Page 333 - Practical Power System and Protective Relays Commissioning

328 Practical Power System and Protective Relays Commissioning

trip circuit E F and G H. Then we connect relay trip contact to the timer
stop points of the tester as dry or No-Voltage contact.

1. Relay data:
11 kV OC relay I set 5 1.2 I n
CT ratio 5 1000/1 relay characteristic used is SI
TD 5 1 I sc or I inst 5 6 I n
I pickup 5 I set 6 5%
I drop out . I set 5% I set
where I n 5 relay nominal current 5 1A
2. Pickup/drop off test:
1. Inject a current in the secondary circuit of the relay and increase the
current gradually from 0 up to 1.2 A. Then, when the relay led illumi-
nates, put this value as the pickup value, say 1.26 A, then decrease
the value of the injected current until the relay led switches off then
record it as a drop value, say 1.14 A.
2. Check that the value of I pickup within the value of I set 6 5%
I pickup 5 1.26-1.2 1 0.05 3 1.2 5 1.26. Then it is correct.
3. Check the drop out value $ I set 5% I set
I drop out 5 1.14 A-1.2 0.05 3 1.2 5 1.4. Then it is correct.
Check this for each phase of the relay. This means phases (Y) and
(B). If we have a modern test set we can inject three phases at the same
time and check the pickup and drop out values from the instantaneous
contact of the relay. As shown in Fig 20.2.2 the test for pH pH values is
repeated.

3. Checking of the relay characteristic:
1. Inject the current at two times the I set , three times the I set , and four
times the I set .
2. Check the trip time at each value.
3. From the relay characteristic curve check the value of times at
PM 5 1.0
for 2 3 I set ,3 3 I set ,4 3 I set .
4. Check that the difference between measured times and curve times is
within 6 5%, repeat the test for pH pH injection.
5. Instantaneous element test:
For this test inject the current and switch off very fast as this
current setting is high (6 I n ) and can damage the relay circuit.
Then inject 6 A and check the operating time in milliseconds.
6. Fill in the test results as shown in the test sheet in Table 20.2.1.