Siemens siprotec 7SD5 User Manual

2 Functions
360
7SD5 Manual
C53000-G1176-C169-1
Figure 2-145 Current flow monitoring with plausibility currents 3·I
0
and 3·I
2
Processing of the
Circuit Breaker
Auxiliary Contacts
The position of the circuit breaker is derived from the central function control of the
device (refer also to Section 2.23.1). Evaluation of the breaker auxiliary contacts is
carried out in the breaker failure protection function only when the current flow moni-
toring has not picked up. Once the current flow criterion has picked 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) indi-
cate that the circuit breaker has opened (Figure 2-146). This gives preference to the
more reliable current criterion and avoids overfunctioning due to a defect e.g. in the
auxiliary contact mechanism or circuit. This interlock feature is provided for each indi-
vidual phase as well as for three-pole trip.
It is possible to disable the auxiliary contact criterion. If you set the parameter switch
Chk BRK CONTACT (Figure 2-148 top) to NO, 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.
Figure 2-146 Interlock of the auxiliary contact criterion - example for phase L1
On the other hand, current flow is not a reliable criterion for proper operation of the
circuit breaker for faults which do not cause detectable current flow (e.g. Buchholz pro-
tection). Information regarding the position of the circuit breaker auxiliary contacts is
required in these cases to check the correct response of the circuit breaker. For this
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Siemens siprotec 7SD5 Specifications

General

Brand	Siemens
Model	siprotec 7SD5
Category	Relays
Language	English