ABB 615 series Technical Manual page 787

1MAC059074-MB A
615 series ANSI
Technical Manual
The function can also be used to avoid backup tripping of several breakers in case mistakes
occur during protection relay maintenance and tests.
50BF is initiated by operating different protection functions or digital logics inside the
protection relay. It is also possible to initiate the function externally through a binary
input.
50BF can be blocked by using an internally assigned signal or an external signal from a
binary input. This signal blocks the function of the breaker failure protection even when
the timers have started or the timers are reset.
The retrip timer is initiated after the pickup input is set to true. When the pre-defined time
setting is exceeded, 50BF issues the retrip and sends a trip command, for example, to the
circuit breaker's second trip coil. Both a retrip with current check and an unconditional
retrip are available. When a retrip with current check is chosen, the retrip is performed
only if there is a current flow through the circuit breaker.
The backup trip timer is also initiated at the same time as the retrip timer. If 50BF detects
a failure in tripping the fault within the set backup delay time, which is longer than the
retrip time, it sends a backup trip signal to the chosen backup breakers. The circuit
breakers are normally upstream breakers which feed fault current to a faulty feeder.
The backup trip always includes a current check criterion. This means that the criterion for
a breaker failure is that there is a current flow through the circuit breaker after the set
backup delay time.
A070696-ANSI V1 EN
Figure 393: Typical breaker failure protection scheme in distribution substations
Protection related functions
Section 5
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