Siemens siprotec 7SD5 User Manual page 370

2 Functions
3905). Be sure that the correct trip commands are assigned to the desired trip re-
lay(s).
The delay times are determined from the maximum operating time of the feeder circuit
breaker, the reset time of the current detectors of the breaker failure protection, plus a
safety margin which allows for any tolerance of the delay timers. Figure 2-160 illus-
trates the timing of a typical breaker failure scenario. The dropout time for sinusoidal
currents is ≤ 15 ms. If current transformer saturation is anticipated, the time should be
set to 25 ms.
Figure 2-160
Circuit Breaker not If the circuit breaker associated with the feeder is not operational (e.g. control voltage
Operational 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 adjacent breakers (bus-bar trip).
The end fault protection can be switched separately ON or OFF in address 3921 End
End Fault
Flt. stage. An end fault is a short-circuit between the circuit breaker and the current
Protection
transformer set of the feeder. The end fault protection presumes that the device is in-
formed 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 bus-bar protection (the fault is a bus-bar 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 con-
dition of the feeder protection, the circuit breaker auxiliary contacts indicate open poles
and, at the same time, current flow is still detected (address 3902). The trip command
of the end fault protection is intended for the transmission of an intertrip signal to the
remote end circuit breaker.
Thus, the delay time must be set such that it can bridge out short transient apparent
stub fault conditions which may occur during switching of the breaker.
370
Time sequence example for normal clearance of a fault, and with circuit breaker
failure, using single-stage breaker failure protection
7SD5 Manual
C53000-G1176-C169-1