Why do AC voltage withstand tests for power equipment?

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

During the operation of power equipment, insulation will gradually deteriorate due to the effects of electric field, temperature and mechanical vibration. Including the overall deterioration and partial deterioration, the formation of defects. For example, there are local defects due to local electric field concentration or partial insulation. All kinds of preventive test methods have their own merits. They can find some defects and reflect the status of insulation. However, the test voltages of other test methods are often lower than the working voltage of power equipment, and they are not strong enough for safe operation. . DC voltage test Although the test voltage is relatively high, some insulation weaknesses can be found, but most of the insulation of the power equipment is a combination of dielectrics. Under the effect of DC voltage, the voltage is distributed by resistance, so the AC power equipment is The weaknesses of AC electric fields are not always detectable by using dc test. For example, the defects of the generator's groove are not easily found under direct current. The AC withstand voltage test complies with the electrical conditions that the electrical 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 large safety margin, so this kind of test has become a safety guarantee. An important means of operation.

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

Before carrying out the AC voltage withstand test, various non-destructive tests must be performed in advance, such as measuring the insulation resistance, absorption ratio, dielectric loss factor tg¢, and DC leakage current, etc., and comprehensively analyze the test results to determine the equipment. Whether it is wet or contains defects. If it is found that there is a problem, it must be processed in advance. After the defect is eliminated, the AC withstand voltage test can be conducted to avoid insulation breakdown, expansion of insulation defects, extension of inspection time, and increase of inspection workload during AC withstand voltage test. .