Circuit Breaker Failure Protection
The circuit breaker failure protection provides rapid back-up fault clearance, in the event that the assigned
circuit breaker fails to respond to a protective relay.
7UT612 is equipped with one, 7UT613/63x with two breaker failure protection functions that can be used
independently of each other and for different locations of the protected object, i.e. for different circuit
breakers. You can also work with different starting criteria (see below). Allocation of the protective function to
the sides or measuring locations and breakers were done according to Section 2.1.4 Power System Data 1.
Functional Description
General
The following information refers to the first breaker failure protection, if not stated otherwise.
Whenever the differential protection or any internal or external fault protection function of a feeder issues a
trip command to the circuit breaker, for example, this is indicated to the breaker failure protection at the same
time (Figure 2-109). A timer T– BF in the breaker failure protection is started. The timer runs as long as a trip
command is present and current continues to flow through the breaker poles.
[lsversagerschutz-funktionsschema-020926-rei, 1, en_GB]
Figure 2-109
Simplified function diagram of circuit breaker failure protection with current flow monitoring
Normally, the breaker will open and interrupt the fault current. The current monitoring stage BF-Ι> quickly
resets (typically
1
/
2
AC cycle) and stops the timer T-BF.
If the trip command is not executed (in case of breaker failure), current continues to flow and the timer runs
to its set limit. The breaker failure protection then issues a command to trip the backup breakers which inter-
rupt the fault current.
The reset time of the starting protection functions is not relevant because the breaker failure protection itself
recognises the interruption of the current.
2.17
2.17.1
Functions
2.17 Circuit Breaker Failure Protection
244 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
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