2 Functions
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7SA522 Manual
C53000-G1176-C155-3
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 2-129). The phase-segre-
gated 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 or three-pole trip it is possi-
ble to use the timer stages 7SROH and 7SROH according to Figure 2-130.
Figure 2-129 Single-stage breaker failure protection with common phase initiation
Figure 2-130 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, a different time delay 7SROH can be selected for a single-
pole trip than for a 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.
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