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TEST PROCEDURE:
1. The circuit breaker should be disconnected from the main circuit and be in the OFF position.
2. Connect all the line side primary terminals together and to the output of the vacuum checker or AC
hi-pot machine. Connect all the load side primary terminals together and to the ground terminal of
the vacuum checker or AC hi-pot machine.
3. Increase the voltage from zero to 22kV AC at a rate of approximately 2kV per second. Hold the
voltage at this value for 1 minute and observe the current drawn by the interrupter.
Note: If the ammeter fluctuates violently as the voltage increases to AC22 kV, repeat the
voltage increase procedure two or three times. If the current still rises when the voltage is
increased, the vacuum level may be insufficient;
replace the vacuum interrupter.
4. Decrease the voltage back to zero.
CRITERIA:
1. If a current flow above 5 milliamperes is observed or
if breakdown occurs, one or more of the interrupters
has insufficient vacuum and must be replaced.
Exception: If the current exceeds 5 milliamperes the
first time the voltage is brought up, reduce the
voltage to zero and increase it again. It may be
necessary to repeat this procedure a few times.
2. If the breaker fails to meet criteria 1, then repeat the
test on each pole separately to identify the damaged
interrupter or interrupters.
3. If the voltage can be held for 1 minute and the current flow does not exceed 5 milliamperes, the
interrupter has a sufficient vacuum level.
After the test is complete, discharge any residual static charge from the primary terminals of the circuit
breaker.
If a vacuum checker or AC hi-pot tester is not available, a DC hi potential test may be conducted. If a DC
test is conducted, the test voltage must be increased to 31kV DC. The test duration for DC tests and the
criteria for acceptance remain the same as for AC tests.
Do not use DC hi-pot testers which employ unfiltered half-wave rectifiers.
The peak voltages produced by these testers may exceed the recommended
value of 31kV. This can result in the production of harmful X-rays
and may invalidate the test results.
1 minute
22kV AC
(31kV DC)
Voltage
Zero
15 sec 15 sec
Time
Figure 24 Application of Test
Voltage for Vacuum Check
WARNING