Siemens SIPROTEC 7SA6 Manual page 448

Distance protection relay for all voltage levels

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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 6-133. The fault is located — as seen from the current

transformers (= measurement location) — on the bus-bar side, thus, it will not be re-

garded 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 oppo-

site 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.

Figure 6-133 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 " BF EndFlt TRIP " 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 6-134. 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

T-EndFault is started, after which an intertrip signal is transmitted to the opposite

end(s) of the protected object.

CB any pole closed

Figure 6-134 Function block diagram of end fault protection

>" according Figure 6-122), but no circuit

BF EndFlt TRIP

C53000-G1176-C156-2