Siemens siprotec 7SA6 User Manual page 417

7SA6 Manual
C53000-G1176-C133-1
Different delay timers are provided for operation after common phase initiation and
phase segregated initiation. A third time stage can be used for two-stage breaker
failure protection.
With single-stage breaker failure protection, the trip command is routed to the adjacent
circuit breakers should the local feeder breaker fail (refer to Figure 6-111 or 6-112).
The adjacent circuit breakers are all those which must trip in order to interrupt the fault
current, i.e. the breakers which feed the bus-bar or the bus-bar section to which the
feeder under consideration is connected. The possible initiation conditions for the
breaker failure protection are those discussed above. Depending on the application of
the feeder protection, common phase or phase segregated initiation conditions may
occur. Tripping by the breaker failure protection is always three-pole.
The simplest solution is to start the delay timer 7 (Figure 6-120). The phase-
segregated initiation signals are omitted if the feeder protection always trips three-pole
or if the circuit breaker is not capable of single-pole tripping.
If different delay times are required after a single-pole trip and three-pole trip by the
feeder protection it is possible to use the timer stages 7SROH and 7SROH
according to Figure 6-121.
Start only L1
Start only L2
> 1
Start only L3
Start L123
Figure 6-120 Single-stage breaker failure protection with common phase initiation
Start only L1
> 1
Start only L2
Start only L3
Start L123
Figure 6-121 Single-stage breaker failure protection with different delay timers
With two-stage breaker failure protection, the trip command of the feeder protection is
usually repeated, after a first time stage, to the feeder circuit breaker, often via a
second trip coil or set of trip coils, if the breaker has not responded to the original trip
command. A second time stage monitors the response to this repeated trip command
and trips the breakers of the relevant bus-bar section, if the fault has not yet been
cleared after this second time.
For the first time stage, different time delays can be selected for a single-pole trip and
three-pole trip by the feeder protection. Additionally, you can select (parameter S
5(75,3 7 ) whether this repeated trip should be single-pole or three-pole.
"(% U!
UÃÃÃÃÃÃ
"(# U  Q‚yr
UÃÃÃÃÃÃ
> 1
"($ U "Q‚yr
UÃÃÃÃÃÃ
Functions
(Trip
bus-bar)
FNo 1494
BF T2-TRIP(bus)
(Trip
bus-bar)
FNo 1476
BF T1-TRIP L123
6-235