DC breakdown voltage and the difference between the measured insulation resistance, AC withstand voltage test

The principle of measuring the DC leakage current of the insulator and measuring the insulation resistance is basically the same. The difference is that the voltage of the DC high voltage generator leakage test is generally higher than that of the insulation resistance tester, and it can be arbitrarily adjusted. The insulation resistance tester is not. Therefore, it is more effective than the insulation resistance tester to find defects, and it can be sensitive. It reflects the cracks of porcelain insulation, the internal moisture of the interlayer insulation and the local loose fracture, the deterioration of the insulating oil, the carbonization of the insulation along the surface, and so on.

Although the methods of measuring the withstand voltage and leakage current of DC high-voltage generators are inconsistent, their effects are different. The former is to test the insulation strength of the insulation, and the latter is used to check the insulation status, and the test voltage is relatively low. Therefore, the DC withstand voltage has special significance for the detection of some local defects. It is widely used in the preventive tests of high-voltage motors, cables, and capacitors. At the same time, it has the following characteristics compared with AC withstand voltage test:

1, the test equipment is light and small, if the cable line, if you do the AC voltage withstand test, the capacitor current per kilometer will reach several amps, the need for larger capacity test equipment. When DC high voltage generator is used for DC withstand voltage test, it only needs to supply insulation leakage current (up to only milliampere level) after stabilization.

2. The leakage current can be measured at the same time. The DC high-voltage generator DC withstanding voltage test increases the pressure step by step, and measures the leakage current to more effectively reflect the concentration defect inside the insulation.

3. Less damage to insulation, DC high voltage generator has less damage to the insulation of the test object. When the DC voltage is high enough to cause partial discharge in the air gap, the reverse electric field induced by the load generated by the discharge will make The field strength in the air gap weakens, thereby suppressing the partial discharge process in the air gap. If a high-voltage test transformer is used for the AC voltage withstand test, since the voltage is constantly changing direction, partial discharges will occur in each half-wave after the discharge occurs in the air gap. Such discharges often promote the decomposition and aging of organic insulating materials. Deterioration, reducing its insulation properties, so that the gradual increase of local defects.

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