2 Functions
172
7ST6 Manual
E50417-G1176-C251-A3
Figure 2-51
Principle of trip circuit monitoring with one binary input
In normal operation, the binary input is energized when the trip relay contact is open
and the trip circuit is healthy (logic state „H“), as the monitoring circuit is closed via the
auxiliary contact (if the circuit breaker is closed) or via the substitute resistor R. Only
as long as the trip contact is closed, the binary input is short circuited and thereby de-
activated (logical condition „L“).
If the binary input is permanently deactivated during operation, an interruption in the
trip circuit or a failure of the (trip) control voltage can be assumed.
Because the trip circuit supervision does not operate during system faults, a closed
tripping contact does not lead to a fault indication. If however other trip relay contacts
from different devices are connected in parallel in the trip circuit, the fault indication
must be delayed by
Alarm Delay
(see also Figure 2-52). After the fault in the trip
circuit is removed, the indication is reset automatically after approx. 1.5 s.
Figure 2-52
Logic diagram of trip circuit monitoring with one binary input
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