Page 332 - Practical Power System and Protective Relays Commissioning

Protective Relays Testing and Commissioning Chapter | 20 327

Subchapter 20.2

Overcurrent Relay Testing and
Commissioning

20.2.1 SECONDARY INJECTION TESTS
20.2.1.1 Nondirectional Overcurrent Relays Testing

Test Connection
As shown in Fig. 20.2.1 to test an OC relay in service we need to isolate
the links A B and C D and to short the CT secondary circuit by closing
the link A C.
As we know, during CT loading if there is an open circuit this will gener-
ate a dangerously high voltage (HV) on the secondary of the CT—dangerous
to personnel and capable of damage to the CT insulation (sometimes exceed-
ing 15 20 kV)—this exists in an AC relay circuit.
The injecting leads of the relay test set are then connected to the relay
side. This means B&D points to R&N points on the test set, respectively, for
the AC circuit of the relay and for the DC circuit of the relay we isolate the
relay contact “trip contact" by opening the two isolating links in the relay

FIGURE 20.2.1 Single-phase pickup/drop out test for OC relay connections.