In the operation of power equipment, the insulation will gradually deteriorate under the action of electric field, temperature and mechanical vibration for a long time, including overall deterioration and partial deterioration, forming defects. The AC withstand voltage test is a direct and effective method to identify the insulation strength of power equipment, and is an important part of the preventive test. In addition, because the AC withstand voltage test voltage is generally higher than the operating voltage, after passing the test, the equipment has a larger safety margin, so the AC withstand voltage test is an important means to ensure the safe operation of power equipment. The abnormal problems in the AC withstand voltage test are as follows:

1. If power is applied to the voltage regulator, the voltmeter will indicate that the voltage regulator is not at the zero position. If the ammeter also shows abnormal readings at this time, there may be a short circuit on the output side of the voltage regulator.

2. Adjust the voltage regulator, the voltmeter has no indication, it may be the carbon brush contact is not good, or the primary winding of the transformer, the measuring winding has broken wires.

3. During the test, the indication of the ammeter rises or drops suddenly, and the indication of the voltmeter drops suddenly, which is a symbol of the breakdown of the tested product.

4. In the step-up or withstand voltage stage, if the discharge sound is "squeak-", "squeak-squeak", or a very dull sound, the indication of the ammeter immediately exceeds the z large deflection indication, which is often caused by the creepage of the solid insulation of. If it is a noise like fried beans, the ammeter indication is very stable, this may be the discharge of suspended metal parts to the ground.

5. If due to the influence of air humidity or dirt on the surface of the tested product, the surface gliding discharge should not be regarded as unqualified. The surface should be cleaned and treated before testing to determine whether it is qualified. If the insulation of the porcelain glaze layer on the surface of the test product is damaged, aged or has cracks, it shall be regarded as unqualified.