The power frequency AC withstand voltage test is to apply a certain voltage to the tested product and keep it for a certain period of time to consider the ability of the tested product's insulation to withstand various voltages, so as to ensure the safe operation of the equipment. Although many insulation defects can be found in insulation resistance and absorption ratio test, leakage current and DC withstand voltage test, and dielectric loss angle measurement test, etc., because the test voltage is lower than the working voltage of the tested product, it is often not timely for some insulation defects It was found that in order to further expose equipment defects, check the insulation level of electrical equipment and ensure that it can be put into operation, it is necessary to conduct an AC withstand voltage test.

It is the most effective and direct method to determine the insulation strength of electrical equipment, and it is of decisive significance for judging whether electrical equipment can be put into operation. The voltage, waveform, frequency of the AC withstand voltage test and the distribution of the internal voltage of the insulation of the tested product are in line with the actual operating conditions. Therefore, the AC withstand voltage can effectively find the more dangerous concentrated defects in the electrical equipment.

 The higher the test voltage, the higher the effectiveness of finding insulation defects, but the greater the possibility of the test product being broken down. For a sample with good insulation, the AC withstand voltage will gradually weaken the insulation strength, forming an accumulation effect of poor quality inside the insulation. The value of the insulation breakdown voltage is not only related to the applied voltage, but also related to the duration of the application. The breakdown voltage gradually decreases with the increase of the application time. Therefore, it is necessary to correctly select the test voltage standard and withstand voltage time and equipment-test transformer.