Page 365 - Practical Power System and Protective Relays Commissioning

360 Practical Power System and Protective Relays Commissioning

However, when impedance passes from zone A to zone B only or from
zone C to zone B only, this is considered as an external faults and no trip
will occur.

20.8.2 RELAY CONNECTION

Refer to the following (Fig. 20.8.2), for out-of-step relay test connections

FIGURE 20.8.2 Out-of-step relay test connections.

20.8.3 TEST PROCEDURE
By injecting a fixed current of 1 or 2 A then the value of the injected voltage
is changed to simulate the following conditions and the relay response is
checked as follows:
Impedance passes from Z A -Z B -Z C -trip;
Impedance passes from Z C -Z B -Z A -trip;
Impedance passes from Z A -Z B -no trip;
Impedance passes from Z C -Z B -no trip.