireless devices, it shall be installed according to the following paragraphs to prevent such interference. 1. For fluorescent lamps, a capacitor 0.006 F or more and 0.5 F or less (*1) in capacitance shall be provided in an appropriate place. (*1) If a fluorescent lamp is of the preheat start type and is connected in shunt with a glow lamp, the capacitance shall be 0.006 F or more and 0.01 F or less. 2. For a small AC series motor with an operation voltage in the low-voltage range and a rated output of 1 kW or less, one of the following shall be adhered to: (1) Capacitors 0.1 F and 0.003 F in capacitance shall be inserted respectively between motor terminals and between each motor terminal and the metallic case of the electric appliance using such small AC series motor or the frame of the small AC series motor or ground. (2) For an electric appliance containing a small AC series motor in such components that the frame of the motor is insulated from the appliance’s metallic case, steel stand and other accessible metallic parts, capacitors 0.1 F and capacitors more than 0.003 F in capacitance shall be inserted respectively between motor terminals and between each motor terminal and the motor frame or ground. (3) A capacitor 0.1 F in capacitance shall be inserted between each terminal and ground. (4) Capacitors 0.1 F and capacitors 0.003 F in capacitance shall be inserted respectively between electrical conductors that are connected to an electric appliance at a place close to that appliance and between each electrical conductor and the metallic case of the appliance or ground. 3. For a small AC series motor with an operation voltage in the low-voltage range and a rated output of 1 kW or less used for electric drills, a non-inductive capacitor 0.1 F in capacitance shall be inserted between motor terminals and a through-type capacitor with a capacitance of 0.003 F and sufficient shunting effect shall be inserted between each motor terminal and ground. 4. For a neon lamp flasher, an appropriate device shall be installed between power terminals and at a place close to each contact to prevent a radio-frequency current from occurring in the electrical circuit connected to the neon lamp flasher. Article 173 Over current Circuit Breakers for Electric Motors For an electric motor to be installed indoors with a rated output exceeding 0.2 kW, an appropriate device shall be installed to automatically block out, or alert the operator of an over current that may burn out the motor. This device is not required to be installed if one of the following paragraph is complied with. 1. If the motor is installed at such a position where the operator can normally monitor it while it is in operation. 2. If there is no danger of such an over current that may burn out the motor occurring in the motor winding, because of the structure or load Properties of the motor. If the electric motor is of the single-phase type and the rated current of an overcurrent circuit 3. _________________________________________________________________________________________________________________________________________ Page 159 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) breaker to be installed on its power supply side is 15 A or less (*1). (*1) Article 174 The rated current shall be 20 A or less for distributing circuit breakers. Installation of Mains for Electrical Circuits In installing the low-voltage indoor mains from the service entrance switch or the switchboard in the receiving room to the branching point of a branch circuit, the following paragraphs shall be complied with: 1. Installation of main conductors The mains shall be installed in a place free of danger of damage and an electrical conductor with an allowable current equal to or greater than the value given below shall be used for the mains. However, if the demand factor, load factor and the like are already known, an alternative electrical conductor with an allowable current equal to or greater than the value given below appropriately modified based on these factors may be used. (1) If the load on electric motors and the like is 50% or less: If the total of rated current of the electric motors and the like (*1) is not greater than the total of rated current of other household appliances, the allowable current shall be the total sum of rated current of the household appliances supplied from the mains. (*1) (2) “Electric motors and the like” includes electric motors and similar household appliances that require a large starting current. If the load on electric motors and the like exceeds 50%: The allowable current shall be the total of rated current of other household appliances to which the following value is added: 2. a. If the total of rated current of the motors and the like is 50 A or less, the allowable current shall be the value 1.25 times that total of rated current. b. If the total of rated current of the motors and the like exceeds 50 A, the allowable current shall be the value 1.1 times that total of rated current. Installation of over current circuit breakers On the power supply side of the mains, an over current circuit breaker to protect such mains shall be installed on each pole except the neutral wire according to the following items: (1) If motors and the like are not connected to the over current circuit breakers: (2) If motors and the like are connected to the over current circuit breakers: An over current circuit breaker having a rated current equal to or less than the value 3 times the total of rated current of the motors and the like to which the total of rated current of other household appliances is added shall be installed. However, it shall not exceed 2.5 times the allowable current of the mains. (3) Exceptions to installation of over current circuit breakers Installation of an over current circuit breaker may be omitted in the following cases: a. The case where the allowable current of the mains is 55% or more (*2) of the rated current of an over current circuit breaker that protects other mains connected to the power supply side of the mains concerned (*2) If the length of such mains is 8 m or less, the rated current shall be 35% or more. _________________________________________________________________________________________________________________________________________ Page 160 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. Article 175 The case of which length of mains is 3 m or less and to which no other mains are connected on the load side Installation of Branch Circuits A low-voltage indoor circuit branching off from low-voltage indoor mains and reaching household electric appliance shall be installed according to the following paragraphs: 1. Installation of switching devices and over current circuit breakers For a branch circuit, a switching device and over current circuit breaker shall be installed on each pole (*1) at a place within 3 m from the branching point on the mains. If the allowable current of the electrical conductor from the branching point to the switching device and over current circuit breaker is 55% or more (*2) of the rated current of the over current circuit breaker that protects the mains connecting to that electrical conductor, the switching device and over current circuit breaker may be installed at a place beyond 3 m from the branching point. 2. (*1) For the over current circuit breaker, the neutral pole is to be excluded. (*2) If the length of electrical conductor from the branching point to the switching device and over current circuit breaker is 8 m or less, it shall be 35% or more. Installation of branch circuits The branch circuits are divided into the following 3 classes according to the load types connected to them. (1) (2) Branch circuit supplying electricity to lamp load equipment with a rated current exceeding 50 A A branch circuit supplying electricity to one household electric appliance, other than a motor, with a rated current exceeding 50 A shall be installed as follows: a. No other load than this household electric appliance shall be connected to this branch circuit. b. The rated current of the over current circuit breaker shall not exceed the value 1.3 times the rated current of that household electric appliance (*3). (*3) If that value does not fit any standard rating of over current circuit breakers, employ the nearest larger rating. c. The allowable current of the electrical conductor shall be equal to or greater than the rated current of that household electric appliance and the over current circuit breaker according to b. above. Branch circuit supplying electricity to an electric motor alone A branch circuit supplying electricity to an electric motor alone shall be installed as follows: a. The rated current of the over current circuit breaker shall be 2.5 times the allowable current of the electrical conductor connecting to that over current circuit breaker (*4). (*4) If the rated current of that electrical conductor exceeds 100 A and the said rated current value does not fit any standard rating of over current circuit breakers, employ the nearest rating larger than that value. b. For each portion of the low-voltage indoor wiring, the allowable value of the electrical conductor of that portion shall be equal to or greater than the value 1.25 times (*5) the total of rated current of the electric motors supplied from that portion of the low-voltage indoor wiring. If the total of the rated current of the electric motors concerned exceeds 50 A, the (*5) _________________________________________________________________________________________________________________________________________ Page 161 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) allowable current shall be equal to or greater than 1.1 times that current. (3) Other branch circuits For branch circuits other than those described in Items (1) and (2) above, the capacity of the electrical conductor, receptacle, screw connector and socket connected to such branch circuit shall be as shown in Table 175-1 according to the magnitude of the rated current of the over current circuit breaker that protects the branch circuit. As to thickness of electrical conductor, annealed copper wire of the thickness shown in Table 175-1 or other wire of equal or larger rated current shall be used. Table 175-1 Installation of branch circuits Installation Type of low-voltage indoor circuit Circuit protected by an over current circuit breaker with a rated current of 15 A or less Circuit protected by an over current circuit breaker with a rated current of greater than 15 A and 20 A or less Thickness of electrical conductor in the portion (limited to 3 m or less) from a screw connector, socket or receptacle to its branching point Thickness of low-voltage indoor wiring Diameter 1.6 mm - Screw connector or socket to which to connect Receptacle with a rated current of 15 A or less Socket of the screw type with a nominal diameter of 39 mm or less, or a socket other than the screw type, or screw connector with a nominal diameter of 39 mm or less Socket for halogen lamps, or a socket for incandescent lamps other than halogen lamps or for mercury lamps, with a nominal diameter of 39 mm, or a screw connector with a nominal diameter of 39 mm Receptacle with a rated current of 20 A or less Circuit protected by an over current circuit breaker (excluding a distributing circuit breaker) with a rated current of greater than 15 A and 20 A or less Diameter 2 mm Circuit protected by an over current circuit breaker with a rated current of greater than 20 A and 30 A or less Diameter 2.6 mm Circuit protected by an over current circuit breaker with a rated current of greater than 30 A and 40 A or less Sectional area 8 mm2 Diameter 2 mm Circuit protected by an over current circuit breaker with a rated current of greater than 40 A and 50 A or less Sectional area 14 mm2 Diameter 2 mm Article 176 Receptacle to which to connect Diameter 1.6 mm Excluding a receptacle to which a plug with a rated current of less than 20 A can be connected Receptacle with a rated current of 20 A or over and 30 A or less Receptacle with a rated current of greater than 30 A and 40 A or less Receptacle with a rated current of greater than 40 A and 50 A or less Allowable Current of Indoor Wirings The allowable current of PVC-insulated conductor and XLPE-insulated conductor used for low-voltage indoor wiring shall conform to the following paragraphs: 1. Allowable current and current reduction factor of insulated conductor The allowable current of the conductors given in Table 176-1 is the value in this table multiplied by the allowable current correction factor (a) for ambient temperatures of 30C or less or by the _________________________________________________________________________________________________________________________________________ Page 162 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) current reduction factor calculated by the formula (b) ( denotes ambient temperature) of current reduction factor for ambient temperatures exceeding 30C according to the insulator materials given in Table 176-2. Table 176-1 Allowable current of indoor wiring Conductor Allowable current (A) Single wire (diameter, mm) Twisted conductor (nominal sectional area, mm2) 1.0 or more and less than 1.2 1.2 or more and less than 1.6 1.6 or more and less than 2.0 2.0 or more and less than 2.6 2.6 or more and less than 3.2 3.2 or more and less than 4.0 4.0 or more and less than 5.0 5.0 0.9 or more and less than 1.25 1.25 or more and less than 2 2 or more and less than 3.5 3.5 or more and less than 5.5 5.5 or more and less than 8 8 or more and less than 14 14 or more and less than 22 22 or more and less than 30 30 or more and less than 38 38 or more and less than 50 50 or more and less than 60 60 or more and less than 80 80 or more and less than 100 100 or more and less than 125 125 or more and less than 150 150 or more and less than 200 200 or more and less than 250 250 or more and less than 325 325 or more and less than 400 400 or more and less than 500 500 or more and less than 600 600 or more and less than 800 800 or more and less than 1000 1000 Annealed or hard-drawn copper wire 16 19 27 35 48 62 81 107 17 19 27 37 49 61 88 115 139 162 190 217 257 298 344 395 469 556 650 745 842 930 1,080 Hard-drawn aluminum wire 12 15 21 27 37 48 63 83 13 15 21 29 38 48 69 90 108 126 148 169 200 232 268 308 366 434 507 581 657 745 875 1,260 1,040 Aluminum alloy wire 12 14 19 25 35 45 58 77 12 14 19 27 35 44 63 83 100 117 137 156 185 215 248 284 338 400 468 536 606 690 820 980 Table 176-2 Current reduction factor 2. Insulator material Allowable current correction factor (a) Formula (b) of current reduction factor PVC (excluding heat-resistant polymers) 1.00 60 30 XLPE (limited to cross-linked polymers) 1.41 90 30 Allowable current when put in a conduit If the insulated conductors in Paragraph 1 are placed in a synthetic resin raceway, synthetic resin tube, metallic raceway, metallic tube or flexible conduit for use, the allowable current of that conductor shall be the allowable current prescribed in Paragraph 1 multiplied by the current _________________________________________________________________________________________________________________________________________ Page 163 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) reduction factor (c) in Table 176-3. Table 176-3 Current reduction factor when put in conduit Number of electrical conductors in one conduit 3 or less 4 5 or 6 7 or over and 15 or less 16 or over and 40 or less 41 or over and 60 or less 61 or over Article 177 1. Current reduction factor (c) 0.70 0.63 0.56 0.49 0.43 0.39 0.34 Indoor Wiring Works Work methods and their applications The work methods of low-voltage indoor wiring include the 13 types given in the following items, i.e., synthetic resin tube work, metallic tube work, flexible conduit work, cable work, insulator work, synthetic resin raceway work, metallic raceway work, metallic duct work, bus duct work, floor duct work, cellular duct work, lighting duct work and flat protective layer work, and they shall be applied according to the division of places of installation and operation voltages as shown in Table 177-1. Table 177-1 Application of low-voltage indoor wiring work Operation voltage Place of installation Kind of work Synthetic resin tube work Metallic tube work 300 V or less Greater than 300 V Accessible Inaccessible Accessible Inaccessible Open place concealed concealed Open place concealed concealed place place place place Dry Other Dry Other Dry Other Dry Other Dry Other Dry Other place places place places place places place places place places place places ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Flexible conduit work Cable work ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Insulator work ○ ○ ○ ○ ○ ○ ○ ○ Synthetic resin raceway work Metallic raceway work Metallic duct work ○ ○ ○ ○ ○ ○ ○ ○ Bus duct work ○ ○ ○ ○ ○ Floor duct work ○ Cellular duct work ○ Lighting duct work ○ ○ Flat protective layer work ○ The mark ○ : indicates a place where the work concerned can be executed. (1) Synthetic resin tube work _________________________________________________________________________________________________________________________________________ Page 164 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Synthetic resin tube work is executed by drawing the insulated conductor into a synthetic resin tube that mainly uses hard vinyl conduit or flexible synthetic resin conduit. It is less expensive and easier in execution than the execution of metallic tube work, and good at insulating properties and excellent in chemical resistance. It is, however, weaker to mechanical impact and heat than metallic tubes. Therefore, the said work shall be executed in such a manner so that the pressure of heavy objects or severe mechanical impact can be avoided. (2) Metallic tube work Metallic tube work is executed by drawing the insulated conductor into a steel conduit. This work method is strong against the mechanical impact and, widely used for installation of low-voltage wiring in an office building or factory. (3) Flexible conduit work Flexible conduit work is executed by drawing the insulated conductor into a flexible conduit. This work method may be employed for the connection of wiring to vibrating equipment or the joints between structures or other points or places where some positional slippage is foreseeable, or where complex bent may exist. (4) Cable work This work uses PVC cable or polyethylene cable for the electrical conductor. This cable can be directly attached to a building and can be used for wiring in a limited installation space. (5) Insulator work This insulator work is executed by supporting the electrical conductor with insulators. This work method is economical and relatively easy to execute. It can be used for wiring in a place where an ample installation space can be secured. (6) Synthetic resin raceway work A kind of exposed wiring is employed where prefabricated building. In executing interior synthetic resin raceway is often attached to baseboard, and insulated conductor can be raceway lid. (7) buried wiring is difficult, such as, in a concrete finishing of a dwelling house, for example, a the ceiling molding, ceiling cross members or put in the raceway afterward by removing the Metallic raceway work Wiring is installed by laying insulated conductor in a metallic raceway. This work method can be used for indoor wiring where little importance is put on the aesthetics or at the drop section of a switch or receptacle when the switch or receptacle position is changed due to a design change in concrete building. (8) Metallic duct work This metallic duct work is executed by laying many electrical conductors in a bundle in a duct made of iron plate. This work method is more economical and gives a better appearance than that of metallic tube work. Additions and changes to the wiring are relatively easy. Therefore, it can be used for wiring in and around the power receiving and transformer room of a factory or office building. (9) Bus duct work A bus duct is a wiring material consisting of a conductor strip laid in a metallic duct called a housing (also called an enclosure) and has the following features: a. Capacity of electrical conductor can be large. _________________________________________________________________________________________________________________________________________ Page 165 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) b. Highly reliable because the supporting insulator hardly deteriorates. b. Easy to maintain because of simple wiring. d. Easy to execute. It can be used for the large-capacity mains in a factory or the like. (10) Floor duct work Wiring is made by embedding a metallic duct with a wiring take-off in a dry concrete floor of an office building or the like. For any equipment placement in a large room, a power line or signal line can be taken out from the floor surface near the equipment for connection. It can be used in the case where many persons are using telephones or business machines on desks, where the type and layout of equipment are not determined at the time of construction, and where equipment is added or the room is rearranged frequently. (11) Cellular duct work Corrugated deck plates are generally used as a form of floor concrete or floor members of a large steel building. In this method, the corrugation furrows are closed and used as cellular ducts. It can be used in combination with metallic duct, floor duct or metallic tube work. (12) Lighting duct work Conductors are laid down in the duct, and appliance attachment plugs are installed at arbitrary positions in the duct. Lighting appliances and other small appliances are attached to these. Because the appliance attachments can be arbitrarily shifted, this method can be used in a shop or department store where rearrangement takes place frequently, an office building where change of room partitioning is frequent, or in a factory where small appliances are used in a large number. (13) Flat protective layer work An electrical conductor made of a flat conductor and synthetic resin insulator and covered with a flat protective layer can be used on the floor surface of an office building or the like. It shall not be installed in a dwelling house, lodging rooms of an inn or the like, class rooms of a kindergarten or elementary or junior high school, sickrooms of a hospital or the like, or at a floor surface fitted with a heating element for floor heating. 2. Execution methods of various types of work The execution methods of the various types of work in Paragraph 1 shall conform to Table 177-2. Table 177-2 Electrical conductors, earthing work and installation methods of low-voltage indoor wiring Kind of Work Synthetic resin tube work Metallic tube work Electrical conductor Insulated and stranded wire (excluding the case of 3.2 mm or less) Insulated and stranded wire (excluding the case of 3.2 mm or less) Earthing work Earthing work Type D shall be applied to tubes for 300 V or less and Type C for more than 300 V (*2) Installation method Connection of electrical conductors is not allowed in the tube Tube supporting clearance shall be 1.5 m or less Connection of electrical conductors is not allowed in the tube Tube and accessories shall be made of brass or copper Tube wall thickness shall be 1.2 mm or over for embedment in concrete and 1 mm or over for _________________________________________________________________________________________________________________________________________ Page 166 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Flexible conduit work Cable work Insulator work Insulated and stranded wire (excluding the case of 3.2 mm or less) Cable Earthing work Type D shall be applied to tubes for 300 V or less and Type C for more than 300 V (*2) Earthing work Type D shall be applied to the metallic parts of protective devices that accommodate electrical conductors for 300 V or less, and Type C for more than 300 V. Insulated conductor (excluding PVC-insulated conductor) (*1) - Synthetic resin raceway work Metallic raceway work Metallic duct work Insulated conductor (excluding PVC-insulated conductor) Insulated conductor (excluding PVC-insulated conductor) Insulated conductor Bus duct work Bus duct Floor duct work Insulated and stranded wire (excluding the case of 3.2 mm or less) Cellular duct work Insulated and stranded wire (excluding the case of 3.2 mm or less) Lighting duct Lighting duct work others Connection of electrical conductors is not allowed in the tube Tube and accessories shall be made of metal Wire supporting clearance shall be 2 m or less (if laid down along the bottom or side of a building part) and 6 m or less (if laid down vertically in an inaccessible place) Provide an appropriate protective device for electrical conductor installed in a place subject to the pressure of heavy objects or severe mechanical impact. Exclude easy access for 300 V or less. Exclude access for more than 300 V. Clearance of electrical conductors is 6 cm or over Clearance from electrical conductor to building part shall be 2.5 cm or over for 300 V or less and 4.5 cm or over for more than 300 V (2.5 cm or over in a dry place). Supporting clearance shall be 2 m or less (for wire laid down along the top or a side of a building part). 6 m or less, however, for voltages exceeding 300 V and electrical conductor laid down otherwise. Connection of electrical conductors is not allowed in the raceway Earthing work Type D shall be applied to the raceway. Connection of electrical conductors is not allowed in the tube Tube and accessories shall be made of brass or copper Earthing work Type D shall be applied to ducts for 300 V or less and Type C for more than 300 V. Connection of electrical conductors is not allowed in the duct The sum of the sectional area of wires laid down in a duct shall be 20% or less of the inner sectional area of the duct Duct shall be more than 5 cm in width and 1.2 mm or over in wall thickness made of iron plate galvanized or coated with enamel or the like Duct supporting clearance shall be 3 m or less Duct supporting clearance shall be 3 m or less if attached to a building part In a humid place, use a duct for outdoor use and see that no water collects inside. Earthing work Type D shall be applied to ducts for 300 V or less and Type C for more than 300 V (*2). Earthing work Type D shall be applied to the duct. Earthing work Type D shall be applied to the duct. Earthing work Type D shall be applied to the duct (excluding ducts 4 m Connection of electrical conductors is not allowed in the duct (wire branching is excluded if that branch is easily accessible.) Duct shall be 2 mm or over in wall thickness made of steel plate galvanized or coated with enamel or the like Connection of electrical conductors is not allowed in the duct (wire branching is excluded if that branch is easily accessible.) Duct supporting clearance shall be 2 m or less Do not install a duct through a building part. _________________________________________________________________________________________________________________________________________ Page 167 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Flat protective layer work or less in length). Earthing work Type D shall be applied to the upper protective layer, upper installed protective layer, joint box, and metallic case of an insertion connector. Used on a branch circuit protected by an overcurrent circuit breaker of 30 A or less Line-to-earth voltage of the circuit shall be 300 V or less Install a leakage circuit breaker on the power supply circuit. (*1) Use bare conductor if Article 167-1-(1), (2) or (3) is complied with. (*2) Apply earthing work Type D of Article 57-2 if 300 V is exceeded and there is no danger of a person’s touching the duct. Article 178 1. Flat conductor-syntheti c resin insulated conductor Indoor Wirings for Adjacency and Crossing Insulator work If low-voltage indoor wiring is to be installed by insulator work, the clearance from the low-voltage indoor wiring to a telecommunication conductor, water supply pipe, gas pipe or other similar object shall be 10 cm or more (*1). (*1) 2. If the conductor is bare wire, the clearance shall be 30 cm or more. Work other than insulator work If low-voltage indoor wiring is to be installed by synthetic resin raceway work, synthetic resin tube work, metallic tube work, metallic raceway work, flexible conduit work, metallic duct work, bus duct work, floor duct work, cellular duct work, lighting duct work, flat protective layer work or cable work, it shall be installed in such a manner so as not to contact a telecommunication conductor, water supply pipe, gas pipe or other similar object. 3. Conditions where low-voltage indoor wiring and a telecommunication conductor may be laid down in the same tube, box or the like It is prohibited that low-voltage indoor wiring is installed together with a telecommunication conductor, as it is quite likely that there is a danger of erroneous contact. As an exception, however, such installation is allowed if the necessary safety measures mentioned below are taken. (1) (2) (3) If the low-voltage indoor wiring is to be installed by synthetic resin work, metallic tube work, metallic raceway work or flexible conduit work with its electrical conductor laid down in a separate tube or raceway from the telecommunication conductor, the installation shall take place by placing a strong bulkhead between the electrical conductor and telecommunication conductor and laying down the electrical conductors and telecommunication conductor in a duct or box whose metallic part is given earthing work Type C of Article 57-2. If the low-voltage indoor wiring is to be installed by metallic duct work, floor duct work or cellular duct work, the same shall be installed by placing a strong bulkhead between the electrical conductors and telecommunication conductor and by laying down the electrical conductors and telecommunication conductor in a duct or box whose metallic part is given in the earthing work Type C of Article 57-2. If the low-voltage indoor wiring is to be installed by a work method other than bus duct work, such a telecommunication conductor for a control circuit or the like and a telecommunication conductor equal or superior to the insulated conductor in its insulating effect shall be used for the telecommunication conductor. Article 179 1. Indoor Installations for Electric Lamps An electric lamp wire (*1) with an operation voltage of 300 V or less installed indoors shall be a cord other than a vinyl-insulated cord and its sectional area shall be 0.75 mm2 or more. _________________________________________________________________________________________________________________________________________ Page 168 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) However, for electric lamp wires installed so as to exclude the danger of a person touching them and at a height of 1.8 m or more, PVC-insulated conductor may be used if the wires attached to the lamp base have a wire spacing of 10 mm or more at the lead portion and use annealed copper wire with a sectional area of 0.75 mm2 or more. (*1) “Electric lamp wire” refers to an electrical conductor used for supplying electricity to an incandescent lamp suspended by it from a ceiling or the like at a user’s site and not fixed on a building. 2. For the connection of a low-voltage electric lamp wire with an operation voltage of 300 V or less installed indoors to the indoor wiring, the weight of the electric lamp or other devices shall not be borne by the indoor wiring at the connection point. 3. No electric lamp wire with an operation voltage exceeding 300 V shall be installed indoors. Article 180 Mobile Electrical Wirings Low-voltage mobile electric wires shall be those described in the following paragraphs: 1. General case: For a mobile electrical conductor with an operation voltage of 300 V or less installed indoors, a cord other than a vinyl-insulated cord and with a cross-sectional area of 0.75 mm2 or more shall be used. 2. If a vinyl-insulated cord is to be used: For a mobile electrical conductor with an operation voltage of 300 V or less attached to an electric heater (*1) or mobile flasher, a vinyl-insulated cord with a sectional area of 0.75 mm2 or more may be used. (*1) 3. “Electric heater” includes discharge lamps, electric fans, desk lamps and other electricity-consuming devices directly connected to a supply circuit, not through an insertion connector even if these do not use electric energy for heat as well as electric foot warmers and other devices having such a structure that the hot part is not exposed and there is no danger of an electrical conductor touching the hot part. If a tinsel cord is to be used: A tinsel cord (*2) has an allowable current of only about 0.5 A. It is not desirable for safety reasons to use such cord, as it will not be always protected without fail by the over current circuit breaker on the branch circuit. However, for electric shavers, electric hair clippers or other similar light and small household electric devices that are used with quick movement, an ordinary cord does not have sufficient flexibility and suffers broken strands frequently. Therefore, use of a tinsel cord of high flexibility is required. A tinsel cord 2.5 m or less in length may be used for the mobile electrical conductor attached to an electric shaver, electric hair clippers or other similar light and small household electric devices only if these are used in a dry place. (*2) “Tinsel cord” refers to a highly flexible cord of 18 copper wires with a sectional area of 0.074 mm2 or less and 0.009 mm2 or more, each wound on a twined thread at a uniform rate of 16 turns per 10 mm, and then stranded into the core of the cord. 4. Connection of mobile electrical conductors (1) Connection to wiring For the connection of a mobile electrical conductor to low-voltage indoor wiring, an insertion _________________________________________________________________________________________________________________________________________ Page 169 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) connector or other similar device shall be used. (2) Connection to electricity-consuming device For the connection of a mobile electrical conductor to an electricity-consuming device, an insertion connector or other similar device shall be used. However, these devices need not be used if the cord is fixed by screws to terminal hardware installed so as to exclude the danger of a person touching it easily. (3) Connection to earthing conductor If an earthing conductor is to be laid down to the metallic case of an electricity-consuming device connected to a low-voltage mobile electrical conductor laid down indoors, one of the core conductors of that mobile electrical conductor may be used for the earthing conductor. For the connection of that core conductor to the earthing conductor fixed to the case of the electricity-consuming device and a building part, one pole of the insertion connector or other similar device used for the connection of the mobile electrical conductor to the electricity-consuming device or indoor, exterior wall or indoor wiring shall be used. However, if the mobile electrical conductor is connected by screws to the electricity-consuming device, this provision is not necessarily adhered to for the connection to the electricity-consuming device. This insertion connector or other similar device shall have such a structure that the pole connected to the earthing conductor can be definitely distinguished from the other pole. 3-7-2 Outdoor Installations Article 181 1. Outdoor Installations Installation of hanger wires for outdoor lamps For a hanger wire of an outdoor incandescent lamp, an insulated conductor equal or superior in strength and thickness to an annealed copper wire 1.6 mm in diameter shall be used for the electrical conductor in the section up to a height of less than 2.5 m above the ground surface, and shall be installed so as to prevent the contact of persons or wire damage if it is installed in a place where there is a fear of a person touching it easily. This shall not apply if it is installed by cable work according to Article 177. 2. Installation of exterior wall or outdoor wiring (1) Work methods and their applications The work methods for outdoor or exterior wall wiring include the following 6 types: synthetic resin tube work, metallic tube work, flexible conduit work, cable work, insulator work and bus duct work according to Article 177. These shall be applied in conformity with Table 181-1 according to the division of installed places and operation voltages. Table 181-1 Applications of low-voltage outdoor and exterior wall wiring work Operation voltage 300 V or less More than 300 V _________________________________________________________________________________________________________________________________________ Page 170 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Installed place Kind of Work Synthetic resin tube work Open place Accessible concealed place Other places Open place Accessibl e concealed place Other places ○ ○ ○ ○ ○ ○ Metallic tube work ○ ○ ○ ○ ○ ○ Flexible conduit work ○ ○ ○ ○ ○ ○ Cable work ○ ○ ○ ○ ○ ○ Insulator work ○ ○ ○ Bus duct work ○ ○ ○ ○ The mark ○ indicates a place where the work concerned can be executed. (2) Execution methods of the various types of work For the execution method of work, Article 177-2 shall apply with necessary modifications. For the duct of bus duct work, a bus duct for outdoor use shall be used and no water shall permeate inside. Any equipment and/or facilities of which operation voltage exceeds 300 V shall be installed in such a manner so as to allow nobody to easily enter or touch the buildings other than a wooden building. (3) Installation of switching devices and over current circuit breakers Switching devices and over current circuit breakers of low-voltage outdoor or exterior wall wiring shall not serve as those for indoor circuits. However, if the length of the wiring concerned is 8 m or less from the branch of the indoor circuit and the rated current of the over current circuit breaker for the indoor circuit is 15 A or less (*1), they may serve for both. (*1) For a distributing circuit breaker, the rated current shall be 20 A or less. 3. Installation of electric lamp wires installed on exterior walls or outdoors 4. An electric lamp wire installed on an exterior wall or outdoors shall be installed according to Article 179. Installation of mobile electrical conductors installed on exterior walls or outdoors A mobile electrical conductor installed on an exterior wall or outdoors shall be installed according to Article 180. If a mobile electrical conductor is connected to an exterior wall or outdoor wiring, an insertion connector shall be used. 5. Installation of wiring devices or the like to be installed on exterior walls or outdoors Wiring devices and electrical equipment and devices to be installed outdoors shall be installed according to the following items: (1) For wiring devices and wiring within an electrical equipment and device, parts where there is a fear of a person touching it or a danger of such part being damaged shall be installed by metallic tube work or cable work (*1) according to Article 177. (*1) (2) Limited to cable work by which the electrical conductor is laid down in a metallic tube or other protective device For wiring devices, switching devices, connectors, flashers and other devices installed in an electrical equipment and device, a strong protective device shall be provided if there is a danger of these devices being damaged. 3-7-3 Special Installations _________________________________________________________________________________________________________________________________________ Page 171 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) Article 182 Traffic Signals The electrical circuit from the control device of a traffic sign or the like to be installed at an intersection or the like to the electric lamp of the traffic sign or the like shall be installed according to the following paragraphs: 1. The wiring to a traffic sign lamp shall be installed according to the following items: (1) The electrical conductor shall be of a PVC-insulated conductor equal or superior in strength and thickness to an annealed copper wire 1.6 mm in diameter unless it is cable. (2) If the electrical conductor is a PVC-insulated conductor, it shall be suspended from a metallic wire with a tensile strength of 5 kN or two or more stranded iron wires of 4 mm in diameter or more. (3) For the metallic wire of Item (2) for electrical conductor suspension, an insulator shall be inserted at or near the supporting structures. 2. The hanger wire of a traffic sign lamp shall be installed according to the following items: (1) The height of the electrical conductor shall be 2.5 m or more above the ground surface. (2) If the electrical conductor is to be installed by insulator work, the electrical conductor shall be bundled at appropriate intervals. 3. On the power supply side of the control device of a traffic signal lamp, a dedicated switching device and over current circuit breaker shall be installed on each pole. 4. To the metallic case of the control device of a traffic signal lamp, earthing work Type D of Article 57-2 shall be applied. 5. If the wiring of a traffic signal lamp circuit approaches or crosses a facility other than a building, road, pedestrian overpass, railroad, overhead telecommunication conductor, antenna or overhead electrical conductor, the clearance from the wiring of the traffic signal lamp circuit to such object shall be 60 cm or more (*1). (*1) Article 183 If the wiring of the traffic sign lamp is a cable, the clearance shall be 30 cm or more. Public Streetlamps If an incandescent lamp, fluorescent lamp, mercury lamp or the like with a line-to-earth voltage of 300 V or less is to be installed on a supporting structure of a power distribution line, it shall be installed according to the following paragraphs: 1. Approval for installation of a public streetlamp If a public streetlamp is to be installed on a supporting structure owned by a power utility company, approval shall be obtained from the owner. 2. Lighting apparatus of public streetlamps (1) The apparatus shall not be fitted with accessories for a shop’s signboard or ornamental purposes. The apparatus shall be strong and durable and shall be attached to a pole firmly. (2) (3) The apparatus in its installed state shall incur no troubles even if subjected to slanted rainfall up to 45 degrees from the vertical direction. (4) The apparatus shall have a structure that allows for easy replacement of the bulbs and the like. (5) The lead wire of the apparatus shall have a conductor with a sectional area of 0.75 mm2 or over. _________________________________________________________________________________________________________________________________________ Page 172 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) (6) The apparatus attaching band and attaching accessory hardware shall be made of steel plate given an anticorrosive treatment of galvanizing or stainless steel, which allows for easy attachment and detachment. (7) The weight shall be 100 kg or less including the accessories. 3. Installation of apparatus (1) The attaching height of the apparatus shall be 4.5 m or over from the ground surface to the apparatus bottom. However, it shall be 3.0 m or over above the ground surface if this height does not hinder traffic. (2) For an incandescent or fluorescent lamp, the horizontal jutting distance shall be within 1 m from the point of attachment of the apparatus to the pole. 4. Installation of lamp lighters (1) Automatic lamp lighters of the photoelectric type not built in the apparatus shall be installed at a place where it is not influenced by ambient light. (2) Manual lamp lighters shall have a structure that prevents permeation of rainwater or the like according to the installed place and shall be installed at a place where there is little danger of being damaged and where operations are easy. 5. Wiring The wiring shall use, for the electrical conductor, an insulated conductor of 1.6 mm or more or other wire equal or superior to the above insulated conductor in its insulating effect and shall be installed according to one of the work methods in the following items: (1) Cable wiring according to Article 177 (2) Synthetic resin tube wiring according to Article 177 (3) Metallic tube wiring according to Article 177 Article 184 Submarine Lamps An underwater floodlight for use in a swimming pool or other similar floodlight shall be installed according to the following paragraphs: 1. The floodlight shall be put in a container conforming to the following items and shall be fitted with an appropriate protective device if it is installed in a place where there is a danger of being damaged. (1) The radiating window shall be made of glass or lens and the other parts shall be made of a strong metal given an anticorrosion treatment with a non-corrosive metal, cadmium plating, galvanizing, painting or the like. (2) An earth terminal shall be installed at an appropriate internal place. In this case, the earth terminal screw shall be of 4 mm or more in diameter. (3) For the floodlight, its screw connectors and sockets shall be made of porcelain except for the socket for fluorescent lamps. (4) The floodlight in its finished state shall undergo a dielectric strength test by impressing an alternating voltage of 2,000 V between a conducting part and a part other than the conducting parts for 1 continuous minute and shall endure that test voltage. (5) The floodlight in its finished state shall be fitted with an electric lamp of the wattage of its _________________________________________________________________________________________________________________________________________ Page 173 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) maximum optimum lamp and immersed in water to a depth of 15 cm or more if its rated maximum depth is 15 cm or less (*1). Supply electricity to it at the voltage equivalent to the rated voltage of that lamp for 30 minutes and suspend the supply of electricity for 30 minutes. Repeat this cycle of operations 6 times. There shall be nothing wrong in the floodlight such as water getting in the container. (*1) If the rated maximum depth exceeds 15 cm, the immersion depth shall be that rated maximum depth or more. (6) The wattage of the maximum applicable lamp and the rated maximum depth shall be indicated at a place easy to see. 2. For supply of electricity to the floodlight, an insulating transformer with operation voltages of 600 V or less and 300 V or less in the primary and secondary circuits respectively shall be used. 3. The insulating transformer in Paragraph 2 shall be installed according to the following items: (1) The secondary circuit of the insulating transformer shall not be earthed. (2) If the operation voltage of the secondary circuit is 30 V or less, the insulating transformer shall be fitted with a metallic plate between the primary and secondary windings to prevent an erroneous contact and the metallic plate shall be given earthing work Type A of Article 57-2. In this case, the earthing conductor shall be of PVC-insulated conductor or cable if the earthing conductor used for earthing work Type A is to be installed in a place where there is the danger of a person touching it. 4. The insulating transformer in Paragraph 2 shall undergo a dielectric strength test by impressing an alternating test voltage of 5,000 V between one winding and another winding, the iron core, and the case for one continuous minute and shall endure that test voltage. 5. The secondary circuit of the insulating transformer in Paragraph 2 shall be fitted with a switching device and over current circuit breaker on each pole. 6. If the operation voltage of the secondary circuit of the insulating transformer in Paragraph 2 exceeds 30 V, an appropriate device shall be installed to automatically interrupt the circuit if an earth fault occurs in that circuit. 7. The switching device or over current circuit breaker in Paragraph 5 or the device in Paragraph 6 to automatically interrupt the circuit if an earth fault occurs shall be put in a strong metallic case, which shall be given earthing work Type C in Article 57-2. 8. The secondary wiring of the insulating transformer in Paragraph 2 shall be installed by metallic tube work. 9. For the mobile electrical conductor to supply electricity to the floodlight in Paragraph 1, a continuous length of cable with no connection point having a sectional area of 2 mm2 or over shall be used, and if it is to be installed at a place where there is the danger of its being damaged, an appropriate device shall be installed. For the connection of the mobile electrical conductor in Paragraph 9 to the wiring in Paragraph 8, an insertion connector shall be used. It shall be put in a metallic case having a structure to prevent water penetration, which shall be installed at a place other than underwater or other similar places. 11. To the metallic part of the container and protective device in Paragraph 1, earthing work Type C in Article 57-2 shall be applied. In this case, one of the core conductors of the mobile electrical conductor in Paragraph 9 shall be used as the earthing conductor, and for the connection of this earthing conductor to the earthing conductor attached to the metallic part of the container in Paragraph 1 and its case and the building, one pole of the insertion connector in Paragraph 10 shall be used. _________________________________________________________________________________________________________________________________________ Page 174 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA) 12. The metallic part of the container in Paragraph 1, the metallic part of the protective devices in Paragraphs 1 and 9, the metallic cases in Paragraphs 7, 10 and 11, the metallic tube used for the wiring in Paragraph 8, and the earthing conductor in Paragraph 11 shall all be connected to one pole of the insertion connector, and these connections shall be mutually electrically perfect. 13. An underground floodlight for use in a swimming pool need not conform to the provisions of Paragraphs 1 to 12 if it is installed according to IEC 60364-7-702 (1997-11) [Electrical Installations of buildings – Part 7: Requirements for special installations or locations – Section 702: Swimming pools and other basins]. _________________________________________________________________________________________________________________________________________ Page 175 of 175 Lao Electric Power Technical Standard. First Edition in the year 2004/ Ministry of Industry and Handicrafts/ Department of Electricity Supported by Japan International Cooperation Agency(JICA)
