When the insulator is damaged, the glass fragments near the steel cap and iron foot are jammed, and the mechanical strength of the remaining part of the insulator is enough to prevent the insulator string from breaking. The material used to make glass insulators is more stable than the raw materials used in the manufacture of electric porcelain, which creates good conditions for the stability of the electrical and mechanical properties of the glass. Besides, because the mechanical strength of glass insulator surface is high, the surface is not easy to crack. The electrical strength of glass is generally unchanged during the whole operation period, and its aging process is much slower than that of porcelain.