What are the hazards of dirt and cracks on the surface of power fittings and transformer bushings?

Contamination on the surface of the casing is prone to flashover. When the line encounters lightning and becomes an operating overvoltage, it will cause flashover, which will cause tripping.

Cracks in the casing will reduce the electrical strength. Because of the crack, the crack will be filled with air, and the dielectric coefficient of the air is small, the dielectric coefficient of the porcelain bushing is large, and the electric field intensity distribution is related to the dielectric coefficient of the material. When the electric field strength in the crack reaches a certain value, the air will be freed, causing partial discharge or even breakdown. If moisture enters the crack, the casing can burst when it freezes.