The AC withstand voltage test applies an AC test voltage to the insulation of electrical equipment. This test voltage is higher than the equipment’s rated value. The AC withstand voltage test is a type of test where the working voltage is relatively high and lasts for a certain period of time (generally 1 minute), which is in line with the actual operating conditions of the electrical equipment. It is an important means to avoid insulation accidents. Therefore, the AC withstand voltage test is the most decisive test among all insulation tests.
However, the AC withstand voltage test also has its drawbacks. It is a destructive test. Moreover, at the test voltage, it can cause cumulative effects within the insulation. Therefore, the selection of the test voltage value is very cautious. The values chosen vary depending on the age of the equipment and the type of equipment. Relevant regulations have been made in China’s “Preventive Test Procedures for Electrical Equipment”.
The AC withstand voltage test can be classified into the following types:
Carry out alternating current withstand voltage test.
(2) 0.1 HZ test.
(3) Shock wave pressure resistance test.
(4) Frequency-doubled induced voltage test and operational wave test.
(5) Partial discharge test.
II. Experimental Precautions
This test can only be conducted after all the non-destructive tests of the test equipment have been passed. If there are any defects (such as moisture), the defects should be eliminated before proceeding with the test.
(2) The insulation surfaces of the test equipment should be wiped clean. For equipment with a lot of oil, the oil should be allowed to stand for a certain period of time.
(3) The voltage rise rate should be controlled. It can be faster before reaching 1/3 of the test voltage, and then it should be increased continuously at a rate of 3% of the test voltage per second until reaching the test voltage value.
(4) Before and after the experiment, the insulation resistance and absorption ratio should be compared. There should be no significant changes.
(5) The influence of humidity, temperature, and surface dirt should be excluded.
III. Operating Procedures
(1) Before conducting the test, it is necessary to verify whether the non-destructive test items of the tested object are qualified. Generally, the AC withstand voltage test should be carried out only after all non-destructive test items have been completed and passed. If there are any defects or abnormalities, they should be eliminated (such as drying when there is moisture) or resolved before the test can be conducted. The test site should be enclosed with barriers, signs should be hung, and a dedicated person should be assigned to monitor.
(2) Before the test, the insulating surface of the tested equipment should be wiped clean.
(3) For equipment with multiple oils, it is necessary to allow the oil to stand for a certain period of time as per relevant regulations. For example, for large-capacity transformers, the oil should be left to stand for 12 to 20 hours; for 3 to 10 kV transformers, the oil should be left to stand for 5 to 6 hours before conducting tests.
(4) Adjust the protective gap so that its discharge voltage is 105% to 110% of the test voltage. Conduct the test three times consecutively. There should be no significant differences, and check the reliability of the overcurrent protection device’s operation.
(5) After connecting the wires according to the test wiring diagram, it should be checked by a designated person to ensure there are no errors (including the distance between the leads and the ground, as well as the safety distance, etc.) before applying pressure.
(6) “For pressurized lead, check if the pressure regulator is at zero position. Only when it is at zero can the pressure be applied. And the operation can only be carried out after loudly shouting ‘Increase pressure!’”
(7) During the voltage increase process, the changes in the voltmeter and other meters should be monitored. When the voltage reaches 0.5 times the rated test voltage, the capacitive current of the tested equipment should be read. When the voltage reaches the rated voltage, the time should be started to be calculated. After the time is up, the voltage should be slowly reduced.
(8) Voltage rise rate: It can be slightly faster below 1/3 of the test voltage. After that, the voltage rise should be uniform, approximately at a rate of 3% of the test voltage per second, or it should be raised to the rated test voltage within 10 to 15 seconds.
(9) If during the test, the pointer of the meter swings, or if the test sample or the test instrument emits abnormal sounds, smoke, or flames, the voltage should be immediately reduced. After hanging a grounding wire on the high-voltage side, the cause should be investigated.
(10) If there are no specific requirements for the test sample, the general test duration is 1 minute. For insulating rods and other tools, the test duration is 5 minutes. After the test, a grounding wire should be hung and then the relevant parts should be touched to ensure there is no heating.
(11) The test voltage value must be accurately determined. Especially for the withstand voltage test of the generator, strict supervision is necessary to ensure that it does not exceed the specified value.
(12) Before and after the test, the insulation resistance and absorption ratio of the tested equipment should be measured. The results of the two measurements should not show any significant differences.
Post time: Apr-07-2026