7.1 Trip circuit supervision
7 Application
Technical description
140
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VM55.EN005
7.1.1.
Trip circuit supervision with one digital input
The benefits of this scheme is that only one digital inputs is
needed and no extra wiring from the relay to the circuit
breaker (CB) is needed. Also supervising a 24 Vdc trip circuit is
possible.
The drawback is that an external resistor is needed to
supervise the trip circuit on both CB positions. If supervising
during the closed position only is enough, the resistor is not
needed.
The digital input is connected parallel with the trip contacts
(Figure 7.1.1-1).
The digital input is configured as Normal Closed (NC).
The digital input delay is configured longer than maximum
fault time to inhibit any superfluous trip circuit fault alarm
when the trip contact is closed.
The digital input is connected to a relay in the output
matrix giving out any trip circuit alarm.
The trip relay should be configured as non-latched.
Otherwise, a superfluous trip circuit fault alarm will follow
after the trip contact operates, and the relay remains closed
because of latching.
By utilizing an auxiliary contact of the CB for the external
resistor, also the auxiliary contact in the trip circuit can be
supervised.
