Circuit breaker failure protection (optional)
The circuit breaker failure protection provides rapid back-up fault clearance in the event that the circuit
breaker fails to respond to a trip command from a protection function of the local circuit breaker.
Functional Description
General
Whenever e.g. a short-circuit protection relay of a feeder issues a trip command to the circuit breaker, this is
repeated to the circuit breaker failure protection (Figure 2-31). A timer T–BF in the circuit breaker failure
protection is started. The timer runs as long as a trip command is present and current continues to flow
through the circuit breaker poles.
[funktionsschema-lvs-ueberwach-wlk-010802, 1, en_GB]
Figure 2-31 Simplified function diagram of circuit breaker failure protection with current flow monitoring
Normally, the circuit breaker will open and interrupt the fault current. The current monitoring stage quickly
resets (typical 10 ms) and stops the timer T–BF.
If the trip command is not carried out (circuit breaker failure case), current continues to flow and the timer
runs to its set limit. The circuit breaker failure protection then issues a command to trip the backup circuit
breakers and interrupt the fault current.
The reset time of the feeder protection is not relevant because the circuit breaker failure protection itself
recognizes the interruption of the current.
For protection functions where the tripping criterion is not dependent on current (e.g. Buchholz protection),
current flow is not a reliable criterion for proper operation of the circuit breaker. In such cases, the circuit
breaker position can be derived from the auxiliary contacts of the circuit breaker. Therefore, instead of moni-
toring the current, the position of the auxiliary contacts is monitored (Figure 2-32). For this purpose, the
outputs from the auxiliary contacts must be fed to binary inputs on the relay (refer also to Section 2.8.1 Func-
tion Control).
2.6
2.6.1
Functions
2.6 Circuit breaker failure protection (optional)
SIPROTEC 4, 7VK61, Manual 115
C53000-G1176-C159-5, Edition 05.2018
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