CB Watch 3 User Manual
v6.3 - May 2019
Page 50 of 100
During the first 20 milliseconds following the command to the coil, the minimum and
maximum peak current values (Imin and Imax) are determined. The value of the
interrupted current is made using the equation: Irms=(Imax-Imin)/2
2.
This RMS interrupted current value for each pole is displayed in the HMI:
HMI: Measurements / last opening results
Figure 70
–
Interrupted current value
A simplified current curve is displayed and archived with each operation (1 point every
400 micro seconds).
HMI: Measurements / Operations charts / Opening
Figure 71
–
Stored interrupted current curve
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 that it finishes when the
interrupted current CTs show a measured value of 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
