Siemens siprotec 7SA522, User Manual

Page: 350 / 628

Functions
6-202
7SA522 Manual
C53000-G1176-C119-2
Figure 6-99 Current flow monitoring with the plausibility currents 3· I
0
and 3· I
2
Processing of the
circuit breaker aux-
iliary contacts The position of the circuit breaker is derived from the central function control of the de-
vice (refer also to Section 6.14.2). Evaluation of the breaker auxiliary contacts is car-
ried out in the breaker failure protection function only when the current flow monitoring
has not picked up. Once the current flow criterion picks up during the trip signal from
the feeder protection, the circuit breaker is assumed to be open as soon as the current
disappears, even if the associated auxiliary contact does not (yet) indicate that the cir-
cuit breaker has opened (Figure 6-100). This gives preference to the more reliable cur-
rent criterion and avoids overfunctioning due to a defect e.g. in the auxiliary contact
mechanism or circuit. This interlock feature is provided for each individual phase as
well as for three-pole trip.
It is possible to disable the auxiliary contact criterion. If you set the parameter switch
&KN%5.&217$&7
(Figure 6-101 above) to
1R
, the breaker failure protection can
only be started when current flow is detected. The position of the auxiliary contacts is
then not evaluated even if the auxiliary contacts are connected to the device.
,!
&
,!
,!
&
&
&
&
&
> 1
> 1
> 1
Current
criterion
I
L1
I
L2
I
L3
> 1
,!
3I
2
,!
3I
0
,!%)
L1>
L2>
L3>
plausi-
bility