Circuit breakers are switches used in power systems operating at high voltages and currents to protect circuits from faults. They can manually or automatically disconnect circuits under normal and abnormal load conditions. When a protective relay detects a fault, it sends a tripping signal to the circuit breaker, which then isolates the faulty part of the power system by opening its moving contacts from the fixed contacts.

1. By Jennifer Kumein.VP

2.  The power system operating at very high
voltages and currents require a more
controllable switch called as Circuit
Breakers(CB).
 At homes we use switches and fuses for small
appliances. Similarly in industries to protect
high capacity circuits we use CB which does
the same ON/OFF operation, but protects
the system from different faults.

3.  A Circuit Breaker can make or break a circuit
either manually or automatically under all
conditions viz, no load, full load and short
circuit conditions.
 Make/break circuit either manually or
automatically under
Normal
Condition
Fault
Condition

4.  A protective relay detects the abnormal
conditions and sends a tripping signal to the
CB. After receiving the trip command from
the relay, the CB isolates the faulty part of
the power system.
 Main parts of CB
Fixed contact
Moving contact

5.  Under normal conditions : Contacts are
closed and will not open automatically until
and unless the system becomes faulty or by
remote whenever desired.
 Under fault conidtions : Trip coils of the
breaker get energized and the moving
contacts are pulled apart by some
mechanism, thus opening the circuit.