Breaker Failure Protection 50Bf; Description - Siemens SIPROTEC 7SK80 Manual
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2.12
Breaker Failure Protection 50BF
The breaker failure protection function monitors proper tripping of the relevant circuit breaker.
2.12.1
Description
General
If after a programmable time delay, the circuit breaker has not opened, breaker failure protection issues a trip
signal to isolate the failure breaker by tripping other surrounding backup circuit breaker (see example in the
figure below).
Figure 2-72
Initiation
The breaker failure protection function can be initiated by two different sources:
• Trip signals of internal protective functions of the 7SK80,
• external trip signals via binary inputs („>50BF ext SRC").
For each of the two sources, a unique pickup message is generated, a unique time delay is initiated, and a
unique trip signal is generated. The setting values of current threshold and delay time apply to both sources.
Criteria
There are two criteria for breaker failure detection:
• Check whether the current flow has effectively disappeared after a tripping command was issued,
• Evaluate the circuit breaker's auxiliary contacts.
The criteria used to determine if the circuit breaker has operated are selectable and also depend on the pro-
tection function that initiated the breaker failure function. On tripping without fault current, e.g. via voltage pro-
tection, the current below the threshold 50BF PICKUP is not a reliable indication of the proper functioning of
the circuit breaker. In such cases, pickup exclusively depends on the auxiliary contact criterion. In protection
functions based on the measurement of currents (including all short-circuit protection functions), the current
flow is a preferential criterion, i.e. it is given priority, as opposed to the auxiliary contacts. If current flows above
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
Function principle of the breaker failure protection
Functions
2.12 Breaker Failure Protection 50BF
199
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