CB Watch 3 User Manual
v6.3 - May 2019
Page 61 of 100
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.
With the appropriate sensors installed, the 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 opens for >10s, then an alarm is raised and is displayed
in the HMI:
HMI: Measurements / Alarms
Figure 96
–
HMI - Coil circuit continuity alarm