AC withstand voltage test of high-voltage circuit breaker
The AC withstand voltage test of circuit breakers is the most effective and direct test item for evaluating the insulation strength of circuit breakers. This test should be conducted after all other insulation tests have been completed. For filtered and newly filled circuit breakers, they usually need to be left to stand for about 3 hours to allow all the air bubbles in the oil to escape before the test can be carried out. Gas circuit breakers should undergo the test under a lower allowable pressure to easily detect internal insulation defects.
The test voltage for the withstand voltage test is generally generated by a test transformer or a variable-frequency series resonance circuit. To ensure that the test voltage is not affected by changes in leakage current, the short-circuit current of the tested item delivered by the transformer should be no less than 0.1A. When the tested item discharges, causing significant fluctuations in the test voltage, it may result in damage to the tested item and the test transformer. Therefore, some damping elements should be connected in series in the test circuit.
The variable frequency series resonant circuit mainly consists of a capacitive test sample or load, an inductor in series with it, and a medium-voltage power supply. It can also be formed by connecting a capacitor in series with a capacitive test sample. By changing the circuit parameters or the power supply frequency, the circuit resonates, generating an amplitude much greater than the medium-voltage power supply voltage that is applied to the test sample. When the test sample discharges, due to the relatively small current output by the power supply, the damage to the insulation of the test sample is limited.
Intelligent frequency tuning can either automatically tune and scan the resonant frequency, or it can be manually searched. When the system automatically scans, it automatically sweeps the frequency from 30Hz to 300Hz. After the scanning is completed, based on the initially found resonant frequency point through the scanning results, the system conducts a fine frequency sweep within a ±5Hz range with a resolution of 0.01Hz, and finally precisely locks onto the resonant frequency.
Once the system resonance frequency is determined, the equipment can automatically increase the voltage according to the pre-set segmented tests or single tests, complete the tests automatically, and record the test results. It can also be manually adjusted to conduct the withstand voltage test.
The AC withstand voltage test should be conducted separately in both the open and closed positions of the circuit breaker. For circuit breakers with a voltage rating of 12 to 40.5 kV and those with a three-phase enclosed structure, an inter-phase withstand voltage test should also be carried out. The test voltage value for this test is the same as that for the withstand voltage to ground. During the withstand voltage test, if the test sample does not experience flashover or breakdown, and does not heat up after the withstand voltage is applied, it is considered that the withstand voltage test has been passed.
For the AC withstand voltage test of the auxiliary circuit and control circuit of the circuit breaker, the test voltage is 2 kV.
Post time: Apr-21-2026