High Voltage Circuit BreakerHV AC Switchgear

relays and circuit breaker combination

closed circuit breaker has sufficient energy to open its contacts stored in one form
r another. When a protective relay signals to open the circuit, the store energy is
released causing the circuit breaker to open.
except in special cases where the protective relays are mounted on the breaker,
he connection between the relay and CB is by hard wiring.
Figure indicates schematically this association between relay and circuitbreaker. In
protection, the important parts of the circuit breaker are the trip coil, latching
mechanism, main contacts and auxiliary contacts.
he roles played by these components in the tripping process is clear from Figure
and the following step by step procedure takes place while isolating a fault:
The relay receives information, which it analyzes, and determines that the circuit
should be opened.
Relay closes its contacts energizing the trip coil of the circuit breaker.
The CB is unlatched and opens its main contacts under the control of the tripping
The trip coil is de energized by opening of the CB auxiliary contacts.
CBs are normally fitted with a number of auxiliary contacts, which are used in a
variety of ways in control and protection circuits.



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