When the high-voltage test transformer gets damp, it mainly starts around its outer skin. The most important factor that causes the insulation of the high-voltage test transformer to be damp is the outer skin of the high-voltage test transformer. According to the electroosmosis phenomenon, the water molecules in the transformer are positively charged in the electric field. Form exists. However, once a positive voltage is applied to the transformer windings, the water molecules in the insulation will no longer be compatible, so the water molecules are discharged to flow to the shell, so that there are fewer water molecules inside, which will cause leakage inside the transformer. The current gradually decreases.

The principle of the opposite case is the same. If a negative voltage is applied to the transformer winding, the water molecules in the transformer will undergo the same change, which is mainly reflected in:

The water molecules in the insulation will be absorbed, and will move through the insulation towards the transformer winding. At this time, it will cause the moisture in the area with higher field strength in the insulation of the high-voltage test transformer to gradually increase, making the leakage current continue to increase.

At the same time, special attention should be paid to the voltage that the polarity cannot affect all high-voltage test transformers. The most representative situation here is the new high-voltage test transformer, and the voltage polarity cannot change the actual measurement data size of the new high-voltage test transformer.

Because the insulation of the high-voltage test transformer is generally not damp. The moisture in it can usually be in the range that is not considered. With the influence of the electric field, the electroosmosis will become insignificant. Therefore, the leakage current obtained during the positive and negative test voltages is basically the same. For those old transformers, the test voltage polarity will seriously affect the accuracy of the test measurement data.