(1) The installation and use of porcelain insulators is unreasonable. If the mechanical load exceeds the regulations, the voltage level does not meet the requirements, and the installation position is improper.
(2) Due to the sudden hot weather and the external damage of the hail.
(3) Flashover caused by thunderstorms and foggy weather due to contamination of porcelain insulators.
(4) Short circuit of electrical equipment, damage to porcelain insulator caused by excessive electric and mechanical stress.