DESCRIPTION

BE1-50BF Breaker Failure Relays are three-phase, solid state relays designed to provide protection and

security for the power system against failure of the monitored breaker.

Breaker failure relaying is the use of a current monitoring relay to determine whether or not current

continues to flow into a faulted circuit some time after a circuit breaker has been instructed to interrupt the

circuit. In the event that current continues to flow into the faulted circuit (after a defined period of time has

elapsed sufficient for the breaker to have interrupted the current), then the circuit breaker is considered to

have failed, and steps must be initiated to trip the next set of breakers up stream in the power system. The

back up scheme must be designed to isolate both the faulted circuit and the failed breaker.

Following are several reasons why a breaker fails to clear a fault:

• Trip circuit can be open (broken wire, blown fuse, open trip coil).

• Interrupting mechanism can stick, leaving a single phase of a three-phase circuit connected.

• Interrupter can flash-over due to the loss of dielectric strength through contamination or damage.

• Operating mechanism can fail to operate.

Breaker failure relays detect these conditions and initiate contingency or back up procedures.

Typically, breaker failure protection is applied to transmission and sub transmission systems. However,

breaker failure protection may be applied to any portion of the power system where failure of a circuit

breaker to operate properly could result in severe system damage or instability.