Functions
6-125
7SJ63 Manual
C53000-G1140-C120-1
breaker successfully cleared the fault current, therefore, the device can be pro-
grammed such that only the current flow criterion is used to determine breaker status.
The current criterion is met if at least one of the three phase currents exceeds the cur-
rent flow monitoring setting entered at address
(see Subsection 6.1.1). Evalua-
tion of the circuit breaker auxiliary contact depends on the type of contact(s), and how
they are connected to the binary inputs:
•
Both “a” and “b” type auxiliary contacts are connected.
•
Only an “a” type auxiliary contact is connected.
•
Only a “b” type auxiliary contact is connected.
•
No auxiliary contact is connected.
The circuit breaker condition can be detected prior to the initiation of a trip signal, de-
pending on the configuration of binary inputs and auxiliary contacts. This information
can be used to properly operate the breaker failure function.
Logic
If breaker failure is initiated, an alarm message is generated (50 BF Pickup), and the
breaker failure timer is started. Once the time delay elapses, a breaker failure trip sig-
nal is issued (50 BF Trip). Figure 6-54 shows the logic diagram for the breaker failure
protection scheme. It is possible to turn the entire breaker failure protection function
on or off, or it can be blocked dynamically via binary inputs.
For utilities requiring a 50BF Retrip function, the 50BF Pickup element (internally and/
or externally initiated pickup) can be configured to the circuit breaker trip output con-
tact.
If one of the criteria (current value, breaker auxiliary contacts) that led to pickup of the
breaker failure scheme is no longer met during the time delay elapses, then breaker
failure timer drops out and no trip signals are issued.
To protect against nuisance tripping due to excessive contact bounce, a stabilization
of the binary inputs for external trip signals takes place. This external signal must be
present during the entire period of the delay time, otherwise the timer is reset and no
tripping signal is issued.
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