Electrical Performance A destructive discharge along the insulation surface is called flashover, and flashover characteristics are a key electrical performance characteristic of insulators. For different voltage levels, the withstand voltage requirements for insulators vary, and these requirements include power frequency dry and wet withstand voltage, lightning impulse withstand voltage, lightning impulse cut-off withstand voltage, and switching impulse withstand voltage. To avoid breakdown during operation, the breakdown voltage of an insulator is higher than its flashover voltage. In factory testing, breakable porcelain insulators generally undergo a spark test, where high voltage is applied to generate frequent sparks on the insulation surface for a certain period to see if breakdown occurs. Some insulators also require corona testing, radio interference testing, partial discharge testing, and dielectric loss testing. Insulators in high-altitude areas experience a decrease in electrical strength due to reduced air density; therefore, their withstand voltage should be increased accordingly when converted to standard atmospheric conditions. The flashover voltage of a polluted insulator when damp is significantly lower than its dry and wet flashover voltages. Therefore, in polluted areas, insulation must be reinforced or pollution-resistant insulators must be used, with a higher creepage distance (the ratio of creepage distance to rated voltage) than normal types. Compared to AC insulators, DC insulators have a poorer electric field distribution and exhibit particle adsorption and electrolysis effects, resulting in a lower flashover voltage. They generally require special structural designs and larger creepage distances.
Mechanical Properties: Insulators are frequently subjected to the weight and tension of conductors, wind force, icing weight, insulator self-weight, conductor vibration, mechanical forces from equipment operation, short-circuit electrodynamic forces, earthquakes, and other mechanical forces during operation. Relevant standards have strict requirements for mechanical properties.
Thermal Properties: Outdoor insulators must be able to withstand rapid temperature changes. For example, porcelain insulators must withstand several thermal cycles without cracking. Because current flows through insulating bushings, the temperature rise of their components and insulation parts, as well as the permissible short-time current value, must comply with relevant standards.
