PROFESSIONAL TRAINING REPORT
SUBMITTED TO
THE COUNCIL OF REGISTERED
PROFESSIONAL ENGINEERS OF
MAURITIUS
FOR REGISTRATION IN THE FIELD OF
ELECTRICAL & ELECTRONIC
ENGINEERING
THROUGH TRAINING UNDERGONE
AT
CENTRAL ELECTRICITY BOARD
MAURITIUS
SATYAM DOOKHITRAM
APRIL 2019
Table of Contents
TABLE OF CONTENTS
LIST OF FIGURES .................................................................................................. 6
LIST OF TABLES..................................................................................................... 8
ACKNOWLEDGEMENT .......................................................................................... 9
APPLICANT'S DECLARATION ............................................................................. 10
SUPERVISOR'S DECLARATION .......................................................................... 11
LIST OF ABBREVIATIONS ................................................................................... 12
CHAPTER 1: BACKGROUND ............................................................................... 13
1.1 Introduction ................................................................................................... 14
1.2 Time Utilisation ............................................................................................. 15
CHAPTER 2: TRAINING ENVIRONMENT ............................................................ 16
2.1 Introduction ................................................................................................... 17
2.2 Overview of the Central Electricity Board ..................................................... 17
2.3 The Transmission and Distribution (T&D) department .................................. 18
2.3.1 Engineering (District) Section ................................................................. 19
2.3.2 General Planning Section ....................................................................... 20
2.3.3 Technology and Procurement (T&P) Section ......................................... 22
2.3.4 System Control Section ......................................................................... 23
2.3.5 Construction & Maintenance (C&M) Section .......................................... 24
2.3.6 Project and Construction (P&C) Section ................................................. 26
2.4 The Production department (CMG)............................................................... 27
CHAPTER 3: NATURE OF TRAINING .................................................................. 29
3.1 The Engineering (District) Section ................................................................ 30
3.1.1 Introduction: The Distribution Process .................................................... 30
3.1.2 The Distribution System ......................................................................... 31
3.1.3 Primary and Secondary Distribution ....................................................... 31
2
Table of Contents
3.1.4 The Overhead System............................................................................ 32
3.1.5 Main components of overhead lines ....................................................... 33
3.1.6 Overhead line clearances with respect to structures .............................. 37
3.1.7 Underground Network ............................................................................ 37
3.1.8 Health and Safety ................................................................................... 40
3.2 The Project and Construction (P&C) Section ................................................ 42
3.2.1 Introduction ............................................................................................. 42
3.2.2 The Transmission Network ..................................................................... 42
3.2.3 Overhead line transmission .................................................................... 42
3.2.4 Project Management in implementing 66kV overhead transmission line 49
3.2.5 The Underground Transmission network ................................................ 51
3.3 Technology and Procurement (T&P) Section ............................................... 53
3.3.1 Introduction: ............................................................................................ 53
3.3.2 The Store Ordering Committee .............................................................. 53
3.3.3 Launching of Tenders or Quotations ...................................................... 54
3.3.4 Steps involved in the analysis of Quotations .......................................... 54
3.3.4.1 Quotation Procedure ........................................................................ 54
3.3.4.2 Evaluation stage of quotation ........................................................... 54
3.3.5 Request for inspection ............................................................................ 55
3.4 System Control Section ................................................................................ 56
3.4.1 Introduction ............................................................................................. 56
3.4.2 The Daily Load Curve ............................................................................. 56
3.4.3 Frequency Control .................................................................................. 57
3.4.4 Voltage Control ....................................................................................... 58
3.4.5 Spinning Reserve ................................................................................... 58
3.4.6 Automatic Load Shedding ...................................................................... 59
3.5 General Planning Section ............................................................................. 60
3.5.1 Introduction ............................................................................................. 60
3.5.2 The Planning Procedures ....................................................................... 60
3.6 The Construction and Maintenance (C&M) Section ...................................... 62
3.6.1 Introduction ............................................................................................. 62
3
Table of Contents
3.6.2 The distribution transformer .................................................................... 62
3.6.3 Main components of the distribution transformer .................................... 63
3.6.4 Power transformer .................................................................................. 65
3.6.5 Tests performed on distribution transformers ......................................... 65
3.6.6 The 66/22 kV substation ......................................................................... 67
3.7 Construction and Maintenance Gang (CMG)- Production Department ......... 71
3.7.1 Introduction ............................................................................................. 71
3.7.2 Project Background of St Louis power station ........................................ 71
3.7.3 Power Generation of St Louis power station .......................................... 71
3.7.4 The Wartsila 18V46 diesel engine .......................................................... 72
3.7.5 Excitation System ................................................................................... 73
3.7.6 The synchronous generator .................................................................... 74
3.7.7 The Governor ......................................................................................... 75
3.7.8 The Automatic Voltage Regulator ........................................................... 75
3.7.9 The Differential Amplifier ........................................................................ 77
CHAPTER 4: PERSONAL CONTRIBUTION ......................................................... 80
4.1 Introduction ................................................................................................... 81
4.2 Wind loading calculation on 14m concrete pole ............................................ 81
4.3 Evaluation of quotation for bimetallic lug ...................................................... 88
4.3.1 Use of bimetallic lug ............................................................................... 88
4.3.2 Requirements sent to bidders by CEB.................................................... 88
4.3.3 The Evaluation Process.......................................................................... 89
4.4 Supply to 41 housing units for NHDC morcellement at 16ème mille............. 91
4.4.1 The design process ................................................................................ 91
4.4.2 Cost Estimate ......................................................................................... 99
4.5 Load test and load balancing ........................................................................ 99
4.5.1 Load balancing at Montagne Blanche village ....................................... 100
4.6 Earth Resistance Test ................................................................................ 103
4.6.1 Importance of good earth resistance .................................................... 103
4.6.2 Three-point (Fall-of-potential) method .................................................. 104
4
Table of Contents
4.7 Transformer maintenance, repairs and testing ........................................... 109
4.7.1 Transformer 150DX3093 ...................................................................... 110
4.7.2 Preliminary tests ................................................................................... 110
4.8 Underground design for new Belle-Vue/Sottise 66kV transmission line ..... 115
4.9 Additional Design ........................................................................................ 120
4.9.1 Type of bonding for the UG cable ......................................................... 120
4.9.2 Sag calculation to determine clearance for Metro Express project at St
Louis power station ....................................................................................... 123
CHAPTER 5: ANALYTICAL TOOLS .................................................................... 131
5.1 Introduction ................................................................................................. 132
5.2 Measuring and Testing Instrument ............................................................. 132
5.3 Software Application ................................................................................... 133
CHAPTER 6: CONCLUSION ............................................................................... 134
CHAPTER 7: SUMMARY OF STATEMENT OF COMPETENCIES .................... 136
APPENDIX A ....................................................................................................... 143
APPENDIX B ....................................................................................................... 147
REFERENCES .................................................................................................... 149
ANNEX 1: TRAINING RECORD BOOK ............................................................... 151
ANNEX 2 ............................................................................................................. 152
5
List of Figures
LIST OF FIGURES
Figure 1. 1: Percentage time utilisation .................................................................. 15
Figure 2. 1: Engineering (District) Section ............................................................. 20
Figure 2. 2: The General Planning Section ............................................................ 21
Figure 2. 3: The T&P Section ................................................................................. 22
Figure 2. 4: The System Control Section ............................................................... 23
Figure 2. 5: The C&M Section ................................................................................ 25
Figure 2. 6: The P&C Section ................................................................................ 26
Figure 2. 7: The CMG Section ............................................................................... 27
Figure 3. 1: Generation, Transmission and Distribution process ........................... 30
Figure 3. 2: Typical MV overhead network ............................................................. 33
Figure 3. 3: Underground cable structure .............................................................. 38
Figure 3. 4: The ring main unit .............................................................................. 39
Figure 3. 5: Sag calculation when supports are at equal level ............................... 46
Figure 3. 6: Sag calculation when supports are at unequal levels ......................... 47
Figure 3. 7: Steps involved in 66kV overhead line project ..................................... 50
Figure 3. 8: Gantt Chart for implementation of 66kV overhead line ....................... 51
Figure 3. 9: Different layers of 630mm2 XLPE UG cable ....................................... 52
Figure 3. 10: The Daily Load Curve ....................................................................... 57
Figure 3. 11: The distribution transformer .............................................................. 63
Figure 3. 12: Oil test ............................................................................................... 66
Figure 3. 13: Layout of 66/22kV substation ............................................................ 68
Figure 3. 14: Line diagram of incoming bay ........................................................... 70
Figure 3. 15: Electrical setup of G10 generating unit ............................................. 71
Figure 3. 16: Four stroke operating cycle ............................................................... 72
Figure 3. 17: The excitation system ....................................................................... 73
Figure 3. 18: The digital 723 plus Woodward governor .......................................... 75
Figure 3. 19: The AVR ........................................................................................... 76
Figure 3. 20: Operating function of AVR ................................................................ 76
Figure 3. 21: The differential operational amplifier ................................................. 77
Figure 4. 1: Wind loading due to conductor only .................................................... 83
Figure 4. 2: Wind loading on pole alone................................................................. 85
Figure 4. 3: Bi-metallic Al/Cu lug ............................................................................ 88
6
List of Figures
Figure 4. 4: Proposed design to supply 41 housing units ....................................... 94
Figure 4. 5: LV distribution of 100kVA transformer ................................................ 95
Figure 4. 6: Single line diagram of LV distribution for distributor A (Phase R only) 95
Figure 4. 7: Current in different sections of distributor A (Phase R only) ............... 97
Figure 4. 8: Load test results................................................................................ 100
Figure 4. 9: Fall of potential method ..................................................................... 104
Figure 4. 10: Test set up for earth resistance measurement ................................ 105
Figure 4. 11: Graph of earth resistance versus percentage distance of D ........... 106
Figure 4. 12: Graph of earth resistance versus depth of rod ................................ 107
Figure 4. 13: Graph of % reduction in earth resistance v/s Number of rods ......... 109
Figure 4. 14: Dismantling and repairing of distribution transformer ...................... 111
Figure 4. 15: Testing of oil sample ....................................................................... 113
Figure 4. 16: Trench design along Terra Sugar Estate ........................................ 117
Figure 4. 17: Trench design across road ............................................................. 118
Figure 4. 18: Follow up works for Belle Vue/Sottise project ................................. 119
Figure 4. 19: Clearance for Metro Express project............................................... 123
Figure 4. 20: Survey results ................................................................................. 124
Figure 4. 21: Sag calculation ............................................................................... 125
Figure 4. 22: Work implementation on site ........................................................... 130
7
List of Tables
LIST OF TABLES
Table 1. 1: Training Schedule at the CEB .............................................................. 14
Table 1. 2: Time utilisation in each section ............................................................ 15
Table 2. 1:Plant capacity and generated voltage of CEB generating power plants 28
Table 3. 1: Overhead line clearances with respect to structures ............................ 37
Table 3. 2: 22kV Underground cable rating ........................................................... 38
Table 3. 3: Low voltage underground cable rating ................................................. 38
Table 3. 4: Safe working clearance ........................................................................ 41
Table 3. 5: Type of Towers .................................................................................... 43
Table 3. 6: Vertical clearance with respect to ground ............................................ 44
Table 3. 7: Load shedding program ....................................................................... 59
Table 3. 8: Tap changer voltage ............................................................................ 64
Table 4. 1: Calculated wind load on pole ............................................................... 87
Table 4. 2: Compliance with conditions of purchase .............................................. 89
Table 4. 3: Compliance with technical requirement................................................ 90
Table 4. 4: Summary of evaluation report .............................................................. 91
Table 4. 5: Total current on each poles of distributor A (Phase R only) ................. 95
Table 4. 6: Far end voltages on distributors A and B ............................................. 99
Table 4. 7: Phase and line voltages at far end ..................................................... 101
Table 4. 8: Earth resistance test results ............................................................... 106
Table 4. 9: Insulation resistance test before repair .............................................. 111
Table 4. 10: TTR test after repair ......................................................................... 112
Table 4. 11: Oil test results .................................................................................. 113
Table 4. 12: Voltage test result ............................................................................ 114
Table 4. 13: Load test results ............................................................................... 114
Table A 1: Factor S2 for class C (Overhead line) ................................................. 144
Table A 2: Force coefficient Cf for conductors ..................................................... 144
Table A 3: Force Coefficient on reinforced concrete pole .................................... 145
Table A 4: Factor S2 for class B (pole h<50m) ..................................................... 146
8
Acknowledgement
ACKNOWLEDGEMENT
My training at the Central Electricity Board (CEB) has been the most enriching
experience in my life. However, this would not have been possible without the help
and advice of a number of people to whom I readily express my heart-felt thanks
and gratitude.
I am very grateful for the assistance and constant supports of all my supervising
engineers.
I thank the technical officers and technicians for their willingness to share their
experience and practical knowledge with me throughout my pre-registration
training.
My heartfelt gratitude goes to the Ministry of Labour, Industrial Relations,
Employment and Training, which gave me the opportunity to undergo my training
at the CEB.
I also wish to thank my parents who have always supported me throughout my
studies and during these two years of traineeship.
Special thanks go to Mr I. Lachmansing, Mr Ismael Essackjee and Mr Dikshin
Sukhoo for their guidance and unconditional support, without which this report
writing would have been a little bit more challenging.
9
Applicant's Declaration
APPLICANT'S DECLARATION
10
Supervisor's Declaration
SUPERVISOR'S DECLARATION
11
List of Abbreviations
LIST OF ABBREVIATIONS
AAAC
All Aluminium Alloy Conductor
ABIS
Air Break Isolator Switch
AC
Alternating Current
BS
British Standard
CEB
Central Electricity Board
CT
Current Transformer
HT
High Tension
IEC
International Electrotechnical Commission
IPP
Independent Power Producer
LV
Low Voltage
MUR
Mauritian Rupees
MV
Medium Voltage
PPE
Personal Protective Equipment
PT
Potential Transformer
RMU
Ring Main Unit
SCADA
Supervisory Control and Data Acquisition
SF6
Sulphur Hexafluoride
T&D
Transmission and Distribution
12
CHAPTER 1: BACKGROUND
13
Chapter 1: Background
1.1 Introduction
I graduated from the University of Mauritius on 20th October 2015 in the field of
Electrical and Electronic Engineering. Then I joined the Central Electricity Board
(CEB) on 30th January 2017 as Trainee Electrical Engineer. During my traineeship
at the CEB, I was posted at different departments and sections under the direct
responsibility and supervision of a registered professional engineer as per Table
1.1
Table 1. 1: Training Schedule at the CEB
Section
Training Period
Supervisor
Post Held
Engineering
Section
(District Mahebourg)
Feb 2017 to Apr
Mr S.Payen
2017
RPEM: 870
Construction and
Maintenance Gang
(Production)
General planning
Mr J. Kritsnasawmy
May 2017 to Aug
2017
Mr N.Pooleecootee
2017
RPEM: 674
Nov 2017 to Dec
Mr D.Doseeah
2017
RPEM: 1127
Jan 2018 to Jul
Mr I.Essackjee
2018
RPEM: 1118
Technology &
Aug 2018 to Sep
Mr D.Seewoosunkur
Procurement
2018
RPEM: 727
Project & Construction
Construction &
Mr S.Khodabocus
Maintenance
Oct 2018 to Nov
(Workshop)
2018
(District Curepipe)
Senior Engineer
Senior Engineer
Senior Engineer
Senior Engineer
Senior Engineer
RPEM: 800
Engineering
Section
Senior Engineer
RPEM: 1136
Sep 2017 to Oct
System Control
Senior Engineer
Dec 2018 to Jan
2019
14
Mr V.Aodhora
Ag Senior
RPEM: 1266
Engineer
Chapter 1: Background
1.2 Time Utilisation
The time utilisation, as shown in Table 1.2, is based on the different tasks
performed in each section.
Table 1. 2: Time utilisation in each section
Section
Engineering
Design (%)
Engineering
Functions(%)
Allied
Engineering
(%)
Administrative
& Others(%)
55
25
10
10
30
35
30
5
65
20
5
10
System Control
40
35
20
5
Project &
Construction
Technology &
Procurement
Construction &
Maintenance
(Workshop)
65
20
10
5
5
45
30
20
30
40
20
10
Engineering
Section
(District)
Construction
and
Maintenance
Gang
(Production)
General
planning
The figure 1.1 below illustrates the time utilisation as a percentage of total time
spent on Engineering Design, Engineering functions, Applied engineering and
Administrative works.
Figure 1. 1: Percentage time utilisation
15
CHAPTER 2: TRAINING
ENVIRONMENT
16
Chapter 2: Training Environment
2.1 Introduction
This chapter describes the organisational structure of the Central Electricity Board
and gives an overview of the different sections and departments associated to the
generation, transmission and distribution of electric power in Mauritius.
2.2 Overview of the Central Electricity Board
The Central Electricity Board (CEB) is a parastatal body wholly owned by the
Government of Mauritius and reporting to the Ministry of Energy and Public
Utilities. It was established on 8th December 1952 and empowered by the Central
Electricity Board Act of 25th January 1964. The main objective of the CEB is the
sale of electricity to Mauritius and Rodrigues population through the generation,
transmission and distribution process. The Board is subdivided into the following
sections:

Production Department

Transmission and Distribution Department

Human Resource Department

Information Technology

Internal Audit Department

Corporate Planning and Research Department

Finance Department

Corporate Administration Department

Non Utility Generation Department

Customer Service Department

Supply Chain Department
The vision of the CEB is to become a world class, commercial electricity utility
enabling social and economic development of the region.
Its mission is to meet the expectations of their customers and stakeholders by:

Delivering prompt and efficient customers services.

Developing their employees and providing them with incentives.
17
Chapter 2: Training Environment

Providing an affordable, safe and reliable electricity supply.

Being the preferred employer in the region.
The CEB normally consists of three main departments:

The Production department which is involved in the generation of electric
power at thermal power stations and hydro-power plants. In Mauritius there
are 4 thermal power stations and 10 hydro power stations at Strategic
places around the island.

The Transmission and Distribution department which is responsible for
transmitting electric power from power stations to main substations and
distribute the power to consumers.

The customer service department whose goal is to meet the customers'
expectations.
2.3 The Transmission and Distribution (T&D) department
The role and responsibility of the Transmission and Distribution Department is to
transmit electric power generated from generating power plants to various
substations and distribute the power to different load centres throughout the island.
Its objective is to provide safe and continuous supply of power to consumers by
minimizing outages and operating within the statutory limit of 230V ± 6%.
The T&D Department is subdivided into different sections:

Engineering (District) Section

General Planning

Technology and Procurement

System Control

Construction and Maintenance

Meter Laboratory

Project and Construction
18
Chapter 2: Training Environment
2.3.1 Engineering (District) Section
The District Section is mainly associated to the distribution network. It helps to
improve reliability of supply by performing proper maintenance of the distribution
network from substations to low voltage (secondary) distribution level.
The distribution network can be classified as primary distribution and secondary
distribution. The primary distribution or high voltage distribution operates at 22kV
and 6.6kV, whilst the secondary distribution is the voltage supplied to consumers.
Electric power is distributed from 22kV substations to our distribution transformers
through feeders in order to supply different categories of consumers (residential,
commercial and industrial). Hence, for managing the distribution network of
Mauritius, the island is divided into three areas:

Area South which consists of Districts Mahebourg, Curepipe, Vacoas and
Souillac.

Area Centre which consists of Districts Rose-Hill, La Mivoie and Bramsthan.

Area North which consists of Districts Plaine-Lauzun, Goodlands and
Pamplemousses.
Each district is clearly defined geographically and has electrical boundaries and is
under the direct supervision of a Senior Engineer who is responsible for the
administration and control of the labour force and the works being performed within
his area. The organisational structure of a typical district section is given in figure
2.1 below.
19
Chapter 2: Training Environment
Area Manager
Senior Engineer
Administrative
Assistant
Engineer
Trainee Engineer
Principal Technical Officer
Senior Technical Officer
Technical Officer
Manual Workers
Figure 2. 1: Engineering (District) Section
The main tasks of the District Section are:

Preparing and implementing construction files.

Maintenance work on medium voltage (22kV) and low voltage (415V line
voltage); overhead and underground works.

Performing load test on existing transformers and take appropriate
measures.

Switching Operations on the Network.

Locating and repairs of network faults.
2.3.2 General Planning Section
The planning section normally deals with short-term projects initiated in response
to the application of a customer from the district concerned. The section is headed
by a Senior Engineer and is surrounded by a team consisting of planning
engineers, land surveyors, way-leave officers and draughtsman. The figure 2.2
illustrates the organisational structure of the General Planning Section.
20
Chapter 2: Training Environment
Senior Planning Engineer
Administrative
Assisstant
Wayleave Officers
Planning Engineers
Land Surveyors
Chief Draughtman
Trainee Engineer
Handymen/
Drivers
Draughtmen
Figure 2. 2: The General Planning Section
Construction files dealing with simple low voltage (LV) extension to supply a
consumer or other minor works are usually dealt within the Engineering Section.
However, for more complex projects, be it overhead or underground, where there
is a need for more complex design to extend the medium voltage (MV) network,
install new transformers and distributing low voltage to supply consumers, the
planning section caters for those.
In dealing with the projects, the planning process constitutes fulfilling the following
requirements:

Optimising the reliability of supply.

Satisfactory voltage drop (i.e. within the statutory limit of 230 V ± 6%).
A shortlist of the various types of projects dealt by the General Planning Section is:

Expansion of HT network to supply a parcelling of land.

Undergrounding overhead HT/LV network close to building.

Deviation of overhead network because of new construction.

Undergrounding of overhead network for aesthetic reasons upon request.

Supply to governmental institution and parastatal organisation.
21
Chapter 2: Training Environment
2.3.3 Technology and Procurement (T&P) Section
The quality and availability of materials used on the CEB network has a direct
impact on the reliability of supply. Therefore, it is essential to keep the stock level
of materials within a reasonable level.
The T&P Section is responsible for the procurement of materials in the T&D
department and to monitor stock level of materials through the Store Ordering
Committee held at the end of each month. The T&P section is under the
supervision of a Senior Engineer who is assisted by Engineers.
Senior Engineer
Engineers
Administrative
Assisstant
Trainee Engineers
Figure 2. 3: The T&P Section
Some of the responsibilities of the T&P are:

Monitor the stock level of materials through the Store Ordering Committee
and take necessary actions based on the availability of materials.

Preparing of technical specifications of materials for quotations and tenders.

Performing technical and financial evaluation of quotations and tenders.

Verify quality of materials delivered at Main Store from suppliers if they
comply to CEB requirements.

Manage strategic stock for cyclonic weather condition.
22
Chapter 2: Training Environment
2.3.4 System Control Section
The System Control Section is one of the most important section in the CEB
organization. It helps to control and monitor the generation, transmission and
distribution of electric power throughout the island. The System Control is headed
by a Principal Engineer and is subdivided into four sub-sections:

Operations

Supervisory Control And Data Acquisition system (SCADA) and Equipment

Radio and Communication

Protection
The section structure is as presented below in figure 2.4:
Principal Engineer
Senior Engineer
Operations
Administrative
Assistant
Cadet Engineer
Load Dispatchers
Trainee Engineer
Assistant Load
Dispatchers
Senior Engineer
SCADA & Equipment
Senior Engineer
Radio & Communication
Senior Engineer
Protection
Engineer
SCADA & Equipment
Engineer
Radio & Communication
Engineer
Protection
Senior Technical Officers
Senior Technical Officers
Senior Technical Officers
Technicians
Technical Officers
Technicians
Technicians
Figure 2. 4: The System Control Section
During my traineeship I got the opportunity to work within the Operation subsection only. Some of the roles and responsibilities of the Operation sub-section
are:

Record power generated by each units running in power stations on an
hourly basis in order to generate the daily load curve.
23
Chapter 2: Training Environment

To monitor the overall generation, transmission and distribution networks in
order to maintain the balance between supply and demand.

Maintain the frequency of the network within the required limit of 50 ± 0.2
Hz.

Carry out load shedding program in case there is an imbalance between
supply and demand.

Monitor and carry out switching operations in consultation with the district
concerned.
2.3.5 Construction & Maintenance (C&M) Section
The C&M section is divided into four subsections namely Construction,
Maintenance, Transformer Workshop and Cable. The section is headed by the
Senior Construction and Maintenance Engineer who is assisted by two Engineers
as shown in figure 2.5.
2.3.5.1 Construction sub-section:
The responsibilities of the construction sub-section are:

Construction of new substations.

Installing, testing and commissioning of power transformers and 66/22kV
switchgears.

Replacement of old and faulty equipment.
2.3.5.2 Maintenance sub-section:

Repairs and maintenance of equipment of all substations.
2.3.5.3 Transformer Workshop:

Faulty distribution transformers from different district sections are brought
for repairs and testing.
24
Chapter 2: Training Environment

The transformer workshop is also responsible for testing new transformers
before commissioning.
2.3.5.4 Cable sub-section:

This subsection is specialised in cable works consisting of cable jointing and
terminations and fault finding and repairs.
Senior Construction &
Maintenance Engineer
Engineer (Construction & Cable
sub section)
Engineer (Maintenance &
Transformer workshop)
Principal Technical Officer
Senior Technical Officer
Senior Technical Officer
(Construction)
(Maintenance)
Technical Officer
Technical Officer
Technicians
Technicians
Figure 2. 5: The C&M Section
25
Chapter 2: Training Environment
2.3.6 Project and Construction (P&C) Section
The P&C section is responsible for the transmission of electric power from
generating stations to 66/22 kV substations. Electric power transmission is done by
overhead or underground network. The supporting structures used are towers or
reinforced concrete poles.
The P&C section is subdivided into 3 sub-sections namely the substation design,
transmission line design and implementation and maintenance tower. Each
subsection is under the direct supervision of a Senior Engineer as illustrated in the
figure 2.6 below.
Principal Engineer
Senior Engineer
Substation
Senior Engineer
Transmission Line
Senior Engineer
Maintenance tower
Engineer
Engineer
Principal Technical
Officer
Senior Technical
Officer
Trainee Engineer
Technical Officer
Technicians
Figure 2. 6: The P&C Section
Some of the roles and responsibilities of the P&C section are:

Erection of new 66kV transmission line.

Construction of new substation.

Procurement of materials for the transmission network.

Maintenance of network and their equipment.
26
Chapter 2: Training Environment
2.4 The Production department (CMG)
The production department is involved in the generation of electric power by
thermal power stations and hydro power plants. The Construction and
Maintenance Gang (CMG) falling under the Production Department is responsible
for commissioning, maintaining and repairing of mechanical and electrical systems
in all CEB power plants in Mauritius.
The section is under the direct supervision of a Principal Engineer as illustrated in
figure 2.7
Principal Engineer
Senior Engineer
(CMG)
Senior Engineer
(C&I)
Engineer
Engineer
Cadet Engineer
Cadet Engineer
Trainee Engineer
Senior Technical Officer
Senior Technical Officer
Technical Officer
Technical Officer
Technicians
Technicians
Figure 2. 7: The CMG Section
27
Chapter 2: Training Environment
The CEB produce only 45% of the total generated power in Mauritius while the rest
(55%) is produced by Independent Power Producers (IPPs). Table 2.1 shows the
plant capacity and the generated voltage of CEB generating power plants.
Table 2. 1:Plant capacity and generated voltage of CEB generating power plants
Power Stations
Plant Type
Plant Capacity
/MW
Generated
Voltage
/kV
Fort George
Fort Victoria
St-Louis
Nicolay
Champagne
Ferney
Le Val
Tamarind Falls
Magenta
Reduit
Cascade Cecile
La ferme
La Nicoliere
Midlands
Thermal
Thermal
Thermal
Thermal
Hydro
Hydro
Hydro
Hydro
Hydro
Hydro
Hydro
Hydro
Hydro
Hydro
138
109.6
108
78.4
30
10
4
11.7
0.94
1.2
1
1.2
0.35
0.35
11
11
11
11
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
0.415
0.415
28
CHAPTER 3: NATURE OF
TRAINING
29
Chapter 3: Nature of Training
3.1 The Engineering (District) Section
3.1.1 Introduction: The Distribution Process
Power
Stations
Step Up
Transformer
Step Down
Transformer
22kV
66kV
Transmission over long
distances
Fuel Oil
Coal
Bagasse
Hydro
Voltage Level
increases for
transmission
Voltage Level
decreases for
distribution
(substation
66>22kV)
Distribution
Transformer
22kV>400/230 V
3-phase, 4-wire
400V
230V
Phase R
Phase Y
Phase B
Neutral
400V
400V
230V
230V
3-phase, 3-wire
Primary Distribution
Secondary Distribution
Industry, 3-phase load
House 1
House 3
House 2
Figure 3. 1: Generation, Transmission and Distribution process
The Electric power system is made up of 3 major stages:

The Generation Process

The Transmission System

The Distribution System
30
Chapter 3: Nature of Training
The District Section is mainly concerned with the distribution system. Electric
power in Mauritius is normally generated at 11 kV or 6.6 kV, transmitted at 66kV
and is stepped down to 22kV by power transformers at our main substations.
Different feeders carry the power to different distribution transformers in order to
supply customers. Hence, the 22kV voltage is further stepped down to 400V line
voltage (voltage between 2 phases) or 230V phase voltage (voltage between
phase and neutral). The Distribution system in Mauritius is a ring based system
where the feeders form a closed loop and distribution of power is done through a 3
phase, 4-wire system as shown in figure 3.1.
3.1.2 The Distribution System
The distribution system may be classified according to:

Type of construction
According to type of construction, the distribution system may be classified
as:
(a) Overhead System
(b) Underground System

Scheme of Connection
According to scheme of connection, the distribution system may be
classified as:
(a) Radial System
(b) Ring main System
3.1.3 Primary and Secondary Distribution
The distribution system may be divided into:
a) Primary Distribution
The primary distribution operates at voltages of 22 kV and 6.6 kV in
Mauritius. It is that part of the network that runs from the 66/22 kV
31
Chapter 3: Nature of Training
substations to the distribution transformers and is done through 3 phase 3wire system.
b) Secondary Distribution
It is that part which includes the range of voltages at which the ultimate
consumer utilises the electrical energy delivered to him. The secondary
distribution employs 400/230V, 3 phase 4-wire system.
3.1.4 The Overhead System
The 22 kV medium voltage (MV) overhead network in Mauritius consists of:
1) The Main Line/Feeder
The main line connects the substation to the area where power is to be
distributed. It comprises of that part of the network that links two switching
stations or originates from a switching stations. It is generally controlled at
one end or both ends by means of circuit breakers.
2) Sub Main Line
A sub-main line or main spur is comprised of the network that branches off a
main-line, having a total connected transformer capacity of 1000kVA or
more or having more than five distribution transformers connected on that
line. At the point of tap off, the sub main is controlled by an ABIS and each
distribution transformer is controlled by a set of fuses.
3) Spur
A spur is comprised of the network that branches off a main line or a submain and onto which not more than five distribution transformers with a total
connected transformer capacity of less than 1000kVA are connected. The
transformers are protected individually by a corresponding set of fuses.
The figure below illustrates a single line diagram representation of the overhead
line network:
32
Chapter 3: Nature of Training
Substation
Substation A
A
Substation B
Main line
Sub Main
Transformer
Spur
Figure 3. 2: Typical MV overhead network
3.1.5 Main components of overhead lines
Overhead lines may be used to distribute electric power. The successful operation
of an overhead line depends to a great extent upon the mechanical design of the
line. While constructing an overhead line, it should be ensured that mechanical
strength of the line is such so as to provide against the most probable weather
conditions. In general, the main components of an overhead line are:
1. Line Supports
The line supports are simply wooden or reinforced concrete poles. The choice of
supports depends mainly on whether high or low voltages are to be distributed, the
line spans and also on local conditions. For the implementations of low voltage
networks, poles of the height of 9m and 10m are normally used, while for medium
voltage networks, 11m to 15m poles are used. Also, a pole is said to be of
composite type, when used to support both medium and low voltage
simultaneously.
33
Chapter 3: Nature of Training
2. Cross-arms
Cross arms act as holders that support the conductors on insulators attached to
poles. They are fixed at a certain height so as to keep the conductors at suitable
level above ground and to provide reasonable clearance between the conductors.
Cross-arms can be either wooden or metallic.
Bare conductors are normally supported on poles using wooden cross-arms. The
standard dimensions of wooden cross-arms are: 1800mm (6ft)- 2400mm (8ft)3000mm (10ft).
Metallic cross-arms are now being employed since they offer better resistance to
the forces transmitted to poles by the conductors and do not rot easily.
3. Fittings
During implementation of LV extension or fault repair, several types of materials
are used. Fittings are used to support cables and exist as suspension type, single
anchor clamp, double anchor clamp and LV connector for service line.
4. Insulators
Insulators on overhead line conductors prevent currents from conductors to flow to
earth through line supports; i.e. they insulate line conductors from support.
Insulators are made of high resistance insulation material and have good
mechanical strength to withstand the conductors load and wind load. The different
types of insulators used on the network are the pin type, suspension type and
strain type.

Pin type insulator:
The pin-type insulator is made of porcelain and is normally installed on the
cross arm. The insulator is screwed on a spindle which is mounted on the
cross arm and the conductor is tightened at the top on the insulator groove.
34
Chapter 3: Nature of Training

Suspension type Insulators:
They consist of a number of porcelain discs connected in series by metal
links in the form of a string. One end is fixed on the cross-arm and the line
conductor is attached to its lower end.

Strain insulator:
The strain insulator is a similar to the suspension insulator except that it is
used to sustain greater pulls. Sometimes a line must withstand great strain,
for instance at a corner, at a sharp curve, or at a dead-end. In such a
circumstance the pull is sustained and insulation is provided by a strain
insulator.
5. Lightning arresters
The purpose of lightning arresters on the network is used for protection against
voltage surges due to lightning and switching operation. These over-voltages can
cause breakdown of the various equipment on the power system.
6. Conductors
For the distribution of electric power, insulated twisted cables (torsadé cables) and
bare conductors are normally used.

Bare Conductors
The overhead bare conductors used on the CEB network are made up of All
Aluminium Alloy (AAAC) or SILMALEC (Alloy of silicon, magnesium and
aluminium).
Bare conductors are more commonly employed for primary distribution. The
sizes of overhead bare conductors that are more often used for MV network
are 25mm2, 50mm2, 100mm2 and 150mm2 and their current carrying
capacity are 190A, 295A, 450A and 585A respectively.
35
Chapter 3: Nature of Training

Insulated twisted cable (Torsadé cables)
The torsadé cable consists of multiple conductors of aluminium each
individually insulated with XLPE (cross linked polyethylene) coating and are
twisted together with a messenger in order to improve their capability to
withstand mechanical stress.
The LV torsade cable consists of 3 phase, a neutral and a conductor for
street lighting. The MV torsade cable consists of 3 phases and a messenger
to hold the three phases in a more compact way and be able to withstand
mechanical stress.
The torsade cables used for HT primary distribution are:
-
3 x 35 + 50 mm2
-
3 x 95 + 50 mm2
-
3 x 150 + 50 mm2
The torsade cables used for LV distribution network and service lines are:

Torsade for LV distribution network:
-
3 x 70 + 54.6 + 16 mm2
-
3 x 35 + 54.6 + 16 mm2

Torsade for service lines:
-
2 x 25 mm2
-
2 x 16 mm2
7. ABIS- Air Break Isolated Switch
ABIS commonly used on the distribution network act as a mechanical operated
switch. It is installed at strategic locations to enable the technical personnel to
effect isolation of part of the network for maintenance. It provides visible isolation of
part of the line that has been switched off. ABIS are also used to ring two feeders,
at boundary locations or at regular intervals along a main line.
36
Chapter 3: Nature of Training
3.1.6 Overhead line clearances with respect to structures
When implementing overhead network, the following clearances need to be
respected relative to any building.
Table 3. 1: Overhead line clearances with respect to structures
Voltage /V
400/230 V
6600 V
22000 V
Type of
Conductor
Horizontal
Clearances (m)
Vertical clearances
(m)
Bare
3.0
3.0
Insulated
0.5
2.0
Bare
3.8
3.2
Insulated
0.5
2.0
Bare
Insulted
3.8
0.5
3.2
2.0
3.1.7 Underground Network
3.1.7.1 Introduction
Electric power may be distributed by overhead system or underground cables. The
underground system has several advantages, some of which are:

Less liable to damage by cyclones or trees or accidents.

Less chances of faults.

More aesthetic
However, although the cost of installation is high, the CEB is trying to underground
most of the overhead network as it involves less maintenance cost and it increases
the reliability of supply as there is less chance of fault occurring.
3.1.7.2 Underground Cables
Underground cables essentially consist of one or more conductors covered with
suitable insulation and surrounded by a protecting cover. Although several types of
cables are available, the type of cable to be used will depend upon the working
voltage.
37
Chapter 3: Nature of Training
The underground cables used for primary and secondary distribution are as per
tables 3.2 and 3.3 below.
(i) For primary distribution i.e. 22kV
Table 3. 2: 22kV Underground cable rating
UG Cables- 22kV
Current Rating
3 × 35 mm2 AL (XLPE)
155
3 × 95 mm2 AL (XLPE)
270
2
3 × 240 mm AL (XLPE)
345
2
3 × 300mm Cu (XLPE)
594
(ii) For secondary distribution i.e. 415 V
Table 3. 3: Low voltage underground cable rating
UG Cables- 22kV
Current Rating
4 × 25 mm2 AL (XLPE)
110
2
4 × 95 mm AL (XLPE)
236
2
4 × 240 mm AL (XLPE)
354
2
1 × 240mm AL (XLPE)
424
1 × 500mm2 Cu (XLPE)
765
2
The 3 × 95 mm AL (XLPE) high voltage distribution cable is as shown in figure
3.3. It consists of three cores (conductor) used for three phase service. Each core
or conductor is provided with a suitable thickness of insulation, the thickness of
layer depending upon the voltage to be withstood by the cable. The armouring is
made of galvanized steel wire.
Figure 3. 3: Underground cable structure
38
Chapter 3: Nature of Training
3.1.7.3 Ring Main Units (RMU)
The SF6 insulated ring main unit is a compact switchgear for application in
underground medium voltage distribution networks. There are different types of
RMUs depending on incoming and outgoing feeders and outgoing transformers.
The most common RMUs used on the network are:

2 +2 where there are ‘2’ feeders and ‘2’ outgoing transformers

3+1 where there are ‘3’ feeders and ‘1’ outgoing transformer
22kV Busbar
Earth
Fuse
Fuse
TX 1
Incoming Feeder
Outgoing Feeder
TX 2
Figure 3. 4: The ring main unit
RMUs enable:

Two or more feeders to be interconnected to improve reliability of supply in
an area by setting up a ring circuit.

One or more transformers to be connected to the distribution network

Maintenance of network to be carried out with minimum outages.
39
Chapter 3: Nature of Training
3.1.8 Health and Safety
3.1.8.1 Safety Measures at work
At the CEB, safety at work is a measure that is very essential and every worker or
employee has to strictly abide to it. Employees have to carry out risk assessments
prior to any task on network to avoid electric shock or electrocution. Therefore,
before performing any operation on the CEB electrical network, the following
procedures are mandatory.
1. Switch off the system by opening circuit breakers or make it dead.
2. Isolate the system from all possible sources of supply by opening ABIS.
3. Lock in open position circuit breakers, switches etc.
When an authorised person is to proceed to an isolation, he shall install
personal padlocks wherever applicable and affix safety labels to avoid the
system being re-energized.
In exceptional cases where padlocking arrangements cannot be effected,
the authorised person shall station a person near the point of isolation. This
person will ensure that the switch position is not altered while work is in
progress.
4. Test- The authorised person shall test on site, by means of voltage detector,
the circuit and ascertain that the system on which work is to be carried out is
not live
5. Earthed- After the system has been made dead and isolated from all
possible sources of supply, earthing equipment must be used to connect it
to ground.
6. Issue permit-to-work certificate to proceed with work.
3.1.8.2 Safe working clearances
When carrying out work in the vicinity of live conductors, no workman shall enter
beyond a position in which it would be possible for him to bring any part of his body
or any working tool or material within the distances of any exposed live conductor,
as listed in Table 3.4 below.
40
Chapter 3: Nature of Training
Table 3. 4: Safe working clearance
Rated Voltage
Minimum Clearances
Not exceeding 1000 V
1m
Exceeding 1000 V but not exceeding 33 kV
1.2 m
Exceeding 33 kV but not exceeding 66 kV
1.8 m
Exceeding 66 kV but not exceeding 145 kV
2.2 m
3.1.8.3 Personal Protective Equipment (PPE)
The provision and use of personal protective equipment is regarded as a means of
avoiding or minimizing injury and the use of such equipment is mandatory at all
times when there is a risk of bodily injury against which the equipment affords
protection.
1. Safety Helmets
Safety helmets shall be used in situations where there exist the risks of objects
falling in the head, the danger of being struck by swinging loads or the hazard of
striking the head against stationary objects. Only helmets of non conductive type
shall be used.
2. Safety Gloves
Safety gloves shall be worn to provide protection to the hand against cut, abrasion,
heat burns when performing work such as pole climbing, tree lopping, handling of
sharp or rough materials and so on.
3. Safety Belt
The use of safety belts when working on poles or high structures are compulsory.
4. Safety Shoes/Boots
They provide protection to the feet against falling objects, when striking against
objects or when stepping on sharp protrusions.
41
Chapter 3: Nature of Training
3.2 The Project and Construction (P&C) Section
3.2.1 Introduction
The electric supply system in Mauritius is made up of the generation process,
transmission system and the distribution system. The Project and Construction
department deals with the transmission part of carrying electric power from our
generating stations to our major substations throughout the whole island.
3.2.2 The Transmission Network
Electric power is generated at 11kV and 6.6kV by thermal stations and
hydroelectric power plants respectively. This voltage is then stepped up by power
transformers and is transmitted at 66kV for economic purposes.
The 66kV transmission network in Mauritius is a ring based system in order to
improve reliability of supply. The electric power is transmitted by means of
underground cables and overhead lines. The total length of the transmission
network is 326 km with underground cables covering 26 km and overhead line
around 300 km.
3.2.3 Overhead line transmission
The overhead transmission line transmit bulk power over long distances. Power is
transmitted by using line supports which are towers and reinforced concrete poles.
The choice of using either depends upon the environmental conditions, span
length, number of circuits and so on.
3.2.3.1 Towers
Towers are manufactured in a number of different designs to accommodate
different:
(1) Voltage levels
(2) Span length
(3) Ground profiles and environmental conditions (River crossing)
(4) Angle of line (deviation from straight route)
(5) Number of circuits
42
Chapter 3: Nature of Training
The size of the tower is affected by the rated voltage, clearances and the
mechanical load it is required to carry.
Transmission line conductors are strung on in-line suspension towers and strain
(angle) towers. The suspension tower is typically employed along straight section
of the line route, while the strain towers are used where there is a bend in the
power-line alignment.
The strain tower is of heavier construction to compensate for the forces applied
including the conductors and wind loading while suspension towers are of lighter
construction as it supports the weight of the conductors without tension.
Depending on the angle of deviation of the transmission line, towers can be
categorised into 5 types as illustrated in table 3.5 below.
Table 3. 5: Type of Towers
Type of
Tower
A
Tower Duty
Used on straight lines up to 2° deviation
B
Small angle tower used on line deviations
from 2° to 15°
C
Medium angle tower used on line
deviation from 15° to 30°
D
Large angle tower used on line deviation
from 30° to 60°
E
Large angle tower used on line deviation
from 60° to 90° and used as line terminal
tower.
3.2.3.2 Pole Mounted Transmission Line
Insulator Type
Suspension
Strain
Strain
Strain
Strain
Another overhead method for transmitting electric power over long distances is
pole mounted transmission system. Reinforced concrete poles of 14m are normally
used. Poles configuration can be single type poles or H-poles. The selection of the
poles depends upon the span length and ground profiles of the line routing.
Furthermore, when designing a 66kV overhead pole mounted transmission
network, it is very important to have safe vertical clearance from ground. Therefore
sag calculation is very important.
43
Chapter 3: Nature of Training
3.2.3.3 Conductors
In order to increase the conducting properties of conductors, improve their
performance in corrosive environment and retain sufficient mechanical strength,
homogeneous all alloy conductors with different sizes and stranding are being
employed. The standard, most common material is aluminium-magnesium-silicon
alloy wire also referred to as All Alloy Aluminium conductor (AAAC).
For CEB overhead transmission network, ASTER 366 and ASTER 570 are used,
which are both all alloy aluminium conductors. The choice of the conductor
depends on the power that needs to be transmitted. ASTER 366 consists of 37
strands while ASTER 570 is made up of 61 strands, having maximum current
carrying capacity of 800A and 1200A respectively.
3.2.3.4 Clearances and Sag
1. Clearance
The overhead transmission line is designed with respect to the required clearances
that need to be allocated. The normal clearances for overhead 66kV lines are as
shown in the table below.
Table 3. 6: Vertical clearance with respect to ground
Clearance to ground
Vertical (m)
Across road
6.1
Along road
2. Sag
6.1
When erecting transmission line, it is important that the conductors are under safe
tension. If the conductors are too much stretched, the stress in the conductor may
cause the conductor to break due to excessive tension. Therefore, the conductor is
allowed to have a sag.
Sag is defined as the vertical distance between the point of support on the poles
and the lowest point on the line.
44
Chapter 3: Nature of Training
The sag is as a result of the tensioning of the line and must not be too low
otherwise the safety clearances may not be met.
(i) Sag calculation when supports are at equal level
The sag for a conductor between two equilevel supports is given by the formula:
Sag, S =
......................................................................................... equation:(1)
where,
L = Length of span
W= Weight per unit length of conductor
T = Tension in the conductor
In our case for sag calculation, the ASTER 570 conductor was chosen.
ASTER 570

Weight = 1574 kg/km

Tensile Strength = 185.3kN

Safety factor = 10

Span Length = 70m
45
Chapter 3: Nature of Training
Figure 3. 5: Sag calculation when supports are at equal level
The figure above illustrates the sag in ASTER 570 conductor for a span length of
70m. Therefore,
Weight of conductor/meter run, W = 1574/1000 = 1.574 kg.
Working Tension, T =
= 1888.89 kg
Sag, S =
=
= 0.51m
Therefore, vertical clearance of the lowest conductor to ground = 9.8-0.51
= 9.3 m,
which satisfy the required clearance.
46
Chapter 3: Nature of Training
(ii) Sag calculation when supports are at unequal level
In hilly areas, we generally come across conductors suspended between two poles
at unequal levels. Following our above example, figure 3.6 illustrates the ASTER
570 conductor suspended between two 14m poles which are at different ground
levels.
S2
1.8m
h
S1
9.8m
x1
x2
L
Vertical clearance of lowest conductor to
ground
θ
2.4m
a
b
p
Ground
Figure 3. 6: Sag calculation when supports are at unequal levels
Let,

L = Length Span

h = Difference in levels between the two poles

= Distance of lower pole from lowest point of conductor

= Distance of upper pole from lowest point of conductor

T =Tension in the conductor

W = Weight per unit length of conductor
Then, Sag is given by:
=
......................................................................................... equation:(2)
47
Chapter 3: Nature of Training
=
......................................................................................... equation:(3)
where,
=
and
=
By finding the values of
and
, values of
and
can be easily calculated.
Hence, following the previous example above, the vertical clearance from ground is
calculated.

Effective height of each pole from ground to point of support is 9.8m.

Assume b = 1m

Difference in levels between the two poles, h = 1m

Horizontal distance between the pole is assumed to be 70m i.e. the span
length

Therefore,

Solving for

Applying

θ=
+
= 70m
and
from above equation, we get
in equation (3),
( ⁄ )
( ⁄
= 18m and
= 52m
= 1.13m
)
°
Therefore, vertical clearance of lowest point on conductor from ground is:
(
)
(
)
( tanθ)
=(
)
(
)
=9.41m, which satisfy the required clearance.
48
Chapter 3: Nature of Training
3.2.3.5 Line Inspection
The task of maintaining and inspecting high voltage transmission line can be
difficult and dangerous, mainly for towers. This necessitates to switch off the part
of the network where inspection is required to be done. During my training I
participated in introducing the use of drone technology for line inspection. Drone
helps to improve reliability of supply and imposes less risks on CEB personnel from
any potential hazards. Accessing areas of high voltage power lines either when
conducting routine inspection or surveying damage after cyclones may be easily
carried out with the use of drones
3.2.4 Project Management in implementing 66kV overhead transmission line
Before starting any project it is important to have a good project planning in order
to have a proper understanding about the objectives and goal of the project.
Project management for transmission line installation is very important. The reason
for such importance is the level at which the resources are at stake for such
project.
Projects normally have three interrelated objectives, which are to:

Finish on time

Meet and satisfy the requirements of the project (scope)

Meet the budget
As work progress on a project, unexpected problems may usually arise that will
threaten to throw the project off schedule. Project management involves applying a
schematic approach to achieve the objectives of the project, and when the project
management is done properly, the probability of a successful outcome to the
project is increased.
During my traineeship at the P&C, I got the opportunity to follow up works at BelleVue/Sottise. In order to improve reliability of supply in this region a second 66kV
overhead transmission line was being implemented. The project was broken down
49
Chapter 3: Nature of Training
into a number of subsidiary tasks and project management tool (Gantt Chart) was
used to schedule each of these respective tasks.
The different steps involved in the project are as described in figure 3.7 below.
Implementation of
66kV Overhead
Transmission Line
Site Survey
Network Design
 Tree Lopping
 Obtain wayleave
 Peg location for poles
Cost Estimate
 Line routing
 Type of poles to be used
 Cable Sizing
 Materials
 Transportation
 Labour
Tasks






Excavation of holes
Transportation of poles
Erection of poles
Concreting of poles
Erection of stays
Stringing of conductors
Figure 3. 7: Steps involved in 66kV overhead line project
Therefore, from the diagram above it can be observed that when initiating the
project, a site visit was conducted to examine the ground profiles and
environmental conditions. The site plan was obtained to scale from the drawing
office and the line routing was proposed. The appropriate line support was chosen
and the cable was sized accordingly depending on the power that need to be
transmitted. The exact locations of each poles were pegged and necessary wayleaves were obtained. Tree lopping is applicable only when there is the need for
access creation. The cost estimate for materials, transport and labour was
prepared and finally the implementation process was supervised according to the
Gantt Chart below.
2. Gantt Chart
The Gantt Chart prepared illustrates the implementation phase of a portion of the
66kV line routing. The Gantt Chart is a useful way of showing what work is
scheduled to be done on a specific day. It also helps us view the start and end
dates of the implementation process in one simple view.
50
Chapter 3: Nature of Training
Figure 3. 8: Gantt Chart for implementation of 66kV overhead line
3.2.5 The Underground Transmission network
Overhead transmission network is more vulnerable to external causes like
cyclones, lightning etc. Therefore, the application of underground system is
becoming more frequent. However, due to their high installation cost, their use is
limited. Underground cables are directly buried in ground or laid inside pipes.
3.2.5.1 Underground cable
The underground cable used for transmission of 66kV voltage is a single core
conductor, 630 mm2 XLPE copper cable. A typical construction of the UG cable is
as shown in figure 3.9 below. The various parts are:

Conductor: Copper

Conductor Screen: Semi-conductive

Insulation: XLPE

Insulation Screen

Water blocking tape: Non conductive

Copper wire screen

Aluminium foil

Outer sheath
51
Chapter 3: Nature of Training
Figure 3. 9: Different layers of 630mm2 XLPE UG cable
3.2.5.2 Laying of underground cables
The reliability of the underground network depends to a considerate extent upon
the proper laying conditions of the cable. There are two main methods that is
employed in CEB underground transmission network of laying underground cables.
(i) Direct laying
This method of laying UG cables is simple and effective. In this method a trench is
dug to the required depth and width. It is then backfilled with a layer of rocksand
and the cables are laid. The rocksand is used as it allows pulling the UG cables
without causing any serious damage to the outer layer of the cables. Once laid, it is
covered with yet another layer of rocksand. On top, warning slabs are placed to
inform other services like CWA, Telecom etc. of the presence of CEB UG cables.
The trench is further backfilled with loose soil. Finally, warning tapes are placed
along the whole area of the trench. The warning tapes and warning slabs are
safety measures to avoid any unnecessary hazards.
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Chapter 3: Nature of Training
(ii) Laying in pipes method
In this method of laying, the cables are placed inside pipes which are laid along the
cable route. This method is normally employed on road crossing. The backfilling
process is same as the direct laying method except that concrete is used instead of
rocksand and crusher run in place of loose soil.
3.3 Technology and Procurement (T&P) Section
3.3.1 Introduction:
The electrical network (Transmission and Distribution) in Mauritius is comprised of
different types of materials and equipment. The quality and availability of materials
used affects reliability of supply. Hence, proper use of good quality materials is
recommended. The availability of these materials is crucial for the proper operation
of different sections that fall under the Transmission and Distribution department.
Therefore, the role of the Technology and Procurement section is to ensure that
availability of materials is continuous by monitoring their stock levels. Quotations or
tenders are launched whenever stock levels of materials reaches a minimum level.
During my traineeship in this section, I was involved in the technical and financial
evaluation of quotations.
3.3.2 The Store Ordering Committee
At the CEB, all the transactions performed in each and every sections are recorded
and maintained up-to-date by a computerised database (SAP Software). This helps
to have an overview of quantity of materials being utilised for each project and
enables efficient materials management. All the materials used in the CEB is
recorded in the above-mentioned database and each material has a predefined
minimum level allocated based on yearly rate of use.
The Store Ordering Committee is held at the end of each month so as to keep
track and monitor stock level of materials and thus recommendations are made, if
necessary, of whether quotations and tenders need to be launched for materials
procurement. The Store Ordering Committee normally consists of a Principal
Engineer (for Distribution), Senior Engineer and Engineer of the T&P section,
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Chapter 3: Nature of Training
District Engineer, Supply Chain Executive, Principal Store Officer and Trainee
Engineers. The Principal Engineer acts as the chairman of the committee and
takes decision of the materials to be procured and in which quantity.
3.3.3 Launching of Tenders or Quotations
Following the store ordering committee, tenders or quotations are launched by the
procurement section. Normally, quotations can be launched both for local and
overseas bidding for estimated amount not exceeding MUR 2,000,000.
However, if are to be procured locally, quotations are launched for an estimated
amount not exceeding MUR 500,000.
Otherwise, for an estimated amount exceeding MUR 2,000,000, tenders are
launched which can either be open advertised bidding or restricted bidding
exercises.
3.3.4 Steps involved in the analysis of Quotations
3.3.4.1 Quotation Procedure
Once the Store Ordering Committee has decided upon which materials and how
many need to be ordered, a purchase requisition is issued by the Principal Store
Officer. The purchase requisition is then released by the senior engineer of the
T&P section. Afterwards, the procurement section sends Request For Quotation
(RFQ by fax) to different potential bidders. After having received the requested
quotations from the bidders, opening of bids is carried out. The Procurement
section then performs a preliminary evaluation and sends the bids to the Materials
section. The Engineers at the Materials section carry out financial and technical
evaluation of the bids.
3.3.4.2 Evaluation stage of quotation
Technical evaluation of the quotation involves different details that need to be
taken into consideration as listed below:

The offer proposed by the supplier is verified if it meets the terms and
conditions (mode of payment, validity period etc) stipulated by the CEB.
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Chapter 3: Nature of Training

It is then checked if the properties of the materials comply with the
standards of IEC (International Electrotechnical Commission) or BS (British
Standards).

Suppliers test reports attached are analysed (if test comply with the required
IEC) and it is required that the manufacturer is ISO certified.

Submitted drawings of the material are verified to check whether the
material is suitable for CEB usage.

If in case some further information are required from the supplier, queries
are sent to request for clarification.

These steps are repeated for each and every bidder and the bidder which is
technically responsive is selected.
Financial evaluation is then carried out by ranking the bidders with respect to their
quoted price.
After successful evaluation of the quotation, a Purchase Authorisation Form (PAF)
is filled (by the Senior Engineer of the T&P section) and a Purchase Order (PO) is
issued by the Procurement section and sent to the successful bidder.
3.3.5 Request for inspection
After choosing a bidder, it is sometimes required to have an inspection of the
materials at the manufacturer's place. Request for inspection is launched only if
inspection is required. Sample test reports are asked to manufacturers in case
inspection is not required.
Inspection is carried out at manufacturer's premises by CEB's designated
Inspection Agent. After having selected the particular bidder, a request for
inspection of the materials is sent to the Supply Chain Executive of the CEB by the
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Chapter 3: Nature of Training
Contract Management Office.
A quotation is sought from the usual inspection
service providers.
Pre-Shipment Clearance shall be given by the chosen independent inspectors,
after approval of the tests and submission of all test reports and related
documents. An inspection note is delivered to the manufacturer for releasing the
goods for shipment if inspection is satisfactory. Otherwise, a non acceptance note
listing the deviations from specifications is given if inspection is unsatisfactory.
After shipment has been approved and materials delivered at the Main Store of the
CEB, the Engineers at the T&P have to check the materials for conformity to CEB's
specifications. An inspection of goods report is then issued so that the materials
can be recorded on the stock and payment can be done to supplier.
3.4 System Control Section
3.4.1 Introduction
The System Control Section maintains the equilibrium between power supply and
demand. It helps to control and monitor the generation, transmission and
distribution of electric power throughout the island via the SCADA (Supervisory
Control and Data Acquisition) system. During my training I got the opportunity to
work in the Operation sub-section only and it is described as follows.
3.4.2 The Daily Load Curve
The load on the network is never constant; it varies continuously. The load
variations during the whole day (i.e. 24 hours) are recorded at regular time
intervals and are plotted against time in order to generate the daily load curve.
Figure 3.10 shows a typical daily load curve. It is clear that load is varying being
maximum at 6:30 P.M. in this case. The various colours represents the different
power stations running to meet consumer demand. From midnight to 5 A.M, the
demand is low. It then rises to a relatively high value known as morning peak at
around 10.30 A.M. From 10.30 A.M to 4 P.M, load on power stations remains
almost constant. At around 6:30 P.M, curve reaches a maximum value of around
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Chapter 3: Nature of Training
380 MW, known as evening peak. This maximum value is also referred to as the
maximum demand of the day. Normally, the time at which the peaks (morning and
evening) occur varies during winter and summer. Finally, from 6:30 P.M to
midnight, load on power stations keeps on decreasing.
Figure 3. 10: The Daily Load Curve
3.4.3 Frequency Control
The system frequency is ideally 50 Hz with an allowable deviation of ±0.2 Hz and
this frequency is achieved when power generated equals demand. However, this is
not always possible because frequency will continue to fluctuate since the demand
on the system is never constant. The variation in frequency is carefully monitored
by the operators and appropriate actions are taken to maintain the frequency within
the permissible limit.
Hence, in order to maintain the system frequency within the required limit, the
following methods are normally used:
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Chapter 3: Nature of Training
Primary Frequency Control: This method is carried out at generating station. This
is achieved by making some generators on the network operate in frequency
control mode. Thus, they automatically respond to frequency changes on the
network by increasing or decreasing their rotor speed and power output as a result
of their governor action.
Secondary Frequency Control: This is achieved by adding or removing
generators on the grid as per the operators’ instructions.
3.4.4 Voltage Control
Voltage fluctuation is due to the continuous variation in load. This results in the
increased/decreased voltage available at receiving end (consumers' terminals).
This is undesirable because it may cause malfunction or damage of consumers'
appliances. Therefore, in order to keep the receiving end voltage within permissible
limit, the following methods are used:

At power stations, voltage is controlled by varying the excitation of the
alternators.

At the substations, voltage is regulated by activating the on load tap
changers of power transformers. In order to monitor the 66kV and 22kV
voltages in the substations, potential transformers are installed on both bus
bars. The turns-ratio of the power transformer is varied from the System
Control in order to regulate the distribution voltage. By changing the tap, the
voltage in the secondary circuit is varied and voltage control is obtained.

Voltage is also regulated by compensating for the reactive power in the
network through the use of capacitor banks installed at various substations.
3.4.5 Spinning Reserve
The spinning reserve is normally equivalent to at least the power production
capacity of the largest unit on the network. In Mauritius, the largest power
generation unit is at CTSAV with a capacity of 37 MW. In case of a breakdown of
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Chapter 3: Nature of Training
the unit during generation of power, the spinning reserve should be able to
compensate for this power outage and hence restore the system frequency.
Therefore, it is important to always keep a safe and sufficient spinning reserve.
Some generators are normally run below their rated capacity in case a shortfall of
power occurs and system frequency need to be restored. However, in case one or
more large generating units on the network fail and spinning reserve is not
sufficient to compensate for this power outage, an automatic process known as
automatic load shedding occurs.
3.4.6 Automatic Load Shedding
Load shedding is activated when the largest unit on the network has failed or two
or more units have failed and spinning reserve is not sufficient to restore system
frequency. The load shedding process is an automatic process of disconnecting
pre-selected feeders from the network when system frequency has dropped below
a preset value of 48.6Hz. The process normally consists of 6 levels as shown in
table 3.7.
Table 3. 7: Load shedding program
Level
Frequency/Hz
1
48.6
2
48.4
3
48.2
4
48.0
5
47.8
6
47.6
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Chapter 3: Nature of Training
The pre-selected feeders are normally those which do not supply essential
services like hospitals, clinics, water pumps, etc.
3.5 General Planning Section
3.5.1 Introduction
In this section, I got the opportunity to learn about the procedures involving the
planning and preparation of cost estimates regarding application for supplying an
NHDC plot of land. Electricity request by any client is termed as a project and is
designed in the most economical and technically reliable way.
3.5.2 The Planning Procedures
The planning section deals with short-term projects normally initiated upon the
application of a client. Upon submitting all legal documents such as site plan and
location, land deeds etc, the planning procedures starts with the preparation of a
construction file concerning the client's project.
Projects are planned so as to be:

Economical and safe to implement.

Technically reliable.

Environmental friendly.

Extendable (for future use).
The procedures below involve the planning process to implement a project.
1. Meeting with the client
Meeting with client to determine the site location and discuss about details of load
requirement. A load list is requested from client, which includes the diversity factor.
2. Site visit and survey
A preliminary field survey is carried out to evaluate the practical implication of the
project and the following information are gathered:

Type of existing network (MV, LV, Overhead, Underground).
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Chapter 3: Nature of Training

Distance of the nearest network to the proposed project.

Load being supplied to the region for ultimate decision whether the
proposed project can be supplied from existing network.

Information concerning the existing services along the proposed line routing
(e.g. CWA, sewerage, telecom) if underground required by client.

Alternative solution are also analyzed on site.
Following the survey on site, a set of drawings from the drawing office for the
existing MV and LV network in the area are requested. The existing system layout
of the region concerned is examined to determine the feasibility of the project.
3. Way-leave procedures
Way-leave officers are responsible for seeking way-leave for erection of lines,
stays, transformer etc.
4. Design of the project

Voltage drop is calculated in order to ensure that the receiving voltage at the
far end of the distributor is within the permissible limit of 230 V ± 6%.

Calculation of cable current carrying capacity to determine the size of cable.

Poles to be used and fittings.
5. Preparation of cost estimate
The preparation of the cost estimate include:

Material Cost :
Cost estimate is prepared for erection of HT network, erection of transformer
and erection of LV network.

Labour/Transport Cost:
The CEB/Contract labour and transport cost include:
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Chapter 3: Nature of Training
-
Strength of labour force and number of working hours required.
i.e. whether the work will be implemented by CEB labour or by
Contractors or both and
whether project will be implemented on
normal working hours or overtime.
-
Preparation of rates to be paid to contractors.
-
Preparation of rates for transportation of materials to and from sites.
6. File recommendation and Approval
After the cost estimate has been prepared, the file is sent to the Senior Planning
Engineer for recommendation. An official letter is sent to the client to settle
payment by the Area Manager. Once the payment is carried out by client, the
construction file is sent to the District concerned for the implementation process.
3.6 The Construction and Maintenance (C&M) Section
3.6.1 Introduction
The roles and responsibilities of the C&M section is to repair and maintain
distribution transformers, power transformers and to construct and maintain
substations and their equipment throughout the whole island. Power transformers
and distribution transformers play an important role in the transmission and
distribution system. Therefore, it is essential to carry out proper maintenance and
tests.
3.6.2 The distribution transformer
Alternating voltage can be raised or lowered as per requirement in the generation,
transmission and distribution process. This is possible by using a static device
known as a transformer. The transformer works on the principle of mutual
induction.
The distribution transformer shown in figure 3.11 is used to step down medium
distribution voltage of 22kV or 6.6kV to low voltage distribution of 400/230V. The
transformers used are of capacity 25, 50, 100, 150, 250, 500 and 1000KVA
depending upon load demand.
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Chapter 3: Nature of Training
Figure 3. 11: The distribution transformer
3.6.3 Main components of the distribution transformer
(i) The Core
The core of the transformer is divided into two parts. The vertical portion on which
the coils are wound is referred to as the limb while the top and bottom horizontal
portion is known as the yoke of the core. The core is made up of laminations.
Because of the laminated type of construction, eddy current losses get minimized.
The core provides a path for magnetic flux to link the primary and secondary
windings.
(ii) The windings
One of the two coils is connected to a source of alternating voltage. This coil in
which electrical energy is fed with the help of the source is known as the primary
winding. The other winding is connected to load. This winding is called the
secondary winding. The size of the coils depends on the amount of current that will
flow through it. In step-down transformers, the primary windings are of smaller
cross-sectional area whereas the secondary coils much larger in size.
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Chapter 3: Nature of Training
(iii) Transformer Oil
The core and windings of the transformer are immersed in oil. The oil serves for
insulation and cooling purposes. For distribution transformers mineral insulating oil
is normally used. Any impurities in the oil are removed using an oil filtration plant.
(iv) Tank
The tank contains the core and the windings and is filled with oil. It is made of
galvanized iron.
(v) Bushings
Bushing of transformers can be of porcelain type or plug-in type. They are used to
insulate the live conductors from the earthed transformer tank. The internal
windings of the transformer are connected to the external network via the
bushings.
(vi) Tap changer
The presence of a tap changer is to regulate voltage along the line. If the
secondary line voltage is observed to be falling below or going beyond tolerable
values, then the primary voltage has to be regulated. A number of tapings as
shown on table 3.8, are provided on the primary side of the transformer and thus
the voltage can be adjusted accordingly by changing the number of primary turns.
Table 3. 8: Tap changer voltage
Tap Position
Primary Voltage
/(V)
1
23100
2
22550
3
22000
4
21450
5
20900
64
Secondary Voltage
/(V)
415V
Chapter 3: Nature of Training
(vii) Fins
They are used to increase the surface area to volume ratio of the transformer,
which increases the rate of cooling.
(viii) Drain valve
The drain valve is situated at the bottom of the transformer and is used to easily
remove the oil during maintenance and repairs.
3.6.4 Power transformer
These transformers are used for stepping up or down the voltage levels for
transmission or distribution purposes. In generating stations, they step up voltage
form 11kV to 66kV for transmission purposes. In substations, they step down the
voltage from 66kV to 22kV for distribution.
3.6.5 Tests performed on distribution transformers
The transformer workshop sub-section is responsible for maintaining, repairing and
testing of all distribution transformers brought from all district sections throughout
the whole island.
After performing a visual inspection and confirming no external damage or oil
leakage was observed, the following tests are normally carried out.
1. Continuity test and Insulation test
The continuity test is carried out to verify open circuits, i.e. whether the coils of the
transformer are opened or not. Insulation resistance is measured between each
phase and the transformer frame as well as between each MV phase and LV
phase. It gives an indication of the state of the insulation between MV and LV
windings and between MV and the frame of the transformer. A transformer in good
working condition should have resistance greater than 500 MΩ.
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Chapter 3: Nature of Training
2. Transformer Turns Ratio (TTR) test
The TTR test measures the ratio of the number of turns of the MV and LV
windings. The test is repeated for each tap position in the transformer. The aim of
the test is to determine that the tap changer has been correctly connected and
operating properly.
3. Dielectric test of oil

One terminal of the test jar is connected to a source of supply. The other
terminal is earthed.

Voltage is applied at the source terminal starting from 0V and gradually
increasing the voltage until a spark is observed between the gap of the two
electrodes.

The voltage at which the spark is formed is referred to as the breakdown
voltage. The test is repeated 6 times and the average value is taken.
Figure 3. 12: Oil test
4. Pressure test
The insulation of the transformer are sometimes subjected to voltage greater than
its rated value. Therefore, the pressure test is carried out to test whether the
insulation of the transformer can sustain its rated voltage, as well as a higher
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Chapter 3: Nature of Training
voltage. During the test, 18 kV is applied for 2 min between MV phases and the
frame, which is earthed.
The test is successful if the breaker does not trip. Tripping indicates the flow of
leakage current, which imply that the insulation between the MV and the
transformer frame has deteriorated.
5. Load test (short circuit test)
This test is performed by short-circuiting the three LV phases and applying the
percentage impedance voltage to the primary windings. This test helps to confirm
that the secondary windings can successfully carry the full load current without
overheating. The currents flowing in the LV phases are measured using a clampon ammeter and the test is repeated for different tap positions.
6. Voltage test
For the voltage test, the secondary LV terminals are opened, while rated voltage is
applied to the primary. The secondary voltage is measured for each tap to verify
the voltage transformation.
3.6.6 The 66/22 kV substation
A Substation is an important part of power system. The continuity of supply
depends considerably upon successful operation of substations. Each substation is
fed from the generating station via incoming transmission lines and power flows via
outgoing feeders to the distribution transformers to supply consumers. Power
transformers in these major substations step down the transmission voltage to the
primary distribution voltage.
The typical layout of a 66/22 kV substation can be illustrated in figure 3.13.
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Chapter 3: Nature of Training
COMBO 66/22kV SUBSTATION
CTDS
HENRIETTA
CASE NOYALE
C571
C568
C586
C583
C569
C572
C582
C570
C573
C581
C574
C575
UNION VALE
C585
C584
C576
66kV ODD
66kV EVEN
C577
C579
C578
C580
Power
Transformer
66>22 kV
(TX CB1)
Power
Transformer
66>22 kV
(TX CB2)
B9555
B9553
B9554
22kV ODD
B9552
B9551
22kV EVEN
B9556
Local TX 1
LA PRAIRIE
B9557
Local TX 2
UNION VALE
C.CECILE/
BEL OMBRE
LE MORNE
Figure 3. 13: Layout of 66/22kV substation
The enclosed area in the figure consists of the line bay and transformer bay, which
normally consist of:
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Chapter 3: Nature of Training

Line side ABIS and Bus Bar side ABIS
It is installed to enable the technical personnel to effect isolation of part of
the network for maintenance. It provides visible isolation of part of the
network that has been switched off.

Lightning Arrester
The lightning arrester (also known as surge diverter) is the first protective
equipment that is connected at the incoming bay. It is a protective device
which conducts the high voltage surges on the transmission line to the
ground.

Circuit Breaker
A circuit breaker is a device that can open or close a circuit under normal,
as well as under fault conditions. It is designed to be operated locally or
remotely under normal conditions and automatically under fault conditions.
For the latter operation, a relay circuit is used with the circuit breaker. Oil
Circuit Breakers, which use oil as an arc quenching medium and Gas Circuit
Breakers which use Sulphur Hexafluoride (SF6) gas as medium are the
most common types of circuit breakers.

Current transformer and Potential transformer (CT and PT)
CT and PT are referred to as instrument transformers. The current and
voltage on the system are too high to be measured directly. Therefore, they
need to be stepped down into a safe and measurable value so that they can
be used in relation to protective relays and metering devices. Therefore, CT
and PT step down the high current and voltage respectively to a value
measurable and easy to handle by relays.
The 66kV transmission line enters the substation via the incoming bay where it is
fixed onto insulators and connected to the air break isolating switch known as the
line side ABIS. A set of lightning arresters is connected in parallel to the line which
provides path to ground when high voltage surges are present on the circuit.
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Chapter 3: Nature of Training
Current transformer is connected in series to the line for measuring and protection
purposes. A 66kV circuit breaker is used to open or close the circuit during fault
conditions or during maintenance and repairs. Before being connected to the 66kV
bus bar, the circuit is connected to another air break isolating switch known as the
bus bar side ABIS.
Same equipment are used on the other side of the 66kV bus bar before being
connected to the 66/22kV power transformer.
Figure 3.14 illustrates a more detailed representation of the incoming bay.
Figure 3. 14: Line diagram of incoming bay
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Chapter 3: Nature of Training
3.7 Construction and Maintenance Gang (CMG)- Production Department
3.7.1 Introduction
During my training at the Construction and Maintenance gang section, I had the
opportunity to participate in the redevelopment phase of St Louis Power Station.
3.7.2 Project Background of St Louis power station
The St Louis power station was the first diesel power station commissioned by the
CEB back in October 1955 and was operating with a generation capacity of
approximately 70MW.
However with the increase in electricity demand, the CEB undertook a major
redevelopment of the St Louis power station. It was intended to replace the older
inefficient Pielstick units with more powerful and more efficient engines.
3.7.3 Power Generation of St Louis power station
The project involved the installation and commissioning of four generating sets
(G10, G11, G12 and G13), each consisting of a Wartsila 18V46 diesel engine as
prime mover driving a three phase 11kV generator. The capacity of each generator
is 21.345 MVA.
Figure 3. 15: Electrical setup of G10 generating unit
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Chapter 3: Nature of Training
The electrical setup of the G10 generating unit is as shown in the Figure 3.15.
Electric power is generated at 11 kV by the synchronous generator. The generator
terminal is connected to 11 kV bus-bar via a circuit breaker. A Unit Auxiliary
Transformer (UAT), steps down the 11 kV to 415 V in order to supply the different
engine auxiliaries of the generating unit. The generated power is also stepped up
to 66 kV by a power transformer and is exported to the 66 kV busbar for
transmission.
3.7.4 The Wartsila 18V46 diesel engine
The prime mover is a medium speed, 4 stroke diesel engine which has a speed of
500 revolution per minute. It utilizes four piston strokes to complete one operating
cycle as shown in the figure.
Figure 3. 16: Four stroke operating cycle
1. Intake stroke
The intake stroke is also referred to as the suction stroke. For this stroke, the
piston is initially at the top of the cylinder and moves to the bottom. When the
piston is on its way to the bottom of the cylinder, the intake valve opens
simultaneously. Air enters the engine cylinder through the intake valve by a pump.
The intake valve remains open until the piston reaches the bottom end of the
cylinder. At the bottom the intake valve closes.
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Chapter 3: Nature of Training
2. Compression stroke
After the piston passes the bottom end of the cylinder it starts moving upward. At
that time, both intake and exhaust valves are closed and the cylinder is completely
sealed. This upward movement of the piston compresses the air into a small space
between the top of the piston and the cylinder head. A high temperature is
generated inside the cylinder. Fuel is then injected into the cylinder by fuel injection
pump. At the end of the compression stroke, the piston is at top end of the cylinder.
3. Power stroke
The heat of the compressed air ignites the fuel and creates a high pressure which
forces the piston down. The connecting rod which connects the piston to the
crankshaft carries this force to the crankshaft which tends to move the engine. At
the end of the power stroke the piston is at the bottom end of cylinder.
4. Exhaust stroke
When the piston reaches the bottom end of cylinder, the exhaust valves opens.
The products of the combustion of fuel are removed from the cylinder, completing
the cycle. The piston then moves to the top of the cylinder. The exhaust valve
closes. When the piston reaches the top of the cylinder the intake valve opens and
the process is continued for another cycle.
3.7.5 Excitation System
Figure 3. 17: The excitation system
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Chapter 3: Nature of Training
The Figure 3.17 illustrates the excitation system for power generation. The
Automatic Voltage Regulation (AVR) measures the generator’s terminal voltage via
a potential transformer (PT) and then determines the field current to transmit to the
exciter stator coils. When the exciter stator coils receives a direct current from the
AVR, a stationary flux is set in these coils. The exciter rotor is mounted on the
same shaft as the main rotor. The exciter rotor consists of the armature windings
which rotates. Based on the Faraday’s Law of Electromagnetic Induction, a voltage
is induced in the exciter rotor coils and the resulting alternating current is rectified
by the diode bridge into a direct current which is fed to the field winding of the main
rotor.
3.7.6 The synchronous generator
Generators are rotating machines that converts mechanical power from the prime
mover into electrical power. The synchronous generator installed at St Louis power
station has a capacity of 21.345 MVA. It consists of a rotating part known as the
rotor and a stationary part known as the stator. Synchronous generators operate
based on the principle of Faraday’s Law of Electromagnetic Induction. DC current
is applied to the rotor winding (field winding) to produce a rotor magnetic field. The
rotor is then turned by external means producing a rotating magnetic field, which
induces a three phase voltage within the stator winding (armature winding).
The rotor rotates at the same speed as the rotating magnetic field and this speed is
known as the synchronous speed and is given by:
Where,
: Synchronous speed
: Frequency
: Number of poles
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Chapter 3: Nature of Training
3.7.7 The Governor
The purpose of the governor is to control the amount of fuel injected to the engine
in order to maintain the speed at the desired level. When there is a frequency
change on the network, the governor response to this change in order to increase
or decrease the fuel injected into the engine. The governor installed at St Louis is a
digital 723 plus Woodward governor.
Figure 3. 18: The digital 723 plus Woodward governor
Therefore, the governor regulates the speed of the engine by controlling the
amount of fuel injected to the cylinders.
3.7.8 The Automatic Voltage Regulator
The Automatic Voltage Regulator (AVR) is Unitrol 1020 from ABB. It is a device
that continuously monitors the voltage of the generator and automatically initiates
corrective measures to maintain the terminal voltage of the generator. The AVR
makes sure that the synchronous generator operates within pre-set value.
AVR supplies excitation power to the field winding of the synchronous generator.
Two AVRs are operated in parallel. One is referred to as the MAIN AVR and the
other one called the REDUNDANT AVR which normally comes in operation when
the MAIN AVR fails.
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Chapter 3: Nature of Training
Main AVR
Redundant AVR
Figure 3. 19: The AVR
The output of the generator is measured using a potential transformer and fed to
the AVR. The measured value is compared with a reference or set value. The
difference between the reference voltage and the measured voltage is computed
using a differential amplifier and the error signal obtained is used by integrated
electronic modules to produce the required field current to be supplied to the
exciter stator coils as represented in the Figure 3.20 below.
Figure 3. 20: Operating function of AVR
76
Chapter 3: Nature of Training
3.7.9 The Differential Amplifier
The error signal used by the integrated electronic modules is normally generated
using a differential operational amplifier.
Figure 3. 21: The differential operational amplifier
The differential amplifier amplifies the voltage difference present on its inverting
and non-inverting inputs. By adjusting the values of the resistors
,
,
and
,
the differential amplifier is made to perform subtraction operation.
The set voltage or reference voltage is fed to the non-inverting input (+) of the op
amp and the measured voltage is fed to the inverting input (-). By using the method
of superposition, the output voltage (
) is calculated as follows:
Assumption:
(1)
=
(2) No current flows into the inverting and non-inverting terminal
77
Chapter 3: Nature of Training
Superposition method:

Make
=0 first
( )
and
from assumption 2
Therefore,
( )
= taken as zero
(
( )

Make
)
=0
=
From assumption 1,
=
. Therefore,
=
( )
( )
(
( )
) (
)
Finally,
(
)
( )
( )
(
) (
78
)
Chapter 3: Nature of Training
By making = =
output expression:
=
, the op amp gives the difference of voltage
where the voltages may be considered as:
: measured voltage
: reference or set voltage
: error
79
and
with
CHAPTER 4: PERSONAL
CONTRIBUTION
80
Chapter 4: Personal Contribution
4.1 Introduction
This chapter describes some of my personal works that I have contributed to at the
CEB.
4.2 Wind loading calculation on 14m concrete pole
During my training at the Project and Construction section, I got the opportunity to
perform site visit and inspection. While inspecting one site it was noted that two or
three poles were inclined. As a new 66kV transmission line was being implemented
along the route of Belle Vue/Sottise, the supervising engineer gave me the
assignment to assess what could have been the cause to this problem and what
could be the possible solution so that this problem do not repeat while
implementing the new 66kV line.
According to
experience acquired on site, the most possible reasons to the
problem were due to bad workmanship and the probability that the pole could not
sustain all the load imposed on it and the effect of wind load acting on the surface
on the pole. So, I proposed to perform wind loading calculation to verify if the
maximum load the pole can sustain was exceeded.
Therefore during my traineeship at the CEB, I got the opportunity to calculate the
wind loading on 14m concrete poles for 66kV overhead line. The wind acting on
the equipment that are attached to the poles are usually minor in comparison to the
wind blowing on the surface of the poles and on the conductors. Therefore while
calculating wind loading, only wind effect on pole surface and conductors will be
considered.
(1) Wind Loading on 14m concrete pole due to 366 AAAC
The most significant factor in determining the pole strength is the impact of wind on
the conductors attached to the pole.
81
Chapter 4: Personal Contribution
The total wind load is given by the formula:
F=
.................................................................... equation (4)
where,
: Force Coefficient
: Effective frontal area
q: Dynamic Pressure, given by the formula:
q=K
................................................................................. equation (5)
where,
K: Constant, 0.613
: Design wind speed, given by the formula:
:=V
.........................................................................equation (6)
where,
V: Basic wind speed
: Topography factor taken as 1 (Assume site is flat)
: Factor which takes account of:

Cables height above ground

Ground roughness and obstruction
: Statistical Factor
is taken as 1, which corresponds to a probability level of 0.63 for a period of
exposure of 50 years. It means there is only a probability of 0.63 that the basic
wind speed be exceeded at least once in a period of 50 years.
82
Chapter 4: Personal Contribution
For the calculation of the wind loading on the 14m concrete pole due to 366 AAAC,
consider figure 4.1 below which illustrates the point of fixation of conductors above
ground. Based on this figure, the wind loads of all 3 phase conductors are
calculated.
11.6m
11.3m
10.6m
9.8m
Ground
0.5m
TGL
2.4m
Figure 4. 1: Wind loading due to conductor only
Therefore,

Basic wind speed,
V = 280 km/h (Reference, Gervaise winds)
=77.78 m/s

Topography factor,
=1

Line Class,
= 0.9 (Open country with no obstruction- As
per table A1 in Appendix A)
83
Chapter 4: Personal Contribution

Statistical factor,
=1

Design wind speed,
=V
= 77.78
1
0.9
1
= 70 m/s

Dynamic pressure,
q=k
= 0.613
70
70
= 3003.7 N/

Force Coefficient,
Diameter of 366 AAAC,
D = 27.85 mm
= 0.02785 m
D = 0.02785
70
= 1.95 m/
From table A2 in Appendix A, for fine stranded cables, if D
= 0.9

Effective frontal area,
Diameter of conductor,
D = 0.02785 m
Span Length,
L = 70 m
=D L
=1.95

Wind force on one conductor,
F=
= 0.9
3003.7
= 5271 N

Now, considering figure 4.1 above,
Height of 1st phase conductor above TGL = 11.8 m
Height of 1st phase conductor above TGL = 11.1 m
84
1.95
, then
Chapter 4: Personal Contribution
Height of 1st phase conductor above TGL = 10.3 m

Equivalent load at 250mm from top =

Distance between 250mm from top to TGL = 11.85 m

Using moments with TGL as fulcrum,
(
=
)
= 14.8 kN

Wind load on all 3 phase conductors = 14.8 kN
(2) Wind Loading on 14m concrete pole alone
When calculating wind loading, it is important to know the force acting on the pole
alone. Consider figure 4.2 below.
11.6m
Hg
Ground
0.5m
TGL
2.4m
Figure 4. 2: Wind loading on pole alone
85
Chapter 4: Personal Contribution
Therefore,

Basic wind speed,
V = 280 km/h (Reference, Gervaise winds)
=77.78 m/s

Topography factor,
=1

Line Class,
= 0.95 (Open country with no obstruction- As
per table A4 in Appendix A)

Statistical factor,
=1

Design wind speed,
=V
= 77.78
1
0.95
1
= 73.89 m/s

Dynamic pressure,
q=k
= 0.613
73.89
73.89
= 3346.82 N/

Force Coefficient,
From table A3 in Appendix A,

= 1.4
Effective frontal area,
Top pole width,
a = 250 mm
Pole base width at ground level,
b = 490 mm
Height above ground exposed,
h = 11.6 m
Therefore,
= Area of trapezium
=
(
)
= 4.292

Force at center of gravity (
) of pole, F =
= 1.4
3346.82
= 20.1 kN
86
4.292
Chapter 4: Personal Contribution

Center of gravity above ground,
=
(
(
)
)
= 5.17 m

Center of gravity above TGL,

Equivalent load at 250mm from top =

Distance between 250mm from top to TGL = 11.85 m

Using moments with TGL as fulcrum,
=
(
= 5.67 m
)
= 9.62 kN
Therefore,
Total force on pole due to wind is the summation of the force due to wind on the
conductors and the force due to wind on the pole alone.
Total force obtained = 14.8 + 9.62
= 24.42 kN
The total force acting on the pole exceeds the nominal pole strength which is 21.6
kN. Therefore, the solution proposed was to reduce the effective area upon which
the wind is acting by reducing the span length and see the effect of wind loading on
the pole for span length of 60m and 50m. The results obtained were tabulated as
shown in table 4.1 below.
Table 4. 1: Calculated wind load on pole
Nominal Pole Strength
/kN
Calculated force on
Pole /kN
Span Length /m
21.6
21.6
21.6
24.42
22.32
20.12
70
60
50
87
Chapter 4: Personal Contribution
From table above it could be observed that there was a probability that the pole
could not sustain all the load acting on it. So the solution I proposed was to, if
possible, perform site inspection more regularly to verify the quality of work being
done and to reduce the span length from 70m to 50m so that the nominal pole
strength is not exceeded.
4.3 Evaluation of quotation for bimetallic lug
During my traineeship at the Technology and Procurement Section, I got the
opportunity to evaluate various quotations under the guidance of engineers. In this
chapter, I will explain about the evaluation process of a quotation for the
procurement of bimetallic lug to be used for 150 mm2 AL cable that I was assigned
to.
Following decision taken at the Store Ordering Committee, there was need to order
2500 bimetallic lugs for 150 mm2 aluminium insulated twisted medium voltage
cable. Therefore, request for quotations was sent to different bidders. Upon
receiving the bids, the quotations were evaluated both technically and financially.
4.3.1 Use of bimetallic lug
Bi-metallic Al/Cu lugs are used at the ends of aluminum conductors to allow
connection of the cable to a copper terminal. Details of such lug are as shown in
figure 4.3.
Figure 4. 3: Bi-metallic Al/Cu lug
4.3.2 Requirements sent to bidders by CEB

The bimetallic lug shall be used for the connection of 150 mm 2 aluminium
overhead insulated twisted MV cables to a copper terminal.
88
Chapter 4: Personal Contribution

The lug shall be manufactured with an aluminium barrel and effectively
friction welded onto a copper terminal.

The aluminium barrel shall be coated with grease internally.

The dimensions of the lug shall be according to EDF ref C2 AU 150 or ref
XCX-150.
Other information to be submitted by bidders:

The name of the manufacturer.

Technical brochure with photos and dimensional drawings.

Detailed breakdown of freight and insurance cost.

Country of origin of goods
4.3.3 The Evaluation Process
Only two bidders responded to the request for quotations. For the sake of
confidentiality, they will be denoted as Bidder A and B. The evaluation process will
be divided into various steps.
Step 1:
The first step in evaluating the quotation was to verify the commercial terms
stipulated by CEB to the bidders. If the quotations fail to abide by these terms, they
are rejected straightaway. Table 4.2 below illustrates the terms satisfied by the
bidders.
Table 4. 2: Compliance with conditions of purchase
89
Chapter 4: Personal Contribution
Step 2 :
A technical analysis was then performed for each criteria required by the CEB.
Table 4.3 below illustrates the technical requirements satisfied by Bidders A and B
and their technical responsiveness.
Table 4. 3: Compliance with technical requirement
Note: While evaluating the quotations it was found that bidder B did not specify
about whether the dimensions of the lug were according to EDF ref C2 AU150 or
ref XCX-150. Therefore, a query for clarification was sent to bidder B. EDF ref C2
AU150 or ref XCX-150 specifies the main characteristics of the bi-metallic lug as
well as the tests they shall comply with. After receiving the required information
from bidder B, a financial evaluation was carried out.
Step 3:
Once the technical evaluation was completed, a financial analysis was performed.
The quotations submitted by the bidders, their responsiveness and their ranks are
illustrated in table 4.4 below.
90
Chapter 4: Personal Contribution
Table 4. 4: Summary of evaluation report
Following steps 1 to 3, it can be found that bidder A was responsive both
technically and financially and having quoted the lowest price. The budget provided
was Rs 312,220. Therefore, the item was proposed for recommendation to be
procured from bidder A.
4.4 Supply to 41 housing units for NHDC morcellement at 16ème mille
When initiating the planning process of the project, the following activities were
carried out:

A preliminary survey was carried out and a site meeting was arranged with
the client to discuss about load requirement.

The type and distance of the nearest network to the proposed project was
analyzed.

A load test was carried out to determine whether the morcellement could be
supplied from an existing transformer. However, it was decided that
installation of a new transformer was required to meet the load requirement.

An electrical network design was proposed.

Cost estimate for the project was prepared and sent for approval.
4.4.1 The design process
While designing for this type of project, the following need to be taken into
consideration:

The conductors used (both MV and LV) should be of insulated type in order
to guarantee safety and respect clearances requirement inside the
morcellement.
91
Chapter 4: Personal Contribution

The service lines should not cross any other individual property.

The distribution transformer shall be located as close as possible to the
centre of load so that receiving end voltage at the far end of each distributor
is within the limit of 230 V ± 6 %.
The aim of this project was to provide an overhead electrical supply to 41 housing
units for NHDC at 16ème mille.
After the preliminary survey was conducted, it was found that supply of electricity
for this project involved:

Erection of MV network

Installation of a 22kV/415V transformer

Erection of LV network
4.4.1.1 Transformer Capacity
In order to determine the capacity of the distribution transformer to be installed, it is
assumed that the load per housing unit is 2kVA which is the ADMD (After
Diversifying Maximum Demand) value for a customer in a residential rural area. It
is the load that a customer takes after diversity factor has been taken into
consideration.
Therefore for 41 plots, the total load = 41 × 2kVA
= 82 kVA
Therefore, one (22kV/415V) 100kVA pole-mounted distribution transformer was
proposed to supply the load of 82kVA.
The percentage loading of the transformer with full load applied would be
=
× 100
= 82 %
92
Chapter 4: Personal Contribution
4.4.1.2 Cable Sizing
1. Sizing of MV cable
The primary side of the 100kVA distribution transformer is supplied from 22kV
feeder.
Apparent Power, S = √ × I × V
Primary Current,
√
= 2.62 A
Therefore, a current of 2.62 A will be flowing on the MV side. In order to be able to
carry this current, 3 × 35 mm2 torsadé conductor cable was proposed to supply the
transformer which has a current carrying capacity of 155 A at 30°C.
2. Sizing of LV torsade cable
The 100kVA transformer has an output of about 140A per phase when fully loaded.
Therefore, 3 × 70 mm2 torsade conductor cable which has a current carrying
capacity of 213A at 30°C with voltage drop of 0.87 V/A/km was proposed for the
secondary distribution.
Note: Distribution transformers are normally installed at center of load in order to
minimize voltage drop across the distributors and that voltage at far end is within
the limit required. However, for this project the client refused this proposal.
Therefore, the transformer was installed in a green space reserve and the design
proposed was as shown in figure 4.4 below.
93
Chapter 4: Personal Contribution
Figure 4. 4: Proposed design to supply 41 housing units
Other assumptions made during design process:

Load is balanced across the three phases.

Voltage drop up to LV poles only is taken. The voltage drop in the service
cables is assumed negligible.
4.4.1.3 Voltage Drop calculation
Voltage drop calculation is important so that consumers at the far end of the
distributor receives the nominal voltage of 230V with allowable deviation of ±6 %.
For my project, the design from figure 4.4 above is illustrated in a more simplified
version with consumers receiving voltage from distributors A and B.
The load current per service line will be,
= 2kVA/230V = 8.7 A per service line
Considering figure 4.5 below, voltage drop calculation is performed on distributors
A and B and the far end voltage on poles 13 and 10 are recorded.
94
Chapter 4: Personal Contribution
Proposed LV cable
Proposed service cable
Distributor A
Proposed LV Pole
27
26
98m
28
29
17m
100 kVA
16
7
17m
6
5
17m
1
39
15
2
10
38
8
17m
11
3
40
14
12
30m
13
12
33
37
36
17m
11
32
13
35
22m
6
41
34
31
25m
5
1
30
17m
2
4
7
8
17m
3
17
9
20
17m
24
35m
4
19
11
17m
5
10
9
25
21
22
23
Distributor B
Figure 4. 5: LV distribution of 100kVA transformer
4.4.1.3.1 Voltage drop calculation on Distributor A (Phase R only)
Using figure 4.5 above, the current from each service lines on each LV pole is
tabulated as shown below.
Table 4. 5: Total current on each poles of distributor A (Phase R only)
Pole Number
Current in one
service Line /A
5
6
11
12
13
Consider figure 4.6 below.
Number of service lines Total current
on pole (Phase R)
on pole /A
8.7
8.7
8.7
8.7
8.7
X
98 m
1
1
1
1
2
5
17m
r1
230V from TX
6
r2
I1
25m
8.7
8.7
8.7
8.7
17.4
11
12
r4
r3
I2
22m
I3
17m
r5
I4
Figure 4. 6: Single line diagram of LV distribution for distributor A (Phase R only)
95
13
I5
Chapter 4: Personal Contribution
Where,

r1, r2, r3, r4 and r5 are the impedances of the LV cable.

X is the start of the cable from transformer

I1 is the total current on pole 5

I2 is the total current on pole 6

I3 is the total current on pole 11

I4 is the total current on pole 12

I5 is the total current on pole 13
Current in section X-5,
= I1 + I2 +I3 + I4 + I5
= 8.7 + 8.7 + 8.7 + 8.7 + 17.4
= 52.2 A
Current in section 5-6,
= I2 + I3 + I4 + I5
= 8.7 + 8.7 +8.7 +17.4
= 43.5 A
Current in section 6-11,
= I3 + I4 + I5
= 8.7 +8.7 +17.4
= 34.8 A
Current in section 11-12,
= I4 + I5
= 8.7 +17.4
= 26.1 A
Current in section 12-13,
= I5
= 17.4 A
96
Chapter 4: Personal Contribution
The impedance per 1000m of distributor = 0.87
Impedance of section X-5, r1
= 0.87 × 0.098 = 0.08526
Impedance of section 5-6, r2
= 0.87 × 0.017 = 0.01479
Impedance of section 6-11, r3
= 0.87 × 0.025 = 0.02175
Impedance of section 11-12, r4 = 0.87 × 0.022 = 0.01914
Impedance of section 12-13, r5 = 0.87 × 0.017 = 0.01479
Therefore,
X
98 m
17m
5
52.2A
43.5A
8.7A
230V from TX
6
25m
11
22m
34.8A
8.7A
26.1A
8.7A
Figure 4. 7: Current in different sections of distributor A (Phase R only)
Voltage at Pole 5,
= Voltage at X
Voltage drop in section X-5
= 230
(
r1)
= 230
(52.2
0.08526)
= 225.55 V
Voltage at Pole 6,
= Voltage at pole 5
= 225.55
(
= 225.55
(43.5
Voltage drop in section 5-6
r2)
0.01479)
= 224.91 V
97
12
17m
13
17.4A
8.7A
17.4A
Chapter 4: Personal Contribution
Voltage at Pole 11,
= Voltage at pole 6
= 224.91
(
= 224.91
(34.8
Voltage drop in section 6-11
r3)
0.02175)
= 224.15 V
Voltage at Pole 12,
= Voltage at pole 11
= 224.15
(
= 224.15
(26.1
Voltage drop in section 11-12
r4)
0.01914)
= 223.65V
Voltage at Pole 13,
= Voltage at pole 12
Voltage drop in section 12-13
= 223.65
(
r5)
= 223.65
(17.4 0.01479)
= 223.39 V
Total voltage drop on distributor A for phase R
=(
r1)+ (
r2)+ (
r3)+ (
r4)+ (
= 4.45 + 0.643 + 0.757 + 0.5 + 0.257
= 6.607 V
Percentage voltage drop on distributor A for phase R
=
100
= 2.87 %
98
r5)
Chapter 4: Personal Contribution
It can be observed that the percentage voltage drop is less than 6%. Hence, it can
be concluded that voltage drop obtained was acceptable and that far end voltage
(voltage on pole 13, 223.39V) is within the range of 230 V ± 6 %.
The same procedures were utilized for the calculation of voltage drops in phase Y
and B for distributor A and for the phases of distributor B. The results were
tabulated as shown in table 4.6 below.
Table 4. 6: Far end voltages on distributors A and B
Distributor
Phase
Far end
Pole
Far end voltage on pole
/V
% Voltage Drop
per Phase
A
A
A
B
B
B
R
Y
B
R
Y
B
13
13
13
10
10
10
223.39
224.75
224.43
224.98
225.08
225.21
2.87
2.28
2.42
2.18
2.14
2.08
4.4.2 Cost Estimate
The cost for the supply to the Morcellement was estimated at around Rs 613,706.
The detailed estimate is given in Annex 2.
4.5 Load test and load balancing
The aim of load test is to monitor the loading of the distribution transformer and
associated networks with a view to operate at optimum efficiency and reliability.
The test is carried out when the load is expected to be at its maximum value on the
transformer. The load test is normally performed around 18hr to 19:30 P.M in the
evening on transformers supplying domestic load and during the day for industrial
loads.
The current is measured on each distributor from the transformer using a clamp on
type ammeter. Line and phase voltages were taken at:

LV switch fuse of the transformer.

The far end of the distributor to ensure voltage is within the required limit of
230 V ± 6 %.
99
Chapter 4: Personal Contribution
From the results of the load test obtained, the actions that may be taken into
consideration are:

Load balancing on the network

Increase or decrease in kVA capacity of the transformer

Installation of additional transformer
4.5.1 Load balancing at Montagne Blanche village
On 5th December 2018, I got the opportunity to assist a load test performed on a
150kVA transformer with Transformer Workshop Number 150 DX 724 situated at
Montagne Blanche. The substation has two outgoing LV feeders, one towards
Chaillet street and the other towards Boulanger street.
The load test was essential because this formed part of the maintenance works
that needed to be carried out on the network at Montagne Blanche.
4.5.1.1 Load test results for Transformer 150DX724
The load test was done at 18:15 and repeated at 18.30, 18:45 and 19.00. Figure
4.8 shows the loadings on each outgoing way at the four different times.
1. Current (A)
18:15
18:30
R
Y
B
N
Tot
KVA
R
Y
B
N
Tot
KVA
(a) Towards: Chaillet Street
52
108
80
53
240
55
75
145
87
52
307
71
(b) Towards: Boulanger Street
04
11
03
08
18
4
13
11
09
07
33
8
56
119
83
X
258
59
88
156
96
X
340
79
Feeder
Total Phase Current
Figure 4. 8: Load test results
100
Chapter 4: Personal Contribution
2. Voltage (V)
The phase and line voltages at the LV switch fuse terminals and at far end for each
phase were recorded and tabulated as shown below.
Table 4. 7: Phase and line voltages at far end
RY
YB
BR
RN
YN
BN
(a) Measured at switch fuse terminal
399
399
396
229
228
228
376
375
383
220
223
222
(b) Measured at end of line
The results illustrated that a peak load of 92 kVA occurred at 18:45 P.M. The %
load of the 150 kVA transformer is
100 = 61.3 %. At the CEB, the loading of
distribution transformer is kept around 80% in order to cater for abnormal load
conditions. If load requirements exceeds this value, increase in kVA capacity (IKC)
is normally requested. However, in our case IKC was not required. But load
balancing on each feeder was required because at the peak load, the total current
on one phase is far from being equal to the total current on the other phase, i.e.
(
)
(
)
and
(
)
.
4.5.1.2 Determination of load balancing
In order to balance load on the three phases, the number of service lines that
needs to be shifted from one phase to another are calculated.
The average current per service line was assumed to be about 5 A.
Let,
),
(
(
),
(
),
(
)
be the average currents on each phase of a distributor and
the average current of the three phases of a distributor.
101
Chapter 4: Personal Contribution
Calculation :
- Distributor towards Chaillet street
(
) =(
(
) =(
(
) =(
(
) =(
)⁄ = 77 A
)⁄ = 143 A
)⁄ = 88 A
)⁄ = 102 A
- Distributor towards Boulanger street
(
) =(
)⁄ = 11 A
(
) =(
)⁄ = 11 A
(
) =(
)⁄ = 8 A
(
) =(
)⁄ = 10 A
For distributor towards Boulanger street, the currents were almost balanced and
did not require any load shifting. However, for the distributor towards Chaillet
street, the service lines were shifted as follows:
Distributor
R /A
Y /A
B/A
Towards Chaillet Street
+25
-41
+14
Therefore,

3 service lines from Y phase to B phase

5 service lines from Y phase to R phase.
102
Chapter 4: Personal Contribution
A second load and voltage tests were performed at peak loading on the
transformer after load balancing was performed.
LV Distributor
Current ( A )
R
Y
B
N
Towards Chaillet Street
103
105
104
7
Towards Boulanger Street
13
15
14
5
Total phase current
116
122
118
X
Location
Phase Voltage ( V )
RN
YN
BN
Switch fuse terminals
233
234
234
End of LV Leg 1 (Chaillet Street)
227
226
226
It could be observed that after load balancing was performed, the voltage was
within the required limit of 230 V ± 6% and the current per phases was almost
balanced.
4.6 Earth Resistance Test
During my traineeship at the Engineering section of Curepipe, I got the opportunity
to perform an earth resistance test to assess the earth resistance of a distribution
transformer before commissioning.
4.6.1 Importance of good earth resistance
The objective of earth resistance testing is to achieve the lowest ground resistance
value possible. A good grounding system will improve the reliability of equipment
and reduce the likelihood of damage due to lightning or fault currents. If fault
currents have no path to the ground through a properly designed and maintained
grounding system, they will find unintended paths that could include people.
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Ideally, a ground should be zero ohm resistance, which practically is impossible to
achieve. However, the NEC (National Electrical Code) has stated that earth
resistance should not be more than 25 ohms.
4.6.2 Three-point (Fall-of-potential) method
The fall of potential or 3 point measurement method was used for the earth
resistance test. This method comprises of the earth electrode to be measured and
two other electrodes labelled P (potential) and C (current) as shown in figure 4.9
below.
Figure 4. 9: Fall of potential method
A current flows along the path rod1 – Soil – rod2. The potential between rod1 and
rod3 is measured by a voltmeter and the current flowing between rod1 and rod2 is
read by an ammeter. The voltmeter and ammeter are all in-built in the earth
resistance test equipment. The earth resistance R is determined through Ohm’s
law:
R=V/I
Objective:
The aim for this test was to determine the earth resistance value for a distribution
transformer before commissioning.
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Chapter 4: Personal Contribution
Apparatus used:

Megger DET4TD2

Earth rods
Procedures:
1. Before starting the test it was ensured that the system was dead and the
earth electrode under test was disconnected from the installation.
2. The electrical setup was as illustrated in figure 4.10 below.
Figure 4. 10: Test set up for earth resistance measurement
3. The megger DET4TD2 is a four terminal tester. In order to perform the 3point method, P1 and C1 terminals on the instrument were linked and
connected to the earth electrode under test. C2 is referred to as the current
reference probe (connected to rod C) and P2 the potential reference probe
(connected to rod P).
4. Rod C was driven into the earth straight out at a distance D (approximately
20m) from the electrode under test.
5. Rod P was then driven into the earth at a set number of points, roughly on a
straight line between the earth electrode and rod C. The resistance readings
were recorded for each rod P point.
6. Measurements were plotted on a curve of resistance versus distance.
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7. The correct earth resistance was read from the curve for the distance that
was roughly 62% of the total distance D.
Test results:
The test results obtained were tabulated in table 4.8 below and a graph of earth
resistance value against percentage distance of D was plotted.
Table 4. 8: Earth resistance test results
Percentage Distance D
Earth
Resistance / Ω
0
10
20
30
40
50
60
70
80
90
0
11.6
28.2
33.1
33.9
34.2
35.8
37.8
57.4
90.4
Figure 4. 11: Graph of earth resistance versus percentage distance of D
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Chapter 4: Personal Contribution
Conclusion:
From the graph obtained it could be observed that the value of earth resistance
obtained at 62% of distance D was around 36
. According to NEC, section 250-
56, the earth resistance should be less than 25
. Therefore solutions needed to
be proposed in order to reduce the earth resistance value.
Methods to improve the earth resistance value
Due to the high value of the earth resistance, different proposals needed to be
revised to improve the reading and the best practical solution was chosen. In order
to improve the earth resistance the following methods could be used:

Lengthen the earth electrode in the earth

Treat the soil

Use multiple rods
Effect of the rod size
Driving a longer rod deeper into the earth, decreases the resistance. In general,
doubling the rod length reduces resistance by about 40 percent. The curve of
figure 4.12 below shows this effect.
Figure 4. 12: Graph of earth resistance versus depth of rod
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Chapter 4: Personal Contribution
However, this solution was not possible due to the hard underlying rocks on site.
Increasing the earth electrode depth was difficult to achieve.
Treatment of the soil
Chemical treatment of soil is a good way to improve earth electrode resistance
when earth rod cannot be driven deeper because of hard underlying rock.
However, chemical treatment is not a permanent way to improve earth resistance.
The chemicals are gradually washed away by rainfall and natural drainage through
the soil. Depending upon the porosity of the soil and the amount of rainfall, the
period of replacement varies. This method was not chosen because of the high
amount of rainfall that normally occurs in the region.
Use of multiple rods
In order to improve the earth resistance value, the method of using multiple rod
was employed. When using multiple rods, they must be spaced apart further than
the length of their immersion. Referring to figure 4.13 below, if we have two rods in
parallel and a spacing of around 1.2m between the two earth rods, earth resistance
value is lowered about 35%.
Therefore for earth resistance improvement, two earth electrodes driven in the
earth in parallel were employed. The burial depth of the electrode was about 1m,
so a spacing of 1.2 m was considered. From graph, earth resistance will be
lowered about 35%. The actual reading obtained was 36
was 35% less, which was about 23.4
.
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and the expected result
Chapter 4: Personal Contribution
Figure 4. 13: Graph of % reduction in earth resistance v/s Number of rods
Therefore, using two earth electrodes in parallel and a spacing of 1.2m between
them, the same procedures described above were repeated. The reading obtained
was 24.3
which conforms to the National Electrical Code, section 250-56.
4.7 Transformer maintenance, repairs and testing
During my traineeship at the Construction and Maintenance section, I got the
opportunity to attend and assist in the maintenance and repairs of some
distribution transformers. Some of the nature of damage of the transformers that
requires maintenance and repairs are:

Oil leakages

Tap changer blocked

HV/LV windings damaged
The procedures for repairs and testing of one faulty distribution transformer is
described below.
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4.7.1 Transformer 150DX3093
In October 2018, I was following training in the transformer workshop and the
distribution transformer 150DX3093 was brought from district section for testing
and repairing. Some technical details of the transformer were:

Workshop Number: 150DX3093

Rated kVA: 150

Voltage Ratio: 22000/415V

Vector Group: Dyn11

Impedance: 4.22%
4.7.2 Preliminary tests
Before dismantling the transformer, some preliminary tests were performed.
1. Visual Inspection:
Before carrying any test the transformer was visually inspected to verify if there are
any visible damage

HT terminal: OK

LV terminal: OK

Oil level: OK

Tap changer: OK (from outside)

Oil leakage: NIL

Tank condition: Good
2. Insulation resistance test:
The insulation resistance between MV phases and frame of transformer, LV
phases and frame of the transformer and between MV and LV phases were
measured. The results were tabulated as shown below.
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Chapter 4: Personal Contribution
Table 4. 9: Insulation resistance test before repair
Tests
MV phases & Frame
LV phases & Frame
MV phases &LV phases
Test Results
/Ω
>500M
>500M
>500M
Expected
Results / Ω
Infinity
Infinity
Infinity
3. Transformer Turns Ratio (TTR):
A TTR test was performed to measure the turn ratio of the high voltage and low
voltage windings of each phase of the transformer and to detect faults in the
windings. It was found that the TTR handle was hard to rotate. Possible causes
included a faulty tap changer or open circuited MV/LV windings.
4.7.3 Dismantling, Repairs and Testing
The core assembly was removed from the tank in order to verify for any damage. It
was observed that the MV coil of phase Y was burnt and broken. The possible
reasons could have been surges due to lightning strikes or severe overloading.
The transformer oil was contaminated with carbon and the paper insulation was
burnt. I got the opportunity to assist in the reparation works of the transformer.
The transformer oil was fed to the oil filtration plant in order to remove the
presence of carbon. The top part of the laminated core was removed first and the
windings of phase Y were removed as shown in figure below.
Figure 4. 14: Dismantling and repairing of distribution transformer
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The transformer workshop is no longer involved in the rewinding process and thus,
windings from another transformer (no longer in use) of same make, model and
rating but which had one phase in good condition were used. After replacement of
the windings, the laminations were put back and the core assembly mounted inside
the tank again. A series of tests were then performed to assess the proper
operation of the transformer.
1. TTR test
The TTR test was again carried out but this time to ensure that:

Whether the tap changer connections have correctly been made

Whether there is a short circuit between the phases.
The results obtained were tabulated in table 4.10 below.
Table 4. 10: TTR test after repair
Tap
Position
MV /V
1
2
3
4
5
23100
22550
22000
21450
20900
LV /V
239.6
Expected
Ratio
96.41
94.12
91.92
89.52
87.23
Measured Ratio
AB
BC
CA
96.44
96.14
91.84
89.54
87.25
96.46
94.16
91.88
89.57
87.24
96.38
94.10
91.90
89.48
87.20
2. Dielectric test of oil
A sample of oil from oil filtration plant was taken and tested as shown in figure 4.15
below.
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Chapter 4: Personal Contribution
Figure 4. 15: Testing of oil sample
One terminal of the test jar was connected to a source of supply and the other
terminal was earthed as shown in figure. Voltage was applied at the source
terminal starting from 0V and gradually increasing the voltage until a spark was
observed. The voltage was recorded and the test was repeated 5 times and the
average value was taken.
Table 4. 11: Oil test results
Tests
Test Results
/ kV
Average result
/kV
1
36
2
37
37.6
3
40
4
38
5
37
The results obtained showed that the transformer oil has good insulating properties
and can withstand the normal operating voltage of the transformer.
3. Pressure test
This test was meant to verify if the insulation of the transformer can sustain its
rated voltage. 18kV was applied between the MV terminals and the frame of the
transformer for 2 minutes. The test was successful as the circuit breaker did not
trip due to low leakage current flowing. This therefore implies that the insulation
between the MV and the transformer frame was good.
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4. Voltage test (No load)
22kV was applied between the phases of the primary of the transformer. The
secondary LV terminals were opened and secondary voltage was measured to
check the voltage transformation for each tap position. The results obtained were
tabulated as shown in table 4.12.
Table 4. 12: Voltage test result
Phase
Tap Position and Voltage/V
Red/Yellow
Yellow/Blue
Red/Blue
Red/Neutral
Yellow/Neutral
Blue/Neutral
1
2
3
4
5
380
380
380
220
220
220
390
390
390
225
225
225
400
400
400
230
230
230
410
410
410
235
235
235
420
420
420
240
240
240
5. Load test
The LV phases of the transformer were short circuited and 4% of the primary
voltage was applied between primary phases. The percentage impedance of the
transformer was 4.22% but the test was carried out at 4% since test facilities
available was at 3%, 4% and 5%. The current flowing in the LV phases were
measured and the test was repeated for the different tap position shown in table
4.13.
Table 4. 13: Load test results
Current /A
Red Phase current
Yellow phase current
Blue Phase current
Tap Position
1
3
5
182
180
180
192
189
189
202
200
197
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The full load current of the transformer is calculated as:
=
√
=
= 208 V
√
The transformer has rated impedance voltage of 4.22%. However, since only 4%
impedance voltage (880 V) was applied on the transformer MV windings, the short
circuit current obtained was less than that calculated for full load current.
Following repairs and successful testing, the transformer was ready to be sent to
the district concerned.
4.8 Underground design for new Belle-Vue/Sottise 66kV transmission line
The CEB had embarked on the construction of a second 66kV transmission line
from Belle-Vue to Sottise, so as to be able to maintain reliability and security of
supply in the Sottise and Grand Bay region. Part of this 66kV line was proposed to
be underground for its entry in CEB substation at Belle-Vue. At the project and
construction section, I got the opportunity to carry out cable sizing, to design
trenches and follow up the implementation of the line.
The procedures were as listed below:
1. Perform a preliminary survey
A preliminary survey was carried out to identify the possible routes for the
proposed network. After analyzing different possibilities, the best line routing was
selected.
2. Initiate wayleave procedures
Part of the underground network was along Terra Sugar Estate with a road cross
on Plaine des Papaye road near Belle Vue substation. Therefore, wayleave had to
be obtained from Terra Sugar Estate and the Road Development Authority (RDA).
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Chapter 4: Personal Contribution
3. Cable sizing
Manufacturers provide standard current ratings for their cables for standard
conditions. Derating factors (correction values) are also provided to allow the
current to be corrected for different site conditions.
Derating factors are provided for variation of:

Ground temperature

Thermal resistivity of the soil

Spacing between groups of cables

Depth of laying
The maximum power that shall be transmitted along the line was 75MVA.
Therefore, the current carrying capacity required for the cable can be calculated
as:
I=
√
= 656 A
Taking into consideration the derating factors so as to correct current for the site
condition, the current carrying capacity of the cable is:
From manufacturer's catalog (Appendix B):

Ground temperature, 25° C = 0.93

Thermal resistivity of soil, 1.2km/W = 0.92

Depth of laying, 1200mm = 0.97
According to manufacturer, the current carrying capacity for 630mm2 66kV XLPE
copper cables laid in air has a current carrying capacity of 840A. Therefore,
Icorrected = 840
0.93
0.92
0.97
= 697 A
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After applying derating factors, it can be observed that the current carrying capacity
of 630mm2 66kV copper cable is 697 A, which is more than sufficient to carry the
required power. Therefore, the 630mm2 XLPE copper cable was selected. Its
current carrying capacity makes it possible to transmit more power in case there
are future development in the region.
4. Trench design
(i) Direct laying in ground
Part of the underground network was along the Terra sugar state. For this portion,
the 66kV transmission line was directly buried in ground. The trench depth was
1200mm. The single circuit 66kV cables was laid and trench was backfilled with
compacted rocksand. Warning slabs were then placed for safety precautions. The
trench was then filled with compacted loose soil. Warning tapes were placed at
150mm from top of trench to indicate that the area contains CEB underground
cables. The trench design for direct laying is as illustrated in figure 4.16 below.
150
Ground Level
Warning Tapes
650
Compacted
Loose Soil
1200
Concrete Warning Slabs
2 PVC- Optic
Compacted
Rocksand
550
63mm
150
UG Cables
800
Figure 4. 16: Trench design along Terra Sugar Estate
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Chapter 4: Personal Contribution
(ii) Laying in pipes for road cross
A portion of the underground network was across the road near Belle Vue
substation. For this section of road cross, the cables were placed in pipes and
trench backfilled with concrete. During the trench design, additional pipes were
placed for another single 66kV circuit and for 22kV circuits. These were placed in
order to cater for future developments in the region and hence avoiding excavating
the road again. Warning slabs were then placed and covered with crusher run.
Warning tapes were then placed and a layer of bituminous concrete was used. The
trench design is illustrated as shown in figure 4.17 below.
120
Bituminous concrete surface
770
Warning Tapes
1500
Compacted
Crusher run
63
100
Concrete Warning Slabs
Concrete
Jacket
50 160
30
160
47
2 PVC- Optic
63mm
610
160mm PVC pipes
100 160 30 160
150
160 30 160
550
160 30 160 100
1900
Figure 4. 17: Trench design across road
5. Follow up works
Figure 4.18 illustrates the work progress of the implementation of the underground
network.
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Chapter 4: Personal Contribution
Figure 4. 18: Follow up works for Belle Vue/Sottise project
The main problems that were encountered on site were the presence of a water
pipe and telecom underground pipes along the proposed line route. Therefore,
care had to be taken while digging the trench. Normally, CEB underground cables
should have a minimum clearance of 500mm from any other services and is
always placed below the other services.
Before carrying any work on site, a letter was sent to the police commissioner to
request the assistance of a police officer on site in order to ensure road safety and
allow smooth road traffic since the laying of cables on the road cross was done in
two steps. The road was a two way traffic and hence, in order to not interrupt the
traffic, excavation of the trench was done on one lane first. The pipes were laid and
was covered with concrete. The trench was then backfilled with crusher run and a
layer of bituminous concrete was placed on top. Afterwards, the second lane was
excavated and the step was repeated.
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4.9 Additional Design
4.9.1 Type of bonding for the UG cable
Bonding is the term used to indicate connection of the cable metallic sheath to
earth.
When the conductor carries an alternating current, the current induces a voltage in
the sheath known as the sheath voltage. This induced voltage depends on:

The inductance between core and sheath

The conductor current

The length of the cable
When the sheath of the single core cable is bonded to earth or to other sheaths at
more than one point, a current (circulating current) flows in the sheath due to the
emf induced by the ac conductor current. It is important to limit the sheath voltage
to an acceptable level (65 V/km) in order to avoid electric shock. The voltage is
maximum at the farthest point from the ground bond. Also, it is required to reduce
the circulating current in the sheath due to its undesirable effects.
For the purpose of minimizing the sheath current and voltage, methods of bonding
is used. At the CEB the three methods used are:

Single point bonding

Mid-point bonding

Cross- bonding
Depending of the length of the cable routing, the appropriate methods are used.
Sheath bonding or grounding must perform the following operations:

Limit sheath voltage

Reduce or eliminate sheath losses by reducing circulating current
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The voltage induced in the sheath is given by:
V/m
Where,
: conductor current (A)
:2
M
(
)
The mutual inductance M between conductor and sheath is given by:
M = 0.2
(
)
(mH/km)
Where,
S : Axial spacing between cables
: Mean diameter of sheath/screen
The details for the 630mm2 UG cable is obtained from the manufacturer’s catalog
and is as listed below:
Overall diameter of cable: 85.3 mm
Conductor diameter: 30.4 mm
Conductor screen: 1.0 mm
XLPE: 9.1 mm
XLPE screen: 0.9 mm
Copper wire/Tape: 0.1 mm
Therefore, using the details given above, the mutual inductance, M, is calculated:
S = 85.3 mm
D = (30.4 + (2 x (1.0+9.1+0.9+0.1)) = 52.5 mm
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(
M = 0.2
= 2 x 10-7
)
(mH/km)
(
)
= 2.357 x 10-7 H/m
=2
M
(
)
= 2 × π × 50 × ( 2.357 x 10-7)
= 0.00007404
The induced sheath voltage,
V/m
= 656 × 0.00007404
= 0.04858 V/m
The length of the underground cable was 275 m.
Therefore, the sheath voltage induced for the cable run of 275m:
( )
V
= 13.4 V
The induced sheath voltage is 13.4 V, which is well below the acceptable limit (65
V). Therefore, single point bonding is required.
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4.9.2 Sag calculation to determine clearance for Metro Express project at St
Louis power station
Problem Analysis:
In the context of implementing the light rail project in Mauritius, I got the opportunity
to attend meeting held with Larsen and Toubro (L&T) contractors in order to
discuss the consequences the project is imposing on the transmission network.
One major problem that needed to be taken into consideration was the vertical
clearance from the last span of the St Louis-Ebene 66 kV overhead transmission
line. It was suspected that due to the height of the railway track in that region, there
would not be the minimum required clearance that need to be respected. The
situation is as represented in the Figure 4.19 below.
Figure 4. 19: Clearance for Metro Express project
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Chapter 4: Personal Contribution
From the figure, it could be observed that the railway track was passing just below
the lowest conductor. Therefore, it was necessary to perform sag calculation in
order to verify if there would be the minimum required clearance between the
lowest conductor and the train.
Survey Results
Due to the major importance of the project, a geographical survey was conducted
by the CEB land surveyor so as to obtain the required parameters to perform the
calculations. The result obtained from the survey is as represented in the figure
below.
Figure 4. 20: Survey results
G
, G
and G
are the heights above mean sea level. They represent the
elevation (on the ground) where tower 1, railway track and tower 2 are situated
respectively with respect to the mean sea level (MSL). The MSL is the datum (a
fixed starting point of a scale) for measurement of elevation and altitude.
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Chapter 4: Personal Contribution
Sag calculation
Sag is the difference in level between the point of support and the lowest point on
the conductor.
Conductor sag should be kept to a reasonable value in order to reduce conductor
material and to respect the minimum required clearance to ground. It also provide
a safe tension to the cables to prevent them to be too stretched and break.
From Figure 4.20 above, the smallest value of ground level, G , was taken as
reference and this value was subtracted from the other ground level values. The
differences were then added to their respective values of height so that all
calculations and results obtained would be based on a common ground (reference)
level.
Figure 4. 21: Sag calculation
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From Figure 4.21 above, the conductor is suspended between points of support A
and B at different level represented by the slope. The conductor used is ASTER
366 having the following information.
ASTER 366 conductor
Properties
Value
Weight (kg/km)
1009
Ultimate Tensile Strength (UTS)/ kN
115.35
Safety factor
10
The lowest point on the conductor is at a distance of
m from point of support A.
m is the distance between lowest point on conductor and point of support B and
m is the distance from lowest point on conductor to the 9m pole on the railway
track.
The span length i.e. the length between points of support A and B was 244.63 m.
Therefore,
Weight of conductor/ meter run, W = 1009/1000 = 1.009 kg
Working tension, T =
=
= 1176 kg
…………………………………………………….. (i)
Sag,
=
(
)
and Sag,
( )
( )
(
)(
=
(
)
)
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Using equation (i),
(
(
(
)
)
)
…………………………………………….................(ii)
Solving equation (i) and equation (ii), we get
and
h = (19.12-18.9)+3.97= 4.19 m
= 102.35 m
Having found
Therefore,
=
, the value of
(
)
=
can easily be found:
(
)
= 4.49 m
The vertical clearance of the lowest point on the conductor from ground is then:
=Height of point of support A -
-y
= 18.90-4.49-y
=14.41-y
The value of ‘y’ is obtained by finding the angle of the slope ‘θ’.
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Chapter 4: Personal Contribution
θ=
) = 0.93⁰
(
Thus, tan θ =
( )= tan (0.93)× 102.35 = 1.66 m
The vertical clearance of lowest point to ground = 18.90-4.49-1.66
= 12.75 m
The lowest point on the conductor was found to be at a distance of
9m pole on the railway track. By finding the value of
m from the
m, the sag
was
calculated.
= 6.91 m
=
(
)
=
(
)
= 0.02 m
Therefore, the maximum height of the conductor to ground at the railway track
would be:
= Height of lowest point on conductor to ground +
+ (y-1.55)
= 12.75 + 0.02 + (1.66-1.55)
=12.88 m
The vertical clearance from the conductor to the top of the 9m pole would then be:
= 12.88 – railway height – 9m height of pole
= 12.88 – 8.65 – 9
= -4.77 m
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Chapter 4: Personal Contribution
Conclusion
From the result obtained, it could be observed that the 66kV overhead
transmission line would be 4.77m below the 9m pole, which is not acceptable.
According to the Electricity regulation in Mauritius, the minimum distances from any
building or structure to any position to which a conductor in an overhead line may
swing under the influence of wind shall be as specified below.
Nominal Voltages
Not exceeding 1000 V (bare conductors)
Clearance
Distance
Distance
Radius
(vertical)
(Horizontal)
4.0 m
4.0 m
4.0 m
2.0 m
0.5 m
4.0 m
4.0 m
2.0 m
0.5 m
4.0 m
4.0 m
2.0 m
0.5 m
4.6 m
4.6 m
4.0 m
7.5 m
7.5 m
7.5 m
7.5 m
7.5 m
7.5 m
( Insulated)
Exceeding 1000V but not exceeding 11kV (bare)
4.0 m
( Insulated)
Exceeding 11kV but not exceeding 33kV (bare)
4.0 m
( Insulated)
Exceeding 33kV but not exceeding 132kV(pole 14m)
( Tower)
Exceeding 132kV but not exceeding 220kV (Tower)
Solution
The solution proposed was to remove the existing tower 1 at St Louis power station
and implement a new tower just before the railway track with the required
clearances. Part of the line for the new proposed tower was also required to be
underground to be fed to the 66 kV bus-bar inside the power station.
The work was planned according to the Gantt chart below.
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The figure below illustrates the work implementation on site.
Figure 4. 22: Work implementation on site
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CHAPTER 5: ANALYTICAL TOOLS
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Chapter 5: Analytical Tools
5.1 Introduction
During my training at the CEB, I had been exposed to a number of test tools and
measuring equipment which I have deemed important to elaborate in this chapter.
5.2 Measuring and Testing Instrument
These instrument are used for taking measurements during pre-commissioning
tests on new equipment and cables, test for trouble-shooting and fault finding or to
test status of line and equipment. Some of the measuring and testing equipment
used at the CEB are:
1. Line Voltage Detector
The line voltage tester is used to ensure that the 22kV line is de-energised before
any work or intervention need to be carried out on the network by the technical
staffs. The tester consists of a normally open relay which is energised when the
line tester is in contact with a live conductor. The relay then closes a circuit
containing a dc battery, a buzzer and a light emitter and the sound and light
emitted indicate that the line is alive.
2. Digital Multi-meter
The digital multi-meter is used to measure electrical quantities such as resistance,
alternating and direct current and voltages, capacitance etc. Each quantity has a
different full scale range provided in the meter.
It is useful as a trouble shooting equipment for carrying out continuity test. The
continuity test is carried out using the ohm mode or by using the buzzer mode to
ascertain continuity through its beeping sound.
3. Oil Dielectric test set (Megger OTS80PB)
This oil tester set measures the electric breakdown strength of both new and used
oil in transformers. It is fully automatic with all test standards built into the unit. All
the operator needs to do is to load the oil sample into a test jar and press the start
button and record the results after every time interval set.
132
Chapter 5: Analytical Tools
4. Transformer Turn Ratio (TTR) test set
The TTR test set simply verifies the turns ratio between the primary and secondary
windings of a distribution transformer. The transformer turn ratio is given by
where,
is the number of turns in the primary winding
and
is the number of turns in the secondary winding
.
5. Earth Resistance Test Set (Megger DET4TD2)
Megger's DET4TD2 is an enhanced earth loop tester that is capable of performing
2, 3 and 4 point testing with selectable 25V or 50V output. This earth tester also
automatically evaluates and displays the connection and condition of any
connected P and C spikes, showcasing the results on the built-in LCD screen. The
instrument is able to measure earth resistance from 0.01
to 20k .
5.3 Software Application
Software application like Microsoft Word, Excel and Visio have been a very helpful
tool in the realisation of a large number of engineering tasks. It has been used for
various works such as performing engineering design works of network,
administrative works, monitoring of works, report writing and so on.
At the CEB, the SAP (System, Application and Product in Data Processing)
software is a vital program which is applicable in almost every tasks of the CEB
such as doing purchase requisition, monitoring of stock level of materials,
preparing estimates for projects and so on.
133
CHAPTER 6: CONCLUSION
134
Chapter 6: Conclusion
During my two years of pre-registration training at the Central Electricity Board, I
have been able to acquire knowledge and skills in the field of electrical engineering
and also gain experience in the field of work. This has been a very enriching
experience both on professional level and also as a human being.
At the CEB, the concept of engineering learnt from the University is of great
importance and is applicable in many of the different sections. I have participated
in various engineering activities ranging from site visits, design of HT and LV
networks, applying engineering knowledge to locate faults, evaluation of bidding
documents, site supervision and inspection of network, project management and
others.
Moreover, we never stop learning. As an engineer, we have to continuously keep
track on new findings and research so as to improve our knowledge and skills and
gain further experience to better serve the profession.
Finally from my training, I believe that I have acquired enough knowledge and
experience, as so to be proficient and have a better approach towards the role and
code of ethics of a full-fledged professional Engineer.
135
CHAPTER 7: SUMMARY OF
STATEMENT OF COMPETENCIES
136
Chapter 7: Summary of Statement of Competencies
137
Chapter 7: Summary of Statement of Competencies
138
Chapter 7: Summary of Statement of Competencies
139
Chapter 7: Summary of Statement of Competencies
140
Chapter 7: Summary of Statement of Competencies
141
Chapter 7: Summary of Statement of Competencies
142
APPENDIX A
143
Appendix A
Table A 1: Factor S2 for class C (Overhead line)
H (m)
(1) Open
country with
no
obstructions
(2) Open country
with scattered
windbreaks
(3) Country with
many windbreaks;
small towns;
outskirts of large
cities
(4) Surface with
large and frequent
obstructions, e.g.
city centres
3 or less
5
10
0.73
0.78
0.90
0.63
0.70
0.83
0.55
0.60
0.69
0.47
0.50
0.58
15
20
30
0.94
0.96
1.00
0.91
0.94
0.98
0.78
0.85
0.92
0.64
0.70
0.79
40
50
60
1.03
1.06
1.08
1.01
1.04
1.06
0.96
1.00
1.02
0.89
0.94
0.98
H= Height of conductors above ground
Table A 2: Force coefficient Cf for conductors
Force coefficient Cf
Flow regime
D.Vs < 0.6 m²/sec
subcritical flow
D.Vs  0.6 m²/sec
supercritical flow
Smooth surface
1.2
0.5
Fine stranded cables
1.2
0.9
Thick stranded cables
1.3
1.1
Type of surface
144
Appendix A
Table A 3: Force Coefficient on reinforced concrete pole
145
Appendix A
Table A 4: Factor S2 for class B (pole h<50m)
H (m)
(1) Open country
with no
obstructions
(2) Open country
with scattered
windbreaks
(3) Country with
many windbreaks;
small towns;
outskirts of large
cities
(4) Surface with
large and frequent
obstructions, e.g.
city centres
3 or less
5
10
0.78
0.83
0.95
0.67
0.74
0.88
0.60
0.65
0.74
0.52
0.55
0.62
15
20
30
0.99
1.01
1.05
0.95
0.98
1.03
0.83
0.90
0.97
0.69
0.75
0.85
40
50
1.08
1.10
1.06
1.08
1.01
1.04
0.93
0.98
146
APPENDIX B
147
Appendix B
148
REFERENCES
149
References
REFERENCES

Distribution System Study: Construction Manual. Tractabel (December
2001).

Mehta V.K and Mehta Revised edition. "Principles of Power System", S.
Chand & Co. Ltd, New Delhi.

B.R.GUPTA, 2006. "Power System Analysis and Design". S. Chand & Co.
Ltd, New Delhi.

U.A.Bakshi and M.V.Bakshi, 2014. "Electrical Machines I & II". Repro India
Ltd, Mumbai.
150
ANNEX 1: TRAINING RECORD
BOOK
151
ANNEX 2
152