The direct factor that causes the partial discharge phenomenon of power transformers is nothing more than the uneven electric field strength. As long as we monitor the following two points in place during the manufacturing process of the transformer, it can greatly reduce the partial discharge defects of the transformer:

(1) Asymmetry of equipment electrode

If it is a needle or cylinder, such as the bushing outlet terminal of the transformer or the connection of the inner bushing conductor of the transformer, if the contact is not good, the electric field will be concentrated in these parts. If effective measures are not taken or the manufacturing quality is poor , It is easy to cause tip or surface discharge.

(2) Uneven insulation

In the internal manufacturing process of the transformer, in addition to insulating oil, various solid media, such as resins, plastics, mica, and fiber products, are used. Since the dielectric constant of the gas is not large, less than the relative dielectric constant of various liquids and solids, when there are bubbles in the oil or there are voids in the solid insulating material during the manufacturing process, the bubbles or the gas in the void are intersecting. The field experienced in the variable field is strong, but the withstand voltage is low, which is only a fraction or tenth of the solid medium and liquid medium, so discharge is first caused in these air gaps. Generally, if the oil is handled improperly, there will be bubbles in the oil, or the aging of the insulating material during the operation of the transformer will also cause bubbles. The bubbles greatly reduce the initial voltage generated by the partial discharge. Cause partial discharge, and if the oil contains impurities or high water content, it will also triple the maximum electric field strength in the oil, leading to discharge when the test voltage is low.