The main function of insulators is to achieve electrical insulation and mechanical fixation, for which various electrical and mechanical performance requirements are specified. For example, under the specified operating voltage, lightning overvoltage, and internal overvoltage, there should be no breakdown or surface flashover; under the specified long-term and short-term mechanical loads, there should be no damage or destruction; after long-term operation under specified mechanical, electrical loads and various environmental conditions, there should be no significant deterioration; the metal fittings of the insulator should not produce any noticeable corona discharge under the operating voltage to avoid interference with radio or television reception. As insulators are widely used, their connecting metal fittings are also required to be interchangeable. Furthermore, technical standards for insulators stipulate various electrical, mechanical, physical, and environmental condition tests according to the model and usage conditions to verify their performance and quality.