IEEE C37.119-2005 IEEE Guide for Breaker Failure Protection of Power Circuit Breakers.
While infrequent, circuit breakers occasionally fail to trip, or fail to clear a fault. Depending on the power system network topology other circuit breakers must then be called upon to trip and isolate the sources con- tributing to the fault. Referring to Figure 1, assume a fault exists between breaker 3 and breaker 4. Protective relays associated with breaker 3 and breaker 4, designed to detect faults on the line between these breakers, operate and command breaker 3 and breaker 4 to trip. In this example, breaker 3 fails to interrupt the fault current. Therefore, all sources that continue to supply fault current through breaker 3 must be interrupted. Assuming sources at stations A and C, locally, breakers 2, 5, and 7 must be opened, or remotely, breakers 1, 6, and 8 must be opened. To implement remote breaker failure backup protection for breaker 3, the protective relays at breakers 1, 6, and 8 must have overreaching elements that sense faults anywhere on the line between breaker 3 and breaker 4, and operate after a time delay, typically about 0.5 seconds. This time delay is required to allow time for the local line protection on breaker 3 to operate, and for the breaker to successfully clear the fault, recogniz- ing that the local protective relay scheme on breaker 3 may include time delayed tripping to coordinate with other protective relays. Remote backup protection does not have the benefit of knowing exactly when the breaker is commanded to open. Therefore, the remote backup protection must include sufficient time delay to accommodate all possible tripping delays. Local breaker failure protection, on the other hand, receives a signal directly from the line protection relays at the same station as the impaired breaker, indicating when the trip command is sent to the breaker. The local breaker failure protection only needs to wait for the breaker to successfully clear the fault. IEEE C37.119 pdf download.