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Figure 2-70
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 monitoring circuit is closed
by either 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 continuously deactivated during operation, this leads to the con-
clusion that there is an interruption in the trip circuit, or a loss of (tripping) control volt-
age.
Because the trip circuit monitor does not operate during system faults, a closed trip-
ping contact does not lead to a fault message. If, however, tripping contacts from other
devices operate in parallel with the trip circuit, then the fault annunciation must be
delayed (see also the following figure). The conditions of the binary input are therefore
checked 500 times before an annunciation is issued. A condition check takes place
about every 600 ms, so trip circuit monitoring is only activated during an actual mal-
function of the trip circuit (after 300 s). After the fault in the trip circuit is removed, the
alarm is reset automatically after the same time.
Note
If the lock-out function is used, the trip circuit monitoring with only one binary input
must not be used, as the relay remains permanently picked up after a trip command
(longer than 300s).
Figure 2-71
7UM61 Manual
C53000-G1176-C127-3
Principle of Trip Circuit Monitoring with One Binary Input
Logic diagram for Trip Circuit Monitoring with one binary input
2.29 Trip Circuit Supervision
179
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