Electrical Distribution Systems
CIRCUIT BREAKERS
When the latching mechanism is released, the circuit breaker will open, opening the "a" contact
for the tripping coil and de-energizing the tripping coil. Also, when the circuit breaker opens,
the "b" contact will close, thereby setting up the circuit breaker to be remotely closed using the
closing relay, when desired. The circuit breaker control switch may now be released.
Figure 8 Simple Circuit Breaker Control Circuit
- Breaker Closed
As you can see from Figure 7 or 8, the circuit breaker control circuit can be designed so that any
one of a number of protective features may be incorporated. The three most commonly-used
automatic trip features for a circuit breaker are overcurrent (as discussed previously),
underfrequency, and undervoltage. If any one of the conditions exists while the circuit breaker
is closed, it will close its associated contact and energize the tripping coil, which, in turn, will
trip the circuit breaker.
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