Frequently asked
- C–O (Close–Open) test settings
On our high-voltage switch analyzer the “C–O control time” is the interval between the rising edge of the CLOSE command pulse and the rising edge of the OPEN command pulse (in a reclosing sequence it is the instant when the second OPEN pulse is issued).
Factory default = 120 ms; this must be changed for every breaker type.
Recommended first choice:
C–O control time = measured close time + T (5 ms ≤ T ≤ 20 ms)
Set the value to 0 ms if you need the minimum achievable C–O time (metal-clad time).
With 0 ms the two pulses are issued simultaneously; the breaker’s auxiliary contact must interrupt the close coil circuit and transfer to the open coil. Some breakers cannot tolerate this and may show insufficient opening energy, longer opening time, lower speed, etc.
Caution: when C–O control = 0 the pulses remain active for the whole test duration; be sure to:
- limit the total test time, or
- rely on the breaker’s anti-pump relay,
otherwise the breaker will close again after the first C–O cycle.
Typical target: most manufacturers specify a C–O time ≈ 60 ms.
Protection relays need ≥ 10 ms to acquire data plus calculation and output-relay pick-up; therefore issuing the open pulse 20 ms after contact make is normally acceptable.
- O–C–O (Open–Close–Open) control settings
The “dead time” (no-current interval) is required to be 300 ms.
Calculate:
O–C control time = measured open time + 300 ms – measured close time
(both times come from single C and single O tests).
The second C–O control time inside the O–C–O sequence is set in exactly the same way as described in section 1.