MA-037 - CB Watch 3 Operating Manual
v7.0 - May 2020
Page 72 of 118
A small degradation of the coil can therefore be detected before it becomes problematic
and the coil becomes open circuit, preventing the open/trip or close command from the
protection relay being executed.
The following information is displayed in the HMI:
HMI: Measurement / Last opening results or last closing results
Figure 112
–
Coil currents and coil charges
Values are displayed for each pole, for the opening coils being used (open1 or open2) and
for the closing coils:
•
The “
Mean coil current
” is the average level of the coil current during the operations
•
The
“C
oil actuation charge
”
is a measure used to reflect both coil current and
actuation time, it is the area under the
“
coil current
/vs/ time”
curve and is the
integration of the current multiplied by the time (A x ms).
The diagram below shows that the coil actuation charge can be longer (green curve) if the
latch is sticking for example and the CB does not start moving as early as on the pink normal
curve. A damage coil will also show a higher current and a longer coil charge.
Figure 113
–
Change in coil charge
Please note that in some protection schemes, both the opening 1 and backup opening 2
relays are fired “simultaneously” rather than only if the other one fails to open the breaker.
In this case, it is impossible to predict which of the relay will operate which pole of the
circuit breaker. The CBW3 system determines which signals it receives first and displays the
corresponding current value. So please be aware that we could end up with different poles
