7 TRIP CIRCUIT SUPERVISION
In most protection schemes, the trip circuit extends beyond the IED enclosure and passes through
components such as links, relay contacts, auxiliary switches and other terminal boards. Such complex
arrangements may require dedicated schemes for their supervision.
There are two distinctly separate parts to the trip circuit; the trip path, and the trip coil. The trip path is the
path between the IED enclosure and the CB cubicle. This path contains ancillary components such as
cables, fuses and connectors. A break in this path is possible, so it is desirable to supervise this trip path and
to raise an alarm if a break should appear in this path.
The trip coil itself is also part of the overall trip circuit, and it is also possible for the trip coil to develop an
open-circuit fault.
7.1 TRIP CIRCUIT SUPERVISION SCHEME 1
This scheme provides supervision of the trip coil with the CB open or closed, however, it does not provide
supervision of the trip path whilst the breaker is open. Also, the CB status can be monitored when a self-
reset trip contact is used. However, this scheme is incompatible with latched trip contacts, as a latched
contact will short out the opto-input for a time exceeding the recommended Delayed Drop-off (DDO) timer
setting of 400 ms, and therefore does not support CB status monitoring. If you require CB status monitoring,
further opto-inputs must be used.
Note:
A 52a CB auxiliary contact follows the CB position. A 52b auxiliary contact is the opposite.
V01214
52A
52B
R
1
Trip Output Relay
+
ve
-ve
Opto-input
B
locking diode
Circuit Breaker
Trip coil
Trip path
Figure 41: TCS Scheme 1
When the CB is closed, supervision current passes through the opto-input, blocking diode and trip coil. When
the CB is open, supervision current flows through the opto-input and into the trip coil via the 52b auxiliary
contact. This means that Trip Coil supervision is provided when the CB is either closed or open, however
Trip Path supervision is only provided when the CB is closed. No supervision of the trip path is provided
whilst the CB is open (pre-closing supervision). Any fault in the trip path will only be detected on CB closing,
after a 400 ms delay.
Chapter 6 - Monitoring and Control MiCOM P747
188 P747-TM-EN-1
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