Circuit Breaker Fail Protection; Circuit Breaker Fail Implementation - GE P50 Agile P253 Technical Manual

6 Protection Functions
to the relay, for example, when CB (52A) contact of CB is high. This function is deactivated when the
motor is shutdown and also during the inhibit time delay T inhib.
2.11

Circuit Breaker Fail Protection

When a fault occurs one or more protection devices will operate and issue a trip command to the
relevant circuit breakers. Operation of the circuit breaker is essential to isolate the fault and prevent, or
limit, damage to the power system. For transmission and sub-transmission systems slow fault
clearance can also threaten system stability.
For these reasons, it is common practise to install Circuit Breaker Failure protection (CBF). CBF
protection monitors the circuit breaker and establishes whether it has opened within a reasonable
time. If the fault current has not been interrupted following a set time delay from circuit breaker trip
initiation the CBF protection will operate. This means the upstream circuit breakers are back-tripped to
ensure that the fault is isolated.
CBF operation can also reset all start output contacts ensuring that any blocks asserted on upstream
protection are removed.
2.11.1

Circuit Breaker Fail Implementation

Circuit Breaker Failure Protection is implemented in the CB FAIL column of the relevant settings
group.
The circuit breaker failure protection incorporates CB Fail Timer. For any protection trip the CB Fail
Timer is started and normally reset when the circuit breaker opens to isolate the fault. If breaker
opening is not detected the CB Fail Timer times out and close an output contact assigned to breaker
fail (using the I/O assignment feature). This contact is used to back-trip upstream switchgear,
generally tripping all infeeds connected to the same busbar section.
6-24
P50 Agile P253
P253/EN M/C