Why do AC withstand voltage tests on power equipment?

The AC withstand voltage test is the most effective and direct method to identify the insulation strength of power equipment.

In the operation of power equipment, the insulation will gradually deteriorate due to the effects of electric field, temperature and mechanical vibration for a long time. Including overall degradation and partial degradation, forming defects. For example, because the electric field is concentrated in some places or the local insulation is weak, there are local defects. Various preventive test methods, each with its own strengths, can find some defects and reflect the insulation status, but the test voltage of other test methods is often lower than the working voltage of electric equipment, which is not strong enough as a guarantee for safe operation . Although the DC withstand voltage test is relatively high, some insulation weaknesses can be found, but because the insulation of power equipment is mostly a composite dielectric, under the action of DC voltage, its voltage is distributed according to resistance, so AC power equipment is Weaknesses under AC electric field may not be found by using DC as a test. For example, the defects of the generator groove are not easy to be found under DC. The AC withstand voltage test conforms to the electrical conditions that the power equipment is subjected to during operation. At the same time, the AC withstand voltage test voltage is generally higher than the operating voltage. Therefore, after the test, the equipment has a larger safety margin, so this test has become a guarantee of safety An important means of operation.

However, because the test voltage used in the AC withstand voltage test is much higher than the operating voltage, an excessively high voltage will increase the loss of the insulating medium, heat, and discharge, and will accelerate the development of insulation defects. Therefore, in a sense, The AC withstand voltage test is a destructive test.

Before the AC withstand voltage test, various non-destructive tests must be carried out in advance, such as measuring insulation resistance, absorption ratio, dielectric loss factor tg￠, DC leakage current, etc., and comprehensively analyzing the test results to determine the equipment Whether it is damp or contains defects. If an existing problem is found, it needs to be dealt with in advance. After the defect is eliminated, the AC withstand voltage test can be carried out, so as to avoid insulation breakdown during the AC withstand voltage test, expand insulation defects, extend the maintenance time, and increase the maintenance workload .