Insulating materials are also called dielectrics. Contrary to the conductive material, it is actually non-conductive under the applied DC voltage, except for very small so-called leakage current.
The main functions of insulation materials of heat shrinkable tubes in various electrical machines, appliances, switches, wires, cables and radio devices are as follows:
First, insulate the conductor from other parts.
Secondly, it separates conductors of different potentials.
Thirdly, it is used to improve the potential gradient in high voltage electric field.
Fourth, it guarantees capacitors and other electrical appliances to achieve the required capacitance.
In the structure of electrical products, double-wall heat shrinkable sleeve is often used, and insulation material plays an extremely important role. This is because:
(1) In modern electricians, more and more high-voltage power transmission and large-capacity motors and electrical appliances are widely used. At the same time, the use of electrical equipment in tropical, cold, plateau, ocean, high altitude, underground and other places is expanding.
(2) The emergence of atomic power plants, high-frequency and ultra-high-frequency radio transmitters and receivers, as well as radio locators and television agencies.
Therefore, it is possible to further improve the accuracy and safety of its work only when new insulating materials are used. You can learn about the identification of heat shrinkable casing.
There are two kinds of practical insulating materials in electrical engineering, natural and artificial, according to their sources. The former includes cotton yarn, cloth, natural resin, natural rubber, vegetable oil and petroleum products; the latter includes glass fiber, synthetic fiber, synthetic film and resin. According to its morphology, it can be divided into four categories: gas, liquid, elastomer and solid. Among the commonly used insulating materials, the solid type is the most. According to its chemical molecular structure, there are two kinds: organic and inorganic. The former contains carbon element C in its chemical molecular structure, while the latter does not contain carbon element.
The main performance requirements for different types of motors and electrical appliances are as follows:
1. High Voltage Motor
In high voltage motors, the electrical breakdown strength of insulating materials should be high and the dielectric loss should be small. In addition, because of the electromagnetic and mechanical vibration during the operation of the high voltage motor, the insulation system is required to have good stiffness, integrity and thermoelasticity; the dielectric coefficients of different insulating materials in the insulation structure should be close or equal, so that the voltage distribution on the insulator does not differ greatly, and has the ability to resist atmospheric overvoltage and internal overvoltage.
The new type of high-voltage and large-capacity generator and motor (whose insulation is B or F grade) can meet the above requirements better when using powder mica, bisphenol A epoxy resin or aliphatic epoxy resin (or linear phenolic epoxy resin) as insulation, plus appropriate corona-proof treatment and insulation technology (for windings).
2. Low Voltage Motor and Electrical Appliances for Electric Power
In general low-voltage motors and electrical appliances, there are fewer problems caused directly by dielectric properties of insulating materials, but there are many accidents such as turn-to-turn and inter-phase short circuit, breakdown of ground insulation and so on, due to insufficient mechanical strength and temperature rise. Therefore, insulating materials are required to withstand various forms of mechanical loads and to be durable.
3. DC Motor and Electrical Appliances
In general DC motors and electrical appliances, the insulation system works well because its current direction and size remain unchanged. However, in high temperature or high speed motors used in metallurgical, coal mine, ship and traction systems, in order to solve the problems of high heating, severe humidification, severe vibration or bearing centrifugal force in insulating parts, composite insulating materials such as silicone resin, polyimide and aromatic polyftamine should be used.