Interlocking_Scheme___Transmission_dept.pdf

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Interlocking Scheme for Switchgears : -Electricity Transmission

Basic Conditions to be fulfilled :

1. One self resettable key switch for "Interlock Bypass" to be provided in each LCC panel to

bypass all interlocks in event of :

a. Any emergency when some interlocks are not working due to incomplete

operation of the gear.

b. Interlock signals from remote end are not working if the communication channel

fails

Each switch shall have a separate key and the switch shall be lockable in "Normal"

position only. When put in "Bypass" mode then it shall generate an alarm in SCS as well

as at NCC. Interlock Bypass key switch will not bypass SF6 Lock out condition.

2. For manual operations also, all the interlocks shall be checked, however to take care of

emergency cases such as loss of control supply or if the gear doesn't complete its full

operation then the "Interlock Bypass" feature shall be used to carry out the manual

operations.

3. Isolator shall be mechanically interlocked with its associated earthswitch.

4. The electrical operation to any equipment shall be blocked when the hand crank is

inserted for manual operation.

5. All feeders that feed to a remote substation shall have a VT irrespective of whether the

remote end is a transformer substation / Busbar.

6. The close/open status of all equipment shall be derived from minimum two aux. contacts.

For Eg : the status of CB shall be derived as follows : "Normally the CB is equipped with

two types of Contacts (52a-Normally open and 52b-Normally closed i.e the status of

contact is defined in CB open condition). Hence two 52a contacts shall be connected in

series for ‘close’ status and two 52b contacts in series for ‘open’ status. This philosophy

shall be used only for Interlocking purpose, and not for any status indications at SCS or

NCC".


7. For switching from Bay Control Unit / SCS, there shall be software interlocks which shall

be in series with the hardware interlocks. ‘Software Interlocks’ shall be a true replica of

the Hard ware interlocks and shall be incorporated in exclusive BCUs assigned for that

particular Bay.

8. For any non-standard configuration which are not a part of this document Prior approval

of interlocking scheme must be taken ( then review will be done at site.)

9. For Isolators, the end position status (for close as well as open) shall be taken for all

interlocks.

10. For withdrawable type CBs, operation in test position shall be allowed only in Local

mode from the switchgear. When CB is in Withdrawn condition CB will be free to

operate and will not be looking for any interlocks.

11. For Transformers operating in parallel, the Master/Follower logic shall be independent of

the status of associated CBs.

Changing of Master/Follower/Independent and Tap operations should be available at

SCS. Master/Follower modes shall be selectable for both Transformers. If ‘Master’ is off,

follower shall be automatically selected to ‘Independent auto’ mode.

As per our existing practice, raising tap means raising voltage and lowering tap means

lowering voltage (this philosophy is easy to understand). Hence, the tap numbering of

Transformer shall be arranged to suit for this practice (unlike phase-V).

12. The following points shall be checked in the case of SF6 pressure conditions:

SF6 pressure in the case of CB compartment shall have three stages:

a. Stage-1- Alarm

b. Stage-2- Trip (This stage shall be set well above the safe level. If the CB is failed

to trip and the pressure goes on decreasing, at Stage-3, the CB will be blocked for

any operation. SF6 trip will not initiate any CB fail protection).

c. Stage-3- Block operation (both Close and Open)

All other Compartments- Alarm at SCS and NCC and blocking of operation.

13. Wherever the interlocks demand to check the "No-Voltage" or "Voltage exists" condition

then all the 3 phases shall be monitored. In addition, for "No-Voltage" condition, it shall

be ensured that it represents a true "No-Voltage" condition by monitoring all associated

devices (such as VT isolator close, VT primary fuses health, VT secondary fuses healthy,

VT secondary MCB ON,……) .

14. The VT secondary shall have two MCBs as follows :

a. One at LCC panel to facilitate the isolation purpose during switching operations

and

b. One at the nearest point to the VT sec terminals (for eg : VT secondary box)

which shall monitor any fault in the control cable between this MCB to the MCB

in the LCC panel.

Both MCBs shall be monitored for VT secondary status.

The MCB monitoring the control cable shall be set at a higher value than the MCB in the

LCC panel.


15. In the case of feeders/Tx feeders, the remote status of switches shall be brought to the

local station (through redundant communication channels) and incorporated in the SCS

SLD for status monitoring. These statuses shall not be incorporated in the Interlocking

scheme at local station (unlike phase-V).

16. For systems having facility of selecting Local/Remote at SCS, it shall be possible to

select the Local/Remote for each bay separately.

17. For any Bay, all Earth switch operation shall be possible only from SCS, BCU or LCC

(Entire document shall be cross-checked for this point). Status of Earthswitches to be

extended to NCC. Though earthswitches shall not be operated from NCC, the facility

shall be extended to NCC and the links shall be kept open or software block at NCC to

prevent operation.

18. In ‘Maintenance’ mode, all protection trips should be blocked including SF6 second

stage. In this mode, only local operation from LCC shall be possible for all Bays and for

all switches. In case the SF6 pressure is less than the safe operating pressure (i.e < stage 3

or as per manufacturer's recommendation) then the CB should be blocked from operation.

19. The operation allowed in different modes shall be as follows :

a. Maintenance mode :

� L/R/M switch in Maintenance mode at LCC panel

b. Local mode from LCC :

� L/R/M switch in Local mode at LCC panel

c. Operation from Bay Control Unit (BCU)

� L/R/M switch in Remote mode at LCC panel

� BCU in Local

d. Operation from SCS in control room


� BCU in Remote

� TMMC/SCS in Local

e. Operation from Remote (NCC)


� BCU in Remote

� TMMC/SCS in Remote


&

&LCC : L/R/M Swich in Local

BCU : Local mode selection

LCC : Control Command

&

LCC : L/R/M Swich in Remote

BCU : Control Command

BCU : Remote mode selection


TMMC / SCS : Local mode

TMMC / SCS: Control command

&BCU : Remote mode selection


TMMC / SCS : Remote mode

NCC : Control command

LCC Local mode

BCU Local Mode

SCS Local Mode

NCC Mode

&LCC : L/R/M Swich in Maintenance

LCC : Control CommandMaintenance mode

The Interlock philosophy shall be explained in logic block diagram, in the following method:

Nature of operation LCC

mode

BCU

mode

SCS

mode

NCC

mode

Final

Output

Normal operation

Maintenance operation

On-load transfer operation

Note :

Apart from all conditions mentioned in this brochure, if the site requirements demands a

review/change in some of the points then O&M staff shall accordingly inform the concerned to

incorporate the changes.


224 226

22022M1 22M2

124 126

12012M1 12M2

132

134

130

13M1

13M2

232

234

230

23M1

23M2

1241 1261

22612241

364

36M1

464

46M1

264

26M1

164

16M1

BB R1

BB M1 BB M2

BB R2

SINGLE LINE DIAGRAM

FOR

BUS COUPLER & BUS SECTION &

BUS VT BAYS


A. BUS COUPLER / BUS SECTION / BUS VT BAYS :

1. CB Close interlock (120, 220, 130, 230,……..)

All conditions below shall be satisfied in Remote / SCS / BCU / LCC Local:

a. Corresponding both busbar isolators should be closed and sychro check

OR

Both Busbar isolators are open

b. Corresponding Maintenance earthswitches should be opened.

c. No relay anamoly (No other equipment operating)

d. SF6 pressure in CB > stage 2

e. CB Drive & Aux Supply healthy

f. Trip circuit supervision healthy

g. Lockout relay not operated

All conditions below shall be satisfied in LCC Maintenance mode :

a. Maintenance Earthswitches M1 and M2 Closed

b. No SF6 Lock out (SF6 at safe Operating pressure)

Example logic for #120 (Similar logic to be adopted for #220, #130 and #230)


2. CB Open interlock (120, 220, 130, 230,……..)

All conditions below shall be satisfied in Remote / SCS / BCU / LCC :

a. Open Command.

b. SF6 pressure < Stage 2

c. Protection Trip

d. No On-Load Transfer. (CB restrained from trip during Bus Transfer) (See Note 1)

All conditions below shall be satisfied in Maintenance mode :

a. Open Command

b. SF6 level healthy

Note 1 :

i. Bus Coupler (130) restrained from trip during

1. ON LOAD transfer of BB M1 – BB R1 or

2. Any ON LOAD transfer if Bus Section (1 & 2) are closed and Bus

Coupler 2 is open.

ii. Bus Coupler (230) restrained from trip during

1. ON LOAD transfer of BB M2 – BB R2 or

2. Any ON LOAD transfer if Bus Section (1 & 2) are closed and Bus

Coupler 1 is open.

iii. Bus Section (120 & 220) restrained from trip if

1. Bus Section 1 is closed and

2. Bus Section 2 is closed and

3. - Transfer from BB M1 – BB R1 with Bus Coupler 2 close and Bus

Coupler 1 open

OR

- Transfer from BB M2 – BB R2 with Bus Coupler 2 open and Bus

Coupler 1 close

o Bus Coupler OR Bus Section will be treated as Close only if both busbar

isolators and CB are closed.

o Bus Coupler OR Bus Section will be treated as Open if any one of the busbar

isolator or CB is Open.

Example logic for #120 (Similar logic to be adopted for #220, #130 and #230)


Logic for restraining Bus section CB / Bus Coupler CB from trip


3. Busbar Isolator Close / Open interlock (124, 126, 224, 226, 134, 132, 234, 232,……)


a. Corresponding busbar earthswitch Open

b. CB Open

c. Maintenance Earthswitches M1 and M2 Open

d. No relay anamoly (No other equipment operating)

e. No SF6 lockout (SF6 at safe operating pressure)


a. Corresponding Maintenance Earthswitch M1/M2 Closed

b. Corresponding Busbar Earthswitch Closed

c. No SF6 lockout (SF6 at safe operating pressure)

Example logic for #124 (Similar logic to be adopted for isolators of Bay #12, #22, #13, #23)


4. Busbar Earthswitch Close / Open interlock (1241, 1261, 2241, 2261….,)

All conditions below shall be satisfied in SCS / BCU / LCC Local / LCC maintenance:

a. All busbar isolators of corresponding bus to be Open

b. Busbar VT Isolator Closed

c. Busbar VT sec MCB ON

d. No Voltage condition.

e. No relay anamoly (No other equipment operating)

f. No SF6 lockout (SF6 at safe operating pressure)

Example logic for #1241 (Similar logic to be adopted for other Bus E/Sw)

5. Maintenance Earthswitch Close / Open interlock (12M1, 12M2, 22M1, 22M2, 13M1,

13M2, 23M1, 23M2….,)

All conditions below shall be satisfied in SCS / BCU / LCC Local / LCC Maintenance:

a. MBB isolator Open

b. RBB isolator Open


d. No SF6 lockout (SF6 at safe operating pressure)

Example logic for #12M1&#12M2 (Similar logic to be adopted for other M E/Sw)


6. Busbar VT Isolator Close / Open interlock (164, 264, 364, 464)

All conditions below shall be satisfied in Remote / SCS / BCU / LCC Local / LCC

Maintenance:

a. No Voltage condition on the Bus

b. Busbar VT MCB ON




a. Corresponding Maintenance Earthswitch M1 Closed (16M1, 26M1, …)

b. Corresponding Busbar Earthswitch Closed (1241, 1261, …..)


Example logic for #164 (Similar logic to be adopted for other Bus VT Isolators)

7. VT Maint Earthswitch Close / Open interlock (16M1, 26M1, 36M1, 46M1, ….,)


a. Busbar VT isolator Open

b. No Voltage condition on the Bus



Example logic for #16M1 (Similar logic to be adopted for other Bus VT M.Earthswitch)


SINGLE LINE DIAGRAM

FOR

FEEDER BAY

104

100

10M2

BB M1

BB R1

102

10M1

103

101

130

1064106M1

230

120

220

BB M2

BB R2

1241 1261

2241 2261


B. FEEDER BAYS :

1. CB Close interlock (100, 200, 300, 400,……..)


a. Any One Busbar (Main or Reserve) isolator alongwith Line isolator should be

closed and sychro check

OR

MBB, RBB & Line isolators are open

b. Corresponding Maintenance earthswitches should be opened. .







a. Maintenance Earthswitches M1 and M2 Closed

b. SF6 pressure healthy

Example logic for #100 (Similar logic to be adopted for other line bays)


2. CB Open interlock (100, 200, 300, 400,……..)


a. Open Command.


c. Protection Trip


a. Open Command


Example logic for #100 (Similar logic to be adopted for other line bays)


3. Main Busbar Isolator Close / Open interlock (104, 204, 304, …………)


a. - RBB Isolator, CB, Maint E/Sw M1 & M2 and corresponding BB E/Sw (1241 /

1261) Open

OR

- RBB Isolator and Bus Coupler 1 Closed

OR

- RBB Isolator, Bus Coupler 2, Bus Section (1 & 2) Closed

b. No relay anamoly (No other equipment operating)


Note :

During Bus transfer, the condition that CB and Line Isolator should be closed is

removed to ensure that the Bus transfer is still possible if for any reason the CB trips

when both busbar isolators are closed.


a. Maintenance Earthswitch M1 Closed



Example logic for #104 (Similar logic to be adopted for MBB isolators of other line bays)


4. Reserve Busbar Isolator Close / Open interlock (102, 202, 302, …………)


a. - MBB Isolator, CB, Maint E/Sw M1 & M2 and corresponding BB E/Sw (2241 /

2261) Open

OR

- MBB Isolator and Bus Coupler 1 Closed

OR

- MBB Isolator, Bus Coupler 2 and Bus Section (1 & 2) Closed



Note :

During Bus transfer, the condition that CB and Line Isolator should be closed is

removed to ensure that the Bus transfer is still possible if for any reason the CB trips

when both busbar isolators are closed.





Example logic for #102 (Similar logic to be adopted for RBB isolators of other line bays)

&

LCC Local mode

BCU Local mode

SCS Local mode

NCC mode

#102 Close / Open

#104 Open

#10M1 Open

&

LCC Maintenance mode

#10M2 Open

#100 Open

#10M1 Close

#2241 Close

No relay anamoly

SF6 level healthy

SF6 level healthy

#2241 Open

&

&#104 Close

#BC 1 Close

&

#104 Close

#BS 1 Close

#BS 2 Close

#BC 2 CloseNote : During Bus transfer, the condition that CB

and Line Isolator should be closed is removed to

ensure that the Bus transfer is still possible if for

any reason the CB trips when both busbar

isolators are closed


5. Line Isolator Close / Open interlock (103, 203, 303, …………)


a. Line E/Sw open

b. Maintenance E/Sw (M1 and M2) Open

c. CB Open


e. No SF6 lockout (SF6 at safe operating pressure)



b. Line Earth S/W closed


Example logic for #103 (Similar logic to be adopted for Line isolators of other bays)


6. Line Earth Switch Close / Open interlock (101, 201, 301, …………)


a. Line Isolator open

b. Line VT Isolator Closed

c. Line VT sec MCB closed

d. No Voltage condition.

e. No relay anamoly (No other equipment operating)

f. No SF6 lockout (SF6 at safe operating pressure)

Note :

For feeders which do not have a Line VT then the status of the remote end isolator

shall be checked. All new feeders shall have Line VT

Example logic for #101 (Similar logic to be adopted for Line E/Sw of other bays)

7. Maintenance Earth Switch Close / Open interlock (10M1, 10M2, 20M1, …)


a. MBB & RBB Isolator open

b. Line Isolator open



Example logic for #10M1&#10M2 (Similar logic to be adopted for M E/Sw of other bays)


8. Line VT Isolator Close / Open interlock (1064, 2064, 3064, 4064, ……..)


Maintenance:

a. No Voltage condition on the Line

b. Line VT MCB ON





b. Corresponding Line Earthswitch Closed (101, 201, …..)


Example logic for #1064 (Similar logic to be adopted for VT isolators of other line bays)

9. Line VT Maintenance Earthswitch Close / Open interlock (106M1, 206M1, 306M1,

406M1, ….,)


a. Line VT isolator Open

b. No Voltage condition on the Line.



Example logic for #106M1 (Similar logic to be adopted for VT M.ESw of other line bays)


SINGLE LINE DIAGRAM

FOR

TRANSFORMER BAY

114

110

111

BB M1

BB R1

112

11M1

130 230

120

220

BB M2

BB R2

1241 1261

22612241

BB M1

BB R1

130 230

120

220

BB M2

BB R2

1241 1261

22612241

184 182

180

18M1

181


C. TRANSFORMER BAYS (HV side ):

1. CB Close interlock (110, 210, ……..)


a. Any One Busbar (Main or Reserve) isolator should be closed and LV side CB

(180, 280, …) Open.

OR

MBB, RBB isolators at HV & LV side are open

(Note : LV side interlocks to be taken only if it is in the same substation.)

b. Maintenance earthswitch M1 and Line earthswitch (111, 211,…) should be open .







a. Maintenance Earthswitches M1 Closed

b. Transformer E/S (111, 211, …) closed.


Example logic for #110 (Similar logic to be adopted for other Transformer HV bays)

& &

No relay anamoly

Trip Circuit supervision healthy

Aux Supply healthy

SF6 level > Stage 2

&

LCC Local mode

BCU Local mode

SCS Local mode

NCC mode


#111 Closed

#11M1 Closed

SF6 level healthy

#110 Close

Lockout relay not operated

#114 Closed

#112 Closed

CB Drive healthy

#11M1 Open

#111 Open

#112 Open

#114 Open

Note : For additional safety and To

differentiate between “Operation

mode” and “Maintenance mode”

&

#182 Open

#184 Open

#180 OpenNote : This condition shall be fulfilled

only if LV side switchgear is in the

same substation.


2. CB Open interlock (110, 210, ……..)


a. Open Command.


c. Protection Trip


a. Open Command


Example logic for #110 (Similar logic to be adopted for Transformer HV bays)


3. Main Busbar Isolator Close / Open interlock (114, 214, ………)


a. – RBB Isolator, CB, Maint E/Sw M1 ,Corresponding BB E/Sw (1241 / 1261) and

Transformer E/Sw Open. (If LV side switchgear is in the same substation, then it

shall also check that LV side Transformer Earth/Sw and LV side Maint E/Sw are

Open).

OR


OR

- RBB Isolator, Bus Coupler 2 and Bus Section (1 & 2) Closed



Note :

During Bus transfer, the condition that CB should be closed is removed to ensure that

the Bus transfer is still possible if for any reason the CB trips when both busbar

isolators are closed.





Example logic for #114 (Similar logic to be adopted for MBB isolators of Tx HV bays)


4. Reserve Busbar Isolator Close / Open interlock (112, 212, …………)


a. – MBB Isolator, CB, Maint E/Sw M1, Corresponding BB E/Sw (2241 / 2261),

Transformer E/Sw Open. (If LV side switchgear is in the same substation, then it

shall also check that LV side Transformer Earth/Sw and LV side Maint E/Sw are

Open)

OR


OR

- MBB Isolator, Bus Coupler 2 and Bus Section (1 & 2) Closed



Note :








Example logic for #112 (Similar logic to be adopted for RBB isolators of Tx HV bays)


5. Transformer Earth Switch Close / Open interlock (111, 211, …………)


a. MBB and RBB Isolator open

b. If VT is available on HV side then VT Isolator and VT MCB shall be ON along

with "No Volt" condition

c. LV side MBB and RBB Isolator shall be Open (This condition to be fulfilled only

if the LV side switchgear is in the same substation).


e. If the Tx LV side is connected to 11kV Swgr of withdrawable CB, then the CB

shall be in Test Position OR Racked out position. For non withdrawable CBs Bus

bar isolator shall be open.

f. If the Tx LV side has a ETx then the LVAC CB shall be in test/rackout position

OR ETx FSU shall be OFF.

g. No relay anamoly (No other equipment operating)

h. No SF6 lockout (SF6 at safe operating pressure)

Example logic for #111 (Similar logic to be adopted for Line E/Sw of Tx HV bays)

&

LCC Local mode

BCU Local mode

SCS Local mode


#11M1 / #111

Close / Open

#114 Open

No relay anamoly

SF6 level healthy

#112 Open

Line VT Isolator #1164 Close

“No-Voltage” condition

Line VT sec MCB ON

#184 Open

#182 Open

Note : This condition shall be fulfilled

only if VT is exists on the HV side of

Transformer.

Note : This condition shall be

fulfilled only if LV side switchgear

is in the same substation &

# 180 in Test position

#180 in Rackout position

LVAC Inc-1 CB in Test

LVAC Inc-1 CB in Rackout

Earthing Tx FSU is OFF

Note : This condition shall be fulfilled

only if LV side has a Earthing

Transformer

Note : This condition shall be

fulfilled if LV side switchgear

is of withdrawable CB

6. Maintenance Earth Switch Close / Open interlock (11M1, 21M1,…)

a. Same interlocks as Transformer E/Switch (111, 211, ….)


7. Line VT Isolator Close / Open interlock (1164, 2164, ……..)


Maintenance:


b. Line VT MCB ON







Example logic for #1164 (Similar logic to be adopted for VT isolators of Tx HV bays)

8. Line VT Maint Earthswitch Close / Open interlock (116M1, 216M1, ….)



b. No Voltage condition on the Line



Example logic for #116M1 (Similar logic to be adopted for VT M.ESw of Tx HV bays)


D. TRANSFORMER BAYS (LV side ):

1. CB Close interlock (180, 280, ……..)


a. Any One Busbar (Main or Reserve) isolator should be closed, HV side CB (110,

210, …) Close and Synchro Check.

OR

MBB, RBB isolators at LV & HV side are open

(Note : HV side interlocks to be taken only if it is in the same substation.).

b. Maintenance earthswitch M1 and line earthswitch (181, 281,…) should be open.

c. Voltage exists in all 3 phases. (This condition is used only to close CB. If the VT

MCB is switched off when CB is ON, loss of voltage should not trip the CB)


e. SF6 pressure in CB > stage 2

f. CB Drive & Aux Supply healthy

g. Trip circuit supervision healthy

h. Lockout relay not operated.


a. Maintenance Earthswitches M1 Closed

b. Line E/S (181, 281, …) closed.


Example logic for #180 (Similar logic to be adopted for other Transformer LV bays)


2. CB Open interlock (180, 280, ……..)


a. Open Command.


c. Protection Trip


a. Open Command


Example logic for #180 (Similar logic to be adopted for Transformer LV bays)


3. Main Busbar Isolator Close / Open interlock (184, 284, ………)


a. – RBB Isolator, CB, Maint E/Sw M1 ,Corresponding BB E/Sw (1241 / 1261) and

Transformer E/Sw Open . (If HV side switchgear is in the same substation, then it

shall also check that HV side Transformer Earth/Sw and HV side Maint E/Sw are

Open)

OR


OR

- RBB Isolator, Bus Coupler 2 and Bus Section (1 & 2) Closed



Note :








Example logic for #114 (Similar logic to be adopted for MBB isolators of Tx LV bays)


4. Reserve Busbar Isolator Close / Open interlock (182, 282, …………)


a. – MBB Isolator, CB, Maint E/Sw M1, Corresponding BB E/Sw (2241 / 2261) and

Transformer E/Sw Open . (If HV side switchgear is in the same substation, then it

shall also check that HV side Transformer Earth/Sw and HV side Maint E/Sw are

Open)

OR


OR

- MBB Isolator, Bus Coupler CB 2 and Bus Section (1 & 2) Closed



Note :








Example logic for #182 (Similar logic to be adopted for RBB isolators of Tx LV bays)


5. Transformer Earth Switch Close / Open interlock (181, 281, …………)


a. MBB and RBB Isolator open

b. VT Isolator and VT MCB shall be ON along with "No Volt" condition

c. HV side MBB and RBB Isolator shall be Open (This condition to be fulfilled only

if the HV side switchgear is in the same substation).


e. If the Tx LV side is connected to 11kV Swgr of withdrawable CB, then the CB

shall be in Test Position OR Racked out position. For non withdrawable CBs Bus

Bar isolator shall be open.

f. If the Tx LV side has a ETx then the LVAC CB in test/rackout position OR ETx

FSU shall be OFF.

g. No relay anamoly (No other equipment operating)

h. No SF6 lockout (SF6 at safe operating pressure)

Note : (For station having Transformer directly fed from other station)

- If the Tx HV side is equipped with an Earth switch (111, 211, …) then it shall have

the same logic as E/Sw (181, 281, ……..)

Example logic for #181 (Similar logic to be adopted for Line E/Sw of Tx LV bays)

6. Maintenance Earth Switch Close / Open interlock (18M1, 28M1,…)

a. Same interlocks as Line E/Switch (181, 281, ….)


7. Line VT Isolator Close / Open interlock (1864, 2864, ……..)


Maintenance:


b. Line VT MCB ON







Example logic for #1864 (Similar logic to be adopted for VT Isolator of Tx LV bays)

8. Line VT Maint Earthswitch Close / Open interlock (116M1, 216M1, ….)



b. No Voltage condition on the Line.



Example logic for #186M1 (Similar logic to be adopted for VT M.ESw of Tx LV bays)


E. METAL ENCLOSED AC SWITHCGEAR (with removable CB) –

SINGLE BUSBAR :

IEC 62271-200 in addition to IEC 60694 to be followed

Interlocks between different components of the equipment are provided for reasons of protection

and for convenience of operation. The following provisions are mandatory for main circuits.

Basic conditions :

� The withdrawal or engagement of a CB shall be prevented unless it is in the open position

� The operation of a CB shall be prevented unless it is only in the service, disconnected,

removed, test or earthing position.

� The interlock shall prevent the closing of the CB in the service position unless any

auxiliary circuits associated with the automatic opening of these devices are connected.

� The interlock shall prevent the disconnection of the auxiliary circuits with the circuit-

breaker closed in the service position.

� Rack-in of CB to service position from test/rackout position shall not be possible unless

the associated Line earthswitch and Busbar earthswitch are open.

� Closing of Line Earthswitch shall be possible only if the CB is in test position or rackout

position.

� Closing of Busbar Earthswitch shall be possible only if all the associated CBs are in test

position or rackout position.

� CB cubicle door shall not open if the CB is in service and closed.

� Manual ON/OFF switches shall be provided in service as well as test position.

� It should be possible to lock the Busbar shutter and Feeder Shutter in Close as well as

Open position. It should be possible to keep the feeder shutter opened and locked when

the bus bar shutters are closed and locked.

� Busbar shutters shall be coloured, "Signal Red' Colour 537 of BS 381C and shall be

clearly labeled 'BUSBARS' in large white letters. Feeder circuit shutters shall be

coloured 'Lemon' Colour 355 of BS 381C and shall not be labeled.

� On Bus-Section equipment both sets of shutters shall be coloured, "Signal Red' Colour

537 of BS 381C and shall be clearly labeled 'BUSBARS' in large white letters. In

addition each shutter shall carry a white arrow pointing to the section of busbar with

which the shutter is associated.

� To facilitate pressure test of the cable, it should be possible to isolate VT irrespective of

the line earthswitch status when the circuit is dead.

� Viewing window for physical verification of earthswitch required.

� LV Cubicles should be hinged and shall be easily opened by lockable latching handles.

LV Cubicles should not be closed with nut and bolts. Access to LV VT MCB shall be

available without opening the LV compartment.


1. Incomer CB Close interlock (A180, A280, ……..)

All conditions below shall be satisfied in Remote / SCS / BCU / Local :

a. CB in service position.

b. Transformer Earthswitch (A181, A281,…..) Open

c. Busbar Earthswitch (A1241, A1261,…..) Open

d. HV side CB (110, 210, ….) should be close (This condition to be fulfilled only if

the HV side CB is in the same substation)

e. Voltage exists in all 3 phases. (This condition is used only to close CB. If the VT


f. Synchro check

g. CB Drive & Aux Supply healthy

h. Trip circuit supervision healthy

i. Lockout relay not operated

In test position, CB shall free of all interlocks.

Example logic for A180 (Similar logic to be adopted for other incomers)

&

Trip Circuit supervision healthy

Aux Supply healthy

LCC Local mode

BCU Local mode

SCS Local mode

NCC mode

A180 in Test Position

A180 Close

Lockout relay not operated

CB Drive healthy

A1241 Open

A181 Open

#110 CloseNote : This condition shall be fulfilled

only if HV side switchgear is in the

same substation.

Voltage exist in all 3 ph

Note : This condition is used only to close CB.

If the VT MCB is switched off when CB is ON,

loss of voltage should not trip the CB”

A180 in Service Position

Synchro Check


2. Outgoing CB Close interlock (A120, ……..)



b. Transformer Earthswitch (A181, A281,…..) Open


d. HV side CB (110, 210, ….) should be close (This condition to be fulfilled only if

the HV side CB is in the same substation)

e. Voltage exists in all 3 phases. (This condition is used only to close CB. If the VT


f. Synchro check

g. CB Drive & Aux Supply healthy

h. Trip circuit supervision healthy

i. Lockout relay not operated


Example logic for A120 (Similar logic to be adopted for other Bus Section CB)


3. Outgoing CB Close interlock (A100, A200, ……..)



b. Line Earthswitch (A101, A201,…..) Open


d. CB Drive & Aux Supply healthy

e. Trip circuit supervision healthy

f. Lockout relay not operated


Example logic for A100 (Similar logic to be adopted for other outgoing feeders)

4. Incomer / Bus Section / Outgoing CB Open interlock (A180, A280, A120, A100……..)

All conditions below shall be satisfied:

a. - Protection Trip OR

- Emergency Trip (if equipped) OR

- Open command from Bay (Local / BCU / SCS / NCC as per appropriate

selection)


5. Transformer Earthswitch (Incomer) Close/Open interlock (A181, A281,……..)

All conditions below shall be satisfied in SCS / BCU / Local :

a. CB in test position OR fully rackout position

b. HV side MBB and RBB Isolator shall be Open (This condition to be fulfilled only

if the HV side switchgear is in the same substation).

c. VT in service

d. VT fuses healthy

e. VT MCB ON

f. No Voltage condition

g. Corresponding LVAC CB in test/rackout position OR ETx FSU shall be OFF

Example logic for A181 (Similar logic to be adopted for other Inc E.Sw)

6. Busbar Earthswitch Close/Open interlock (A1241, A1261……..)



b. VT in service

c. VT fuses healthy

d. VT MCB ON

e. No Voltage condition

Example logic for A1241 (Similar logic to be adopted for other Bus E.Sw)


7. Line Earthswitch (Outgoing) Close/Open interlock (A101, A201……..)



b. VT in service

c. VT fuses healthy

d. VT MCB ON

e. No Voltage condition

Example logic for A101 (Similar logic to be adopted for other Line E.Sw)

8. VT Isolation / In service (A186, A286, A106, A206,A16, A26 ……..)

All conditions below shall be satisfied:

a. VT MCB ON

b. VT fuses healthy

c. No Voltage condition


F. METAL ENCLOSED AC SWITHCGEAR (provided with disconnectors)

– SINGLE BUSBAR :

IEC 62271-200 in addition to IEC 60694 to be followed

Interlocks between different components of the equipment are provided for reasons of protection

and for convenience of operation. The following provisions are mandatory for main circuits.

� Interlocks shall be provided to prevent operation of disconnectors under conditions other

than those for which they are intended (refer to IEC 62271-102).

� The operation of a disconnector shall be prevented unless the circuit-breaker, switch or

contactor is in the open position. o NOTE 1 This rule may be disregarded if it is possible to have a busbar transfer in a double busbar

system without current interruption.

� The operation of the circuit-breaker, switch or contactor shall be prevented unless the

associated disconnector is in the closed, open or earthing position (if provided).

� Earthing switches should be interlocked with the associated disconnectors.

� Apparatus installed in main circuits, the incorrect operation of which can cause damage or

which are used for securing isolating distances during maintenance work, shall be

provided with locking facilities (for example, provision for padlocks).

� If earthing of a circuit is provided by the main switching device (circuit-breaker, switch

or contactor) in series with an earthing switch, the earthing switch shall be interlocked

with the main switching device. In such cases the CB shall look for the "No-Voltage"

condition.

� Provision shall be made for the main switching device to be secured against unintentional

opening, for example, by disconnection of tripping circuits and blocking of the

mechanical trip. o NOTE 2 Instead of an earthing switch, also a disconnector in the earthing position is possible.

� If non-mechanical interlocks are provided, the design shall be such that no improper

situations can occur in case of lack of auxiliary supply. However, for emergency control,

the manufacturer may provide additional means for manual operation without

interlocking facilities. In such case, the manufacturer shall clearly identify this facility

and define the procedures for operation.

� If an interlock exists, then the corresponding control gate to insert manual operation

handle should not open.

� If Earthing is achieved by closing the Circuit Breaker, electrical closing should be

enabled.


G. LVAC :

a. Each section in the LVAC board shall be fed via their respective Incomers. Bus-

Section shall remain normally open.

b. Auto change over scheme shall be incorporated to close the respective Bus-Section

CB if voltage on any section fails and vice versa.

c. Auto changeover scheme shall work only if the Incomer CBs and Bus Section CB are

in service position

d. In addition to Auto changeover scheme there shall be a Manual mode for supply

change over

e. Momentary Paralleling of Incomers during changeover is allowed in Auto as well as

Manual mode to ensure that there is no supply interruption during change over

f. In Test/Rackout position the Incomer CBs and Bus Section CB shall be free of all

interlocks.

Interlocking_Scheme___Transmission_dept.pdf

Documents

status of cb

software interlocks

close status

hardware interlocks

end position status

status of contact

status indications

closeopen status