The method of measuring AC withstand voltage through series resonance is to change the inductance and frequency in the test circuit, and the circuit is in a resonant state. This method can meet the testing requirements of high voltage and high current. When conducting series resonant AC withstand voltage tests, the following points should be noted:

1. Before the experiment, it is necessary to understand whether the non-destructive testing items of the tested equipment are qualified. If there are any defects or abnormalities, they should be tested after being eliminated.

2. The experimental site should be enclosed, warning signs should be hung, and a dedicated person should be present for supervision;

3. The insulation surface of the equipment to be tested should be cleaned before the test, and the test equipment, test object casing, and non test winding should be reliably grounded. For multi oil equipment, the test should be conducted after the oil has been stationary for a certain period of time according to relevant regulations. For example, for large capacity transformers, the oil should be left to stand for 12-24 hours; For 3-10kV transformers, the oil should be left to stand for 6-12 hours;

4. Adjust the gap between the protective balls to achieve a discharge voltage of 105% to 110% of the test voltage, and conduct three consecutive tests. There is no significant difference, check the reliability of the overcurrent protection device operation;

5. After wiring according to the test wiring diagram, a dedicated person should check and confirm that there are no errors (including grounding distance, safety distance, etc.) before preparing for pressurization;

6. Before applying pressure, check if the pressure regulator is in the zero position. Confirm that the pressure regulator is in the zero position before applying pressure, and only operate when it is high;

7. For the boosting speed, when the test voltage is less than 30%, it can be slightly faster, and then the boosting should be uniform, about 5% of the test voltage, or 10-15 seconds when the rated test voltage rises;

8. During the boosting process of the series resonant device, monitor the changes in the voltmeter and other instruments. When the rated voltage is 0.5 times, read the capacitance current of the tested equipment. When the voltage rises to the rated voltage, start calculating the time. Then read the current of the capacitor, slowly reduce the voltage to zero after time, and then disconnect the power supply;

9. In the experiment, if it is found that the pointer of the voltmeter swings greatly, there is abnormal noise from the test sample, the milliampere meter reading increases sharply, the test sample smokes or catches fire, and continuous spark discharge occurs on the insulation surface. The voltage should be immediately reduced, and the cause should be identified after hanging a grounding wire on the high-voltage side;

10. If the tested equipment is not specified, the general voltage withstand time is 1 minute, and the withstand time of insulation rods and other electrical appliances is 5 minutes. After the experiment is completed, hang the grounding wire in a timely manner and then contact the relevant components without heating;

11. The insulation resistance and absorption rate of the tested equipment should be measured before and after the test, and the results of the two measurements should not be significantly different.