Page 289 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 283

I F 5 13,856 A
I S 5 800 A

13; 856
PSM 5 5 17:32
800
Using a standard inverse curve of the relay then we have the relay
operating time T R :
0:14 0:14
T R 5 0:0221 5 0:0221
PSM 17:32
T R 5 2.385
Assuming that the relay should operates on 1 second then we have:
t.operation 5 TM.T R
Where TM 5 time multiplier
1
TM 5 5 0:419
2:385
Relay (A) setting:
I set 5 800 A (Primary)
I set secondary 5 0.5 A
PSM 5 17
TM 5 0.4
Operating time for a fault at end B will be:

0:14
t:operation 5 0:4 3 0:0221
17
t.operation 5 0.96 seconds

19.1.3 TRANSFORMER OVERCURRENT PROTECTION

Transformer overcurrent protection is illustrated in Fig. 19.1.2.
Transformer data:
250 MVA 220/66 kV Z Tr % 5 10% on MVAb 5 100
Relay R 2 setting on low voltage (LV) feeder F 1:

FIGURE 19.1.2 Transformer overcurrent protection.