The primary function of insulators is to achieve electrical insulation and mechanical fixation, for which various electrical and mechanical performance requirements are specified. For instance, under the action of specified operating voltages, lightning overvoltages, and internal overvoltages, no breakdown or surface flashover should occur; under the action of specified long-term and short-term mechanical loads, no damage or destruction should take place; after long-term operation under specified mechanical, electrical loads and various environmental conditions, no significant deterioration should occur; the metal fittings of insulators should not produce noticeable corona discharge under operating voltages to avoid interference with radio or television reception. Since insulators are widely used, their connecting fittings are also required to be interchangeable. Furthermore, the technical standards for insulators demand various electrical, mechanical, physical, and environmental condition tests, depending on the model and usage conditions, to verify their performance and quality.