Page 380 - Offshore Electrical Engineering Manual

Protection Relays 367

test plug are shorted out by links, so as to prevent high voltages appearing across the
CT secondary when the test plug is inserted.
Overcurrent induction disc relays used offshore usually have a current/time oper-
ating characteristic in accordance with BS EN 60255-151 for an inverse definite
minimum time relay. There are, however, relays with other inverse time characteris-
tics in use, and so it is important that the manufacturer’s commissioning and operat-
ing documentation is immediately available during any testing. The arrangements for
performing tests on the various elements are as follows. Figs 7.4.6 and 7.4.7 show
how the test circuit is connected:

1. With the TM at 1.0% and 100% of CT secondary current apply two times cur-
rent setting. The operating time should be checked and compared with the relay
characteristic.

o/c E/F o/c
phase phase
R B

2 4 6 8 10

1 3 5 7 9

+ –
Additional Trip
contacts circuit

R

Y

B

FIGURE 7.4.6
A typical triple-pole overcurrent and residually connected earth fault relay. E/F, earth fault;
o/c, overcurrent.