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Functions
2.22 Circuit Breaker Failure Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
411
End fault protection
The end fault protection can be switched separately ON or OFF in address 3921 End Flt. stage . An end
fault is a short-circuit between the circuit breaker and the current transformer set of the feeder. The end fault
protection presumes that the device is informed about the circuit breaker position via circuit breaker auxiliary
contacts connected to binary inputs.
If, during an end fault, the circuit breaker is tripped by a reverse stage of the feeder protection or by the busbar
protection (the fault is a busbar fault as determined from the location of the current transformers), the fault
current will continue to flow, because the fault is fed from the remote end of the feeder circuit.
The time T-EndFault (address 3922 ) is started when, during the time of pickup condition of the feeder pro-
tection, the circuit breaker auxiliary contacts indicate open poles and, at the same time, current flow is still de-
tected (address
3902 ). The trip command of the end fault protection is intended for the transmission of an in-
tertrip signal to the remote end circuit breaker.
Thus, the delay time must be set so that it can bridge out short transient apparent end fault conditions which
may occur during switching of the circuit breaker.
Pole discrepancy supervision
In address 3931 PoleDiscrepancy (pole discrepancy protection), the pole discrepancy supervision can be
switched separately ON or OFF . It is only useful if the circuit breaker poles can be operated individually. It avoids
that only one or two poles of the local circuit breaker are open continuously. It has to be provided that either the
auxiliary contacts of each pole or the series connection of the NO auxiliary contacts and the series connection
of the NC auxiliary contacts are connected to the device's binary inputs. If these conditions are not fulfilled,
switch address
3931 OFF .
The delay time T-PoleDiscrep. (address 3932 ) indicates how long a circuit breaker pole discrepancy con-
dition of the feeder circuit breaker, i.e. only one or two poles open, may be present before the pole discrepancy
supervision issues a 3-pole trip command. This time must be clearly longer than the duration of a 1-pole auto-
matic reclose cycle. The time should be less than the permissible duration of an unbalanced load condition
which is caused by the unsymmetrical position of the circuit breaker poles. Conventional values are 2 s to 5 s.