Siemens Siprotec 7VK61 Manual page 128

Functions
2.6 Circuit breaker failure protection (optional)
Figure 2-44
Circuit breaker not operational
If the circuit breaker associated with the feeder is not operational (e.g. control voltage failure or air pressure
failure), it is apparent that the local breaker cannot clear the fault. If the relay is informed about this disturbance
(via the binary input „>CB faulty"), the adjacent circuit breakers (busbar and remote end if applicable) are
tripped after the time T3-BkrDefective (address 3907) which is usually set to 0.
Address 3908 Trip BkrDefect. determines to which output the trip command is routed in the event that the
breaker is not operational when a feeder protection trip occurs. Select that output which is used to trip the ad-
jacent breakers (bus-bar trip).
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 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 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 breaker poles can be operated individually. It avoids that
only one or two poles of the local 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 breaker pole discrepancy condition of
the feeder circuit breaker, i.e. only one or two poles open, may be present before the pole discrepancy super-
128
Time sequence example for normal clearance of a fault, and with circuit breaker failure, using
single-stage breaker failure protection
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009