Operation & Maintenance Manual
18
COMMISSIONING
handle on the front door panel to OFF or ON or remotely switch
the breaker. The status of the device can be checked with the
indicators located at the front door.
6.4.4 - Earthing of Bus and Switches
An interlock allows the bus to be earthed when all the feeder
switches are disconnected from the bus (Dead Bus Check).
This is to ensure the respective bus is dead before earthing.
Motorised version of the earth switch is provided as standard
package.
Before earthing operation switch the local remote switch to local
mode.
Do not trip the breaker electrically when disconnector
switch is in earth position.
Any special interlocks for earthing operations will be shown in
the technical project drawings.
6.5 - Safety interlocks in GIS Switchgears
Following Interlocks are provided in GIS switchgear for safety
purpose during operation & maintenance :-
1. Mechanical & Electrical interlocks prevent the operation of
disconnector switch, when the breaker is ON.
2. Disconnector switch can be operated only when VCB is off.
3. Closure of VCB is not possible when the disconnector switch
is in operation.
1. VCB / Disconnector Switch
Isolator can be operated only when VCB is in OFF
condition. The selector position is padlockable.
VCB can t be operated, either mechanically or electrically,
when Isolator is accessed.
2. Permissive Earth
Feeder: Bus Coupler & Riser
Premissive Earth (PE)
1. In normal condition key will not be available in PE lock.
2. To operate DS from OFF to Earth position key has to be
trapped in PE lock.
3. Key will be trapped in lock till DS is in Earth position.
Sequence of operation for BUS-A Earthing
1. To Earth power cable, key has to be trapped in PE lock.
2. Key suitable for PE lock shall be made available only with
authorized person. Authorized person will issue the key only
after ensuring that BUS-A is dead.
3. Trap the key in PE lock provided at riser panel and move DS of
riser to Earth postion.
4. Earth BUS-A by making DS and breaker of BUS coupler ON.
Sequence of operation for BUS-B Earthing
1. To Earth power cable, key has to be trapped in PE lock.
2. Key suitable for PE lock shall be made available only with
authorized person. Authorized person will issue the key only
after ensuring that BUS-B is dead.
Figure 6.4.4 - DS Facia
4. At a time, Disconnector switch can be operated either
electrically or mechanically but not simultaneously.
5. Closure of VCB is not possible unless the spring is fully
charged.
Figure 6.4.5 - Bus Coupler & Riser
BUS-A
BUS-B
Q1
DISCONNECTOR
SWITCH
1250A
Q1
DISCONNECTOR
SWITCH
1250A
Q0
VCB
1250A
PE
PE
KEY FROM
AUTHORIZED
PERSON
KEY FROM
AUTHORIZED
PERSON
EAR
TH
EAR
TH
OFF
OFF
ON
ON
Lock & Key Qty Details
PE: 1 Lock & 1 Key
CABLE
ACCESS
DS
OPERATION
