Siemens siprotec 7SA6 User Manual page 419

End Fault
Protection
7SA6 Manual
C53000-G1176-C133-1
An end fault is defined here as a short–circuit which has occurred at the end of a line
or protected object, between the circuit breaker and the current transformer set.
This situation is shown in Figure 6-124. The fault is located — as seen from the current
transformers (= measurement location) — on the bus-bar side, thus, it will not be
regarded by the feeder protection relay as a feeder fault. It can only be detected by
either a reverse stage of the feeder protection or by a bus-bar protection.
Nevertheless, a trip command given to the feeder circuit breaker cannot clear the fault
since the opposite end(s) continue(s) to feed the fault. Thus, the fault current does not
stop flowing even though the feeder circuit breaker has properly responded to the trip
command.
Feeder
Figure 6-124 End fault between circuit breaker and current transformers
The end fault protection has the task to recognize this situation and to transmit a trip
signal to the remote end(s) of the protected object to clear the fault. For this purpose,
the output command "%) (QG)OW 75,3" is available to trigger a signal transmission
device (e.g. power line carrier, radio wave, or optical fibre) — if applicable, together
with other commands that need to be transferred.
The end fault is recognized when the current continues flowing although the circuit
breaker auxiliary contacts indicate that the breaker is open. In the 7SA6, an additional
criterion is the presence of any breaker failure protection initiate signal. The scheme
functionality is shown in Figure 6-125. If the breaker failure protection is initiated and
current flow is recognized (current criteria "L
breaker pole is closed (auxiliary contact criterion "CB any pole closed"), then a timer
7(QG)DXOW is started, after which an intertrip signal is transmitted to the opposite
end(s) of the protected object.
L1>
> 1
L2>
L3>
FNo 1461
BF Start
CB any pole closed
Figure 6-125 Function block diagram of end fault protection
Bus-bar
Trip by
protection
I
SC
∗
>" according Figure 6-113), but no circuit
3922
&
T
&
Functions
T-ENDFault
FNo 1495
0
BF EndFlt TRIP
6-237