Functions
2.24 Monitoring Functions
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
441
Figure 2-216 Principle of the trip circuit supervision with one binary input
TR Trip relay contact
CB Circuit breaker
TC Circuit breaker trip coil
Aux1 Circuit breaker auxiliary contact (NO contact)
Aux2 Circuit breaker auxiliary contact (NC contact)
U-CTR Control voltage for trip circuit
U-BI Input voltage of binary input
R Bypass resistor
UR Voltage across the bypass resistor
During normal operation, the binary input is activated (logical condition „H“) when the trip contact is open and
the trip circuit is intact, because the supervision circuit is closed either by the circuit breaker auxiliary contact
(if the circuit breaker is closed) or through the bypass resistor R. Only as long as the trip contact is closed, the
binary input is short-circuited and thereby deactivated (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.
The trip circuit supervision does not operate during system faults. A momentary 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 2-217). After clearance
of the failure in the trip circuit, the fault message automatically resets with the same time delay.
Figure 2-217 Logic diagram for trip circuit supervision with one binary input
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