Transformer Short circuit current calculation

Pole-Discrepancy Protection Scheme

Pole-Discrepancy Protection

PD scheme shall be provided for three single-pole operating type CBs

The pole-discrepancy protection shall use auxiliary contacts in the different phases, so that

a trip function shall be achieved for discrepancy for both closing and opening operations of

the breaker. The pole-discrepancy protection for CB shall be two-stage type. Both stage

Tripping relays shall be self-reset type with hand-reset targets.

Two-Step Pole-Discrepancy Protection

Upon occurrence of pole-discrepancy, the time-delayed functions shall be provided in twosteps.

i. The first-step shall trip the breaker with discrepancy. The time delay shall be sufficient

enough to avoid mal-functions due to the differences in operating times of differentpoles

and shall have additional adequate safety margin.

ii. The second-step shall be time delayed so that if the attempt to trip the CB from firststep

in discordance protection is successful, the function from second-step is inhibited.

If first-step is unsuccessful, all adjacent CB's to the faulty breaker in the station shall be

tripped (not required for double bus scheme to avoid major disturbance related with

tripping large number of CBs). Remote CB tripping (if required) shall also be initiated.

iii. In addition to above, each step shall have adequate contacts for annunciation, SOE and

SCADA functions shall be provided and wired accordingly.

iv.Pole-Discrepancy transfer trip receive relays 85PD-1 & 85PD-2 shall operate 94-1 & 94-2 of line protection tripping relays (similar to BFP scheme).For 380KV & 230KV system, Pole-Discrepancy receive relays 85PD-1 and 85PD-2 (PD only for three single pole CBs only) shall be high security self-reset relays and mounted

in Set-1 & 2 protection panels to operate 94-1 & 2 respectively of line (as applicable).

For system, Pole-Discrepancy receive relays 85PD shall be high security self-reset

relays and mounted in Set-1 protection panels to operate 94-1 & 94-2 of each (as

Applicable) ( PD transfer-trip scheme shall be via totally independent channel).

PD stage-1

PD stage-2

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Check CB Anti Pumping Function / Trip Free Function

Check CB Anti Pumping Function / Trip Free Function {at local and

remote position) and (at test and service position)}

Step 1: Ensure Gas, Air and DC Supply is normal for the CB under test.

Step 2: Close the Breaker Electrically and Hold the Control Switch in

‘CLOSE’ position.

Step 3: Trip the Breaker by externally extending the DC Supply to Trip

Circuit. (Not by any trip relays which is used for close interlock)

Step 4: Observe the Breaker to ‘TRIP’ and remain in ‘OPEN’ position &

Does not close.

Step 5: Thus Anti Pumping function found working with the above

Sequence.

Protection-communication channels for lines

Protection-communication channels for lines:

Following number of independent channels shall be provided for protection of line (set-1 & set-

2 groups of channels shall be on separate communication routes):

 Lines at Both Ends per Line

a. Set-1 channels (on route-1):

• Channel(s) for set-1 Differential protection (87L-1)-No of channel will be increase depend on input current source of scheme

• Channel for set-1 Distance protection (21-1) send / receive

• Channel for set-1 DEF (67N-1) send / receive.

• Channel for BFP Direct Transfer Trip-1 send / receive.

• Channel for Pole-Discrepancy Transfer trip-1 send / receive.

b. Set-2 channels (on route-2):

• Channel(s) for set-1 Differential protection (87L-2)-No of channel will be increase depend on input current source of scheme

• Channel for set-2 Distance protection (21-2) send / receive.

• Channel for set-2 DEF (67N-2) send / receive.

• Channel for BFP Direct Transfer Trip-2 send / receive.

• Channel for Pole-Discrepancy Transfer trip-2 send / receive.