Preventive tests of electrical equipment can be carried out through the following aspects.

1. Measure insulation resistance

It is the most common and simplest test method, usually measured with a megohmmeter. According to the measured insulation resistance of the test sample at 1 minute, it can be detected whether the insulation has continuous concentration defects, overall moisture or penetration moisture.

2. Measure leakage current

It is basically the same as the principle of measuring insulation resistance, and the nature of detected defects is also roughly the same. However, the power supply used in leakage current measurement is generally provided by high-voltage rectification equipment, and the leakage current is directly read by a micro-ampere meter. It has the characteristics that test voltage can be adjusted at will; high sensitivity and good measurement repeatability; conversion of insulation resistance value; insulation absorption ratio can be used to judge insulation defects.

3. Measuring the media loss angle

It is a test project with high sensitivity. It can find the local defects of the electrical equipment insulation as a whole being damp, degraded, deteriorated, and the small or small test equipment penetrated or not penetrated. But when the volume of the tested product is large, and the volume occupied by the defect is small, it is difficult to find by this method. It is widely used in electrician manufacturing and electrical equipment handover and preventive tests.

4. AC withstand voltage test

It is one of the destructive tests that can further diagnose the insulation defects of electrical equipment. The AC withstand voltage test is the most rigorous, effective, and direct test method for identifying the insulation strength of electrical equipment. It can detect the weakest point of insulation during normal operation and is decisive for determining whether electrical equipment can continue to be put into operation.

5. DC withstand voltage test

In addition to detecting dampness and deterioration of equipment insulation, it has a special role in finding some local defects in insulation. The DC withstand voltage test can find some defects that cannot be found by the AC withstand voltage test. The two tests, AC and DC withstand voltage test, cannot be replaced by each other. They must be used in preventive tests, especially motors, cables, etc. DC withstand voltage test.

6. Non-destructive test and destructive test

Non-destructive test: the test is performed at a lower voltage (lower than or close to the rated voltage). The test items such as measuring insulation resistance, leakage current and dielectric loss angle are non-destructive tests.

Destructive test: refers to the test carried out above the working voltage, also known as the withstand voltage test. During the test, a specified test voltage is applied to the insulation of the electrical equipment to test the withstand capability at this voltage. Both DC withstand voltage test and AC withstand voltage test are destructive tests

There is a certain order for these two types of tests. Non-destructive tests should be performed first, followed by destructive tests, so as to avoid undesirable breakdown accidents.