Mechanical properties of high voltage insulator
The basic performance of high voltage insulator includes electrical, mechanical and thermal performance. Also, it has environmental and ageing resistance properties.
① electrical performance: the destructive discharge along the insulation surface is called flashover, which is the main electrical performance of high-voltage insulator. For different voltage levels, the basic performance includes electrical, mechanical and thermal performance. Besides, it has environmental and ageing resistance properties.
The withstand voltage requirements of are different, and the indicators include power frequency dry and wet withstand voltage, lightning impulse withstand voltage, lightning impulse cut-off withstand voltage, operation impulse withstand voltage, etc. To avoid a breakdown in operation, the breakdown voltage of high-voltage insulator is higher than the flashover voltage. In the factory test, the porcelain insulator which can be broken down generally goes through the spark test, that is to say, frequent sparks occur on the surface of the high-voltage insulator for a certain period to see whether it is broken down. Its basic properties include electrical, mechanical and thermal properties. Also, it has environmental and ageing resistance properties.
Corona test, radio interference test, partial discharge test and dielectric loss test are also required. In high altitude area, the electrical strength of insulator decreases due to the decrease of air density, so its withstand voltage should be increased when converted to standard atmospheric conditions. The flashover voltage of polluted high-voltage insulator when it is damp is much lower than its dry and wet flashover voltage. Therefore, in a polluted area, it is necessary to strengthen insulation or adopt pollution resistant insulator, and its creepage distance (ratio of creepage distance to rated voltage) should be higher than that of the normal type. Compared with AC high-voltage insulator, DC insulator has poor electric field distribution, adsorption of pollution particles and electrolysis, low flashover voltage, and generally requires special structure design and larger creepage distance.
② mechanical performance of high-voltage insulator: the model of the high-voltage insulator is often affected by the gravity and tension of conductor, wind force, icing weight, self-weight of an insulator, the vibration of the conductor, the mechanical force of equipment operation, short-circuit electric force, earthquake and other mechanical forces. Relevant standards have strict requirements for mechanical properties.
③ thermal performance of high-voltage insulator: outdoor high-voltage insulator is required to be able to withstand sudden temperature change. For example, porcelain insulator is required to pass several cold and hot cycles without cracking. Due to the current passing through the insulating sleeve, the temperature rise and allowable short-time current value of its parts and insulating parts shall meet the requirements of relevant standards.
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