Regarding the issue of using negative voltage to do the DC withstand voltage test on electrical equipment? To understand from two aspects:

1. In the DC high voltage test, the moisture and moisture contained in the insulation of the inspection equipment are the key to the insulation quality. Due to the electrodialysis phenomenon of moisture (that is, the water molecules have the property of positive ions in the electric field). During the test, the high voltage is applied to the live parts. Because the high voltage is of negative polarity, the water is easily adsorbed near the high voltage pole, which makes it easy to detect the object under test.

2. In an extremely uneven electric field, the breakdown voltage of the gas has a great relationship with the polarity of the charge on the electrode. In the same rod-to-board gap, the breakdown voltage when the rod is negatively charged is more than twice as high as when it is positively charged, that is, in an uneven electric field, the relationship between the discharge voltage of the rod-to-board gap and the polarity of the rod voltage : The discharge voltage is high when the bar is negative.

The external insulation of electrical equipment is close to this extremely uneven electric field. Generally, the external insulation level of electrical equipment is higher than the internal insulation, and the internal insulation and faults are also more than the external insulation. Do a DC withstand voltage test on the equipment. Although the internal and external insulation are tested, the main thing is to check the internal insulation. The internal insulation is mainly liquid. , Solid material, and adopts inter-electrode shielding measures, its positive and negative voltages have little effect on insulation breakdown. For example, the cable insulation is only 10% lower than the negative polarity in the positive polarity breakdown, and DC high voltage is applied to the equipment When testing the voltage, the external insulation is generally not expected to flashover. For this reason, a negative DC voltage is used.