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Unformatted text preview: rcuit is the secondary winding of C.T. connected to the relay operating coil.
(iii) The third circuit is the tripping circuit which consists of a source of supply, trip coil of
circuit breaker and the relay stationary contacts.
Under normal load conditions, the e.m.f. of the secondary winding of C.T. is small and the
current flowing in the relay operating coil is insufficient to close the relay contacts. This keeps the
trip coil of the circuit breaker unenergised. Consequently, the contacts of the circuit breaker remain
closed and it carries the normal load current. When a fault occurs, a large current flows through the
* The circuit to be protected carries a large current (normal or fault current) and is reduced to a suitable value
for relay operation with the help of a current transformer. Introduction to Switchgear 391 primary of C.T. This increases the secondary e.m.f. and hence the current through the relay operating
coil. The relay contacts are closed and the trip coil of the circuit breaker is energised to open the
contacts of the circuit breaker. 16.4 Bus-Bar Arrangeme...
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- Spring '12