The method of conducting AC withstand voltage test withvariable frequency series resonance test deviceis to change the inductance and frequency in the test circuit to make the circuit in resonance state. This method can meet the test requirements of high voltage and high current. When using thevariable frequency series resonance test devicefor AC withstand voltage test, 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 defects or abnormalities, the test should be conducted after cleaning.
(2) Adjust the gap between the protective balls to a discharge voltage of 105% to 110% of the test voltage. Test three times in a row, there should be no significant difference, and check the reliability of the overcurrent protection device operation.
(3) In the experiment, if it is found that the pointer of the voltmeter swings greatly and the test substance makes abnormal noises. When the indication of the milliampere meter rapidly increases, and the test substance emits smoke, fire, or continuous spark discharge on the insulation surface. The voltage should be immediately lowered, and after hanging a ground wire on the high voltage side, the cause should be identified.
(4) The test site of the variable frequency series resonance test device should be fenced off. Hang up warning signs. And assign a dedicated person to supervise.
(5) After connecting the wires according to the test wiring diagram, a dedicated person should check and confirm that there are no errors. Including the distance between the lead wire and the ground, safety distance, etc., and preparation for pressurization can be carried out afterwards.
(6) Before applying pressure, check if the regulator is in the zero position and confirm that it is in the zero position before applying pressure. And the operation should only be carried out after shouting 'increase the pressure'.
(7) Before the experiment, the insulation surface of the tested equipment should be wiped clean, and the outer shell of the test equipment, the tested sample, and the non tested winding should be reliably grounded. For multi oil equipment, the oil should be allowed to stand still for a certain period of time according to relevant regulations before conducting the experiment. For example, for large capacity transformers, the oil should be kept still for 12-24 hours, and for 3-10 kV transformers, the oil should be kept still for 6-12 hours.
(8) During the boosting process, the changes in the voltmeter and other instruments should be monitored, and the capacitance current of the tested equipment should be read at 0.5 times the additional test voltage. When the additional voltage is raised, start calculating the time, then read the capacitor current, slowly drop the voltage to zero after the time is up, and then disconnect the power supply.
(9) Regarding the boost speed, it can be slightly faster when the test voltage is below 30%. Afterwards, the boost should be uniform, with a boost of approximately 5% of the test voltage per second, or an additional test voltage of 10-15 seconds.
(10) The tested equipment has no clear regulations, and the general withstand voltage time is 1 minute. The withstand voltage time of insulating rods and other tools is 5 minutes, and the ground wire should be hung in a timely manner after the test is completed. Then contact the relevant parts and there should be no heating phenomenon;
(11) Before and after the experiment, the insulation resistance and absorption ratio of the tested equipment should be measured. The results of the two measurements should not be significantly different.
