MA-037 - CB Watch 3 Operating Manual
v7.0 - May 2020
Page 63 of 118
Arcing Time
Arcing time measurement
During an open operation, we are particularly interested in the “Arcing time”. To calculate
that, we need to know when the arcing starts (as we know when it finishes when the
interrupted current goes to zero).
When there is a travel sensor present, we can determine exactly when the arcing contacts
have physically separated (ts). We know the physical distance and know when it has been
reached and therefore exactly when the arcing begins.
When a travel sensor is not present, we must estimate when the arcing begins. From the CB
FAT and type tests, we know the original time-offset between when the CB starts to open
(52a) and when the arcing contacts physically separate. We must rely on this separation
time offset (ts-t1) which we input during the setup based on FAT measurement data from
the manufacturer of the CB. It can be set differently per pole but is usually the same.
HMI: Settings / Opening
Figure 92
–
Separation offset input
Figure 93
–
Opening operation timing diagram
The “end of arcing” (ta) is the time when the current flow stops for that pole. This is deemed
to have happened when 10 consecutive values (one every 0.4ms) of the current for that
pole are less than Z, where Z
, the “zero current level”,
is equal to 10% of the absolute value
of the largest Imax or Imin recorded for that pole during the first 20 milliseconds of the
opening operation.
