(1) The effect of temperature, the temperature on the insulation resistance is large, the insulation resistance decreases as the temperature rises. The reason is that temperature, dielectric polarization increased conductance increase the insulation resistance decreases due to changes in temperature and the degree of change in the nature of the insulating material, structure and so on.

(2) Effect humidity and humidity on the surface leakage current is large, because the insulating surface adsorbed moisture, water film, the insulation resistance will significantly decrease.

(3) insulator mechanical overload caused by deterioration.

(4) porcelain pieces hygroscopic deteriorated.

(5) The internal and external stress porcelain pieces overlap deteriorated.

(6) Insulators deterioration caused by thermal expansion.

(7) steel cap pouring cement loaded with saturated expansive deteriorated.

(8) steel cap installed cement poured freezing expansion deteriorated.

(9) steel cap, steel pin electrical corrosion degradation.

(10) caused by the deterioration of the insulator overvoltage.

(11) internal defects caused by the deterioration of the insulator.