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Technical description
7 Applications
7.4 Trip circuit supervision
VM259.EN007
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7.4.
Trip circuit supervision
Trip circuit supervision is used to ensure that the wiring from
the protective device to a circuit-breaker is in order. This
circuit is unused most of the time, but when a protection device
detects a fault in the network, it is too late to notice that the
circuit-breaker cannot be tripped because of a broken trip
circuitry.
The digital inputs of the device can be used for trip circuit
monitoring. The dry digital inputs are most suitable for trip
circuit supervision. The first six digital inputs of VAMP 200
series relays are not dry and an auxiliary miniature relay is
needed, if these inputs are used for trip circuit supervision.
Also the closing circuit can be supervised, using the same
principle.
The optimum digital inputs for trip circuit supervision are
inputs DI29 …DI32, which are internally wired in parallel
within trip relays T5 … T8. These inputs are not sharing the
common terminal with others inputs.
7.4.1.
Internal parallel digital inputs
In VAMP 259-3C7 and VAMP 259-3C8, the output relays T5
(DI29), T6(DI30), T7(DI31) and T8(DI32) have internal,
parallel digital inputs available for trip circuit supervision.
7.4.2.
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 7.4.2-1).
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.