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Circuit breaker failure protection

Take an example: say there is a permanent fault on overhead transmission line, the distance / line differential protection should operate and trip respect circuit breaker (CB) which is feeding the fault. This protection relay will initiate a 2 stage breaker failure (BF) relay too. If the CB has operated & cleared the fault BF will reset. If however CB has failed to open & fault on line is persisting then 1st stage will operate in 50ms time & give trip command to 2nd trip coil of failed CB and if CB still did not open then 2nd stage of BF relay in normally 150ms time will give trip command to all CBs of this substation (where CB has failed) as well as through PLC/ Pilot wire communication send trip command to remote end CB of faulty line to trip (if it has already not tripped).

SF6 (15KV to 250KV) and ACB are protectors, therefore failure protection system for these devices are to ensure that their switching position monitored after a fault. These state could be (Failure to trip or failure to clear).

There are Electromachnical, Solid State, Computer base devices which are setup before and after a circuit breaker for monitoring.

So you may have a computer base system which monitors circuit breaker efficiency and gives an alarm any failure occurs. Therefore Circuit breaker Protection system is simply a circuit breaker Fault Monitoring System which will trip a Designated CB where necessary.

There is a general perception that this BF protection is protection of CB which is wrong, it can max called backup support of CB.

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