Coil Continuity; Setting Alarms; Figure 122 - Coil Circuit Continuity Alarm - GE CSE Uniserve CB Watch 3 Operating Manual

Coil Continuity

This is about continuously monitoring the continuity of the open/trip and close coil outside
of when an operation is occurring. This is because there is no current flowing through the
coil when no operation is taking place and therefore the coil current cannot be measured
continuously.
This is a more basic functionality than coil current measurements as it is all or nothing and
only detects when the coil has gone open circuit, not when it is deteriorating.
While some modern relays already provide this functionality by continually checking the
continuity of the control circuit, including the coil, this is not always the case, especially in
older sub-stations with older relays.
If present, the optional TCW continuity monitoring sensor injects a small current in the
control line at either side of each coil, below the level needed to actuate the coil, in order to
continually check that the coil is not open circuit.
The sensor has 3 channels and returns a digital true/false signal as to the good state of the
coil. If at least one coil goes open for >10s, then an alarm is raised and displayed in the HMI:
HMI: Measurements / Alarms

Setting Alarms

Notice: It is the customer's responsibility to decide whether to set alarms or not and to
decide what thresholds to set alarms at, as this will depend on the customer's operational
priorities and risk philosophy. However, here are some guidelines that may prove helpful in
deciding what threshold values to use:
Alarm summary
This table summarises all the alarms that can be set for control circuit monitoring:
MA-037 - CB Watch 3 Operating Manual
Figure 122 – Coil circuit continuity alarm
v7.0 - May 2020 Page 76 of 118