1 Electrical performance: Destructive discharge along the insulating surface is called flashover, and flashover characteristics are the main electrical properties of the insulator. For different voltage levels, the withstand voltage requirements of the insulators are different. The indicators include power frequency dry, wet withstand voltage, lightning impulse withstand voltage, lightning impulse cut-off withstand voltage, and operating impulse withstand voltage. In order to avoid breakdown during operation, the breakdown voltage of the insulator is higher than the flashover voltage. In the factory test, the puncturable porcelain insulator is generally subjected to a spark test, that is, a high voltage is applied to cause frequent sparking on the insulating surface for a certain period of time to see if it is broken down. Some insulators also need to undergo corona test, radio interference test, partial discharge test and dielectric loss test. In high-altitude insulators, the electrical strength decreases due to a decrease in air density. Therefore, the withstand voltage should be increased when converted to standard atmospheric conditions. The flashover voltage of a dirty insulator is much lower than that of its dry and wet flashover voltage. Therefore, the contaminated area must be reinforced or with a stain-resistant insulator. The creepage ratio (ratio of creepage to rated voltage) should be compared. Normal type is high. Compared with AC insulators, DC insulators have poor electric field distribution, adsorption of particles and electrolysis, and low flashover voltage. Generally, special structural design and larger creepage distance are required.
2 Mechanical properties: Insulators are often subjected to the gravity and tension of the wire, wind, ice weight, insulator weight, wire vibration, equipment operating mechanical force, short-circuit electric power, earthquake and other mechanical forces during operation. The relevant standards have strict requirements on mechanical performance regulations.
3 Thermal properties: Outdoor insulators are required to withstand rapid temperature changes. For example, porcelain insulators require several cycles of hot and cold without cracking. Due to the passage of current through the insulating sleeve, the temperature rise of its components and insulation and the allowable short-time current values shall comply with the relevant standards.
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