Page 346 - Practical Power System and Protective Relays Commissioning

Protective Relays Testing and Commissioning Chapter | 20 341

5. Load Tests
5.1 Current Transformer and Polarity Tests

This test is done by load current when its value is above 25% 50% of
the I nominal of the relay.
Remove the tripping links at both sides of the relay.
Measure the current input to the relay for each phase and in the neutral
wire of the CT at both ends of the line, as shown in Fig. 20.4.3.
The reading in each phase should be near 1 A for CT secondary rated
1 A and near 0 in a neutral connection of the CT.
5.2 Stability Load Test
1. SC (Make a short circuit) between the two phase Y and B at both ends of
the line to simulate on external fault in phase R of the relay with a load
current of 25% 50% I N check that the relay will remain stable.
2. Check the operation of the relay when short-phase R with neutral at one
end or reverse the pilot wires at one end of the line to make the protec-
tion unbalanced.
6. Pilot Wire Tests
1. Make SC on a pilot cable. Check the operation of the pilot wire supervi-
sion relay and its alarm.
2. Open the pilot wires and check the operation of the supervision relay and
its alarm.
3. Reverse the pilot wires at one end only and check the supervision relay
will not operate.

FIGURE 20.4.3 Load test measurements.