Notes for ADDC HV Competency
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Updated: 28.10.2015
INDEX
Definitions
1- MV Cable
1.1- Type of MV cables
1.2- Construction & Parts of Cable
1.3- Trench, Laying, & dressing of MV Cable
1.4- Tiles & Warning tape for MV cable
2- Cable Joints
2.1- Types of Joints
2.2- Construction & Parts of Joints
3- Cable Terminations
3.1- Types of Terminations
3.2- Construction & Parts of Terminations
3.3- Cable Glands
4- Earthing
4.1- Earthing of equipment
4.2- Earthing of Substations
5- Substations
5.1- Private substation
5.2- ADDC substation
5.3- Switching station
5.3- Primary
6- Switchgear
6.1- Panel Switchgear
6.2- RMU
6.3- Package Unit
6.4- Operation
7- Testing
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Definitions
LAP (Limited Access Permit)
A permit document which defines the limits within which work may be carried out on or near the system
and specifies the necessary safety precautions.
PTW (Permit to Work)
Equipment is isolated (off & earthed) Earth cannot be removed during the work.
PTW specifies the equipment, point of isolation, positions of primary earth and additional earth and
actions to be taken.
SFT (Sanction for Test)
A permit document which specifies the equipment, points of isolation, positions of the earth, tests to be
carried out which requires the removal of primary earth and actions to be taken.
Open Point:
A Point where the circuit and busbar both are live but the CB is off.
An open CB where source and the cable both are live.
Point of Isolation
A point where electrical separation is done from the rest of the system for safe maintenance works.
Circuit & Busbar both are off, earthed and tagged.
An Interlock is a feature that makes the state of two mechanisms or functions mutually
dependent. It may be used to prevent undesired states in a finite-state machine, and may
consist of any electrical, electronic, or mechanical devices or systems.
FO Field Operation Officer
FS Feeder Switch
CR Central Region
TOP Temporary Open Point
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Working in vicinity of ADDC Asset “buried underground Services (Electrical Cable /Water
Pipeline)” within three meters or exposing the services
Contractors working in vicinity of ADDC Asset within three meters, or exposing existing
services shall not start the work until verifying and complying with the followings: (Refer to
flow chart # 3 (Appendix IV):
5.1.2.1 Contractor shall initiate the NOI or R-NOI process by sending a formal letter to
AMD as per AMD NOI Process,
5.1.2.2 Contractor shall receive and review details of ADDC’s services in the vicinity of
their work, including this guideline;
5.1.2.3 The contractor shall appoint an approved CCP with scope of work matching the
work to be performed, or can nominate a CLP to ADDC HSEQ Dept. for processing
a CCP approval;
5.1.2.4 The CCP shall prepare and submit a method statement clearly explaining the
methodology of the work, not limited to, but also including equipment, staff and
their competency i.e. the qualification of equipment operators, equipment
conditions, method of protections of the services, and relocation methodology
where required;
5.1.2.5 A risk assessment shall be conducted using ADDC assessment criteria (guidance
including the forms are provided below in Appendix II), the assessment shall
cover all the work activities as required, and be conducted by a qualified HSE
Engineer;
5.1.2.6 Method statement and risk assessment shall be submitted and approved by
concerned ADDC business unit (Projects, EMD, WO&MD and / or HSEQ Dept.);
5.1.2.7 Approval of MoS and RA represents no objection to start Safety Document
Process subject to compliance with the followings conditions and ADDC SSR;
5.1.2.8 The contractor’s Competent person CCP shall apply for the safety document
(LAP/PTW) using appropriate request form, this should be approved by Projects
or EMD or WO&MD (who is applicable) and submitted to Network Management
Division / Planning for further processing;
5.1.2.9 Upon final approval, The CCP will be informed by network planning to collect the
safety document (LAP/PTW) from NMD/EMD/WO&M Authorized Person in the
area where the work is to be carried out;
5.1.2.10 Contractor shall Start work on site under direct full time supervision of the CCP
(safety document holder);
5.1.2.11 Contractor shall adhere to All occupational health and safety measures
mentioned in MoS and Safety Documents, and in case of where any violation of
applicable requirements is identified , the work will be suspended and
appropriate action will be taken against the contractor (under the Law 10/1976)
5.1.2.12 In the case where an emergency situation may arise (i.e. cable damage and / or
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injury etc.) work should immediately stop, , all workers should evacuate the area
to a designated safe place, DCC “Distribution Control Centre (Tel.02 44 603 42)
should be called and no person shall approach the affected cable; and
5.1.2.13 In case of an injury or fatality occurs Police Dept. (999) shall immediately be
called.
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MV Cable
1.1- Type of MV cables
1.2- Construction & Parts of Cable
Conductor
Carries the load current
Semiconductor - Conductor Screen
It provides smooth & void free interface with insulation.
XLPE Insulation
1- Prevents flow of electricity from conductor to ground or in other conductors
2- Withstands the electrical stress produced by the alternating voltage.
3-
3.3- Cable Glands
Both the BW and CW glands are provided with shrouds, lock nuts and earth tags as standard. They are
both also available is an ordinary PVC version or as an LSNH (Low Smoke Non Halogen) version
depending upon the cable being terminated to. The following sizes 20S, 20, 25 and 32 contain 2 glands,
2 shrouds, 2 locknuts and 2 earth tags. The following sizes 40, 50, 63 and 70 contain 1 gland, 1 shrouds,
1 locknut and 1 earth tags.
BW Gland - Brass gland for use with steel wire armoured cables (H694-XL). Used to provide clamping of
the armour wire to ensure electrical continuity and mechanical retention of the cable. The BW gland is
used for indoor application when a waterproof seal is not required.
CW Gland - Brass gland for use with steel wire armoured cables (H694-XL). Used to provide clamping of
the armour wire to ensure electrical continuity and mechanical retention of the cable. The CW type
gland is used for outdoor applications and where necessary to provide an IP66 seal with the outer
sheath of the cable.
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5. Substation
5.1- Typical Private Substation
A typical substation is the one which has a HV switchgear, step down transformer (11/0.415kV) and LV
switchgear.
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5.2 ADDC Substation
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5.3- Switching station
A switching station on the other hand is only having 11kV switchgears for providing 11kV ring circuits
when required. A circuit starting from a Primary feeds all the 11/0.415kV 6-7 substations and may come
in switching station.
For every switching station there is an express feeder which connects switching station with the
primary, remains open all the time.
If a shutdown is to be taken at a substation, it is isolated from the network from both ends. The circuit is
completed from the other side.
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6- Classifications of Switchgear
6.1- Panel Switchgear
Comprising of cubicles with the following parts:
1.
2.
3.
4.
LV/Control Supply
Bus bar
CB
Cable compartment
CB types:
1. Fix
2. Withdrawable types
Fix:
1. Vacuum
2. SF6
Withdrawbale type
1. Oil Type
2. Vacuum
3. SF6
6.2- RMU (Ring Main Unit)
1. QRM (SF6 630A Feeder Switch + 250A Tr Switch with O/c & E/F protection)
2. TRM (SF6 630A Feeder Switch + 250A Tr Switch with O/c & E/F protection)
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QRM:
1. 2f+2t
2. 3f+1t
3. 4f
TRM
1. 2f+1t
2. 3f
Application of QRM 3f+1t could be where client may have a special requirement of 3 feeders like one
express feeder from primary.
Application of QRM 4f is where ADDC don’t have spare feeder available in switching station switchgear.
6.3- PU (Package Unit)
A compact type of substation comprising of a transformer, TRM/QRM and LV panel.
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6.4 Operation of Switchgear
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Point of Isolation:
If you have to work on a substation which is between two substations, you need to isolate it on both
ends. Find the side where you have a withdrawable type CB. ADDC Night duty staff will feed the rest of
the circuit from the other end and operation dept. will do the operation;
1.
2.
3.
4.
5.
Check the panel that the circuit is open
Rack out the CB,
Go to the other end and turn off the switch (in case of a TRM, QRM)
Apply earth
Lock out tag out
Come back to the first substation Switchgear and apply earth, For Earthing, perform as following:
1.
2.
3.
4.
Lock out and tag out the busbar shutter.
Open the circuit shutter (cable side)
Check with 11KV cable tester and discharge.
Apply Portable earth
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Important!
If you have been given an open point, always withdraw the CB at point-1. Because if you turn off the CB
switch on the point-2 , apply earth and then you come back and try to withdraw the CB, It may close due
to the shock or mechanical fault or by electronic mean , resulting in huge flashover.
Q.1 What are the Isolator Points when a cable is between PRY & SWS and your
substation is between them. Tell Shutter Names ?
Q.2 Position of Switches when earth is not applied and shutdown is in progress.
Q.3 Tr.-2 is to be replaced, tell the isolation & LOTO points in Fig. 2.
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Q.4 The cable has to be replaced between Tr.2 & MDB-2, Tell the Isolation &
LOTO points In Fig.2
Q.5 A Panel is to be added in SWS, where’ll you request for shutdown and ISO &
LOTO points?
Questions For Cables
1- What is main directive factor to be considered while planning underground
cable installation?
2- State the procedure to test and commission a new MV Cable
3- Why AC 0.1 Hz VLF is preferred over AC service frequency test
4- Why DC is damaging the XLPE insulation of cables
5- State possible causes of failure of power cables
1- What are the factors to be considered for selecting MV cables
2- What are the tests to be done while installing MV Cables
3- What are the factors affecting on degrading of MV Cables
4- What is the minimum bending radius of following cables:
a)- MV 3C unarmoured Cable
b)- MV 3C armoured Cable
c)- MV 1C unarmoured Cable
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d)- MV 1C armoured Cable
5- What are the bonds available for MV cables
6- What are the causes of cable faults (including cable installation mistakes)
7- What are the isolation points for various swgr to be replaced
8- what is the procedure to connect a cable inside substation (Ds) & primary
(plugin type)
9- What is voltage drop
10- How voltage drop occurs & affects cable
Questions For Switchgear
1- What are the various types of HV swgr (manufacturer / model)
2- Explain the process of installation of swgr
3- What is the value of torque to be set while tightening the bolts of busbar in a
swgr.
4- What are the various types of test to be done before commissioning a swgr.
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