Insulation materials commonly used by electricians are classified into inorganic insulating materials, organic insulating materials and mixed insulating materials according to their chemical properties. Commonly used inorganic insulating materials are: mica, asbestos, marble, porcelain, glass, sulfur, etc., mainly used as winding insulation for motors and electrical appliances, bottom plates and insulators for switches. Organic insulating materials are: shellac, resin, rubber, cotton yarn, paper, hemp, rayon, etc., mostly used to make insulating varnish, coated insulation of winding wires, etc. The hybrid insulating material is a variety of molded insulating materials which are processed by the above two materials, and are used as a base, an outer casing, and the like of an electric appliance.

The function of the insulating material is to isolate the charged parts of different electrical potentials in the electrical equipment. Therefore, the insulating material should first have high insulation resistance and compressive strength, and can avoid accidents such as electric leakage and breakdown. Secondly, the heat resistance is better, avoiding deterioration due to long-term overheating; in addition, it should have good thermal conductivity, moisture resistance, high mechanical strength and convenient processing. According to the above requirements, the performance indexes of commonly used insulating materials include dielectric strength, tensile strength, specific gravity, and expansion coefficient.

Insulation withstand voltage: The higher the voltage applied across the insulator, the greater the electric field force received by the charge in the material, and the more likely the ionization collision occurs, causing breakdown of the insulator. The lowest voltage at which an insulator breaks down is called the breakdown voltage of this insulator. When a 1 mm thick insulating material is broken down, the voltage kilovolts to be applied is called the dielectric withstand strength of the insulating material, which is referred to as the dielectric strength. Because the insulating materials have certain insulation strength, various electrical equipment, various safety appliances (electrician pliers, electroscope, insulating gloves, insulating rods, etc.), various electrical materials, manufacturers have specified a certain allowable voltage, called It is rated voltage. The voltage to be used during use shall not exceed its rated voltage to avoid accidents.

Tensile strength: The tensile force that can be withstood by the cross-sectional area of the insulating material. For example, the cross-sectional area per square centigdkker of glass can withstand a tensile force of 1400 Newtons.

The insulation properties of insulating materials are closely related to temperature. The higher the temperature, the worse the insulation properties of the insulating material. To ensure dielectric strength, each insulating material has an appropriate maximum allowable operating temperature below which temperatures can be safely used for long periods of time. Above this temperature, it will age rapidly. According to the degree of heat resistance, the insulating materials are classified into Y, A, E, B, F, H, C and the like. For example, the maximum allowable operating temperature of Class A insulation materials is 105 °C. Most of the insulation materials used in distribution transformers and motors are Class A.

Heat resistance rating maximum allowable operating temperature (°C) equivalent to the heat-resistant grade of insulating material

Y90 is an insulating structure composed of unimpregnated cotton yarn, silk and paper or the like or a combination thereof

A105 is an insulating structure consisting of impregnated or immersed in a liquid dielectric (such as cotton yarn, silk and paper in transformer oil or a combination thereof)

E120 is an insulating structure composed of a composition of a synthetic organic film, a synthetic organic enamel, or the like.

B130 is an insulating structure composed of a suitable resin bonded or impregnated, coated mica, glass fiber, asbestos, etc., and other inorganic materials, suitable organic materials or combinations thereof.

F155 is an insulating structure composed of a suitable resin bonded or impregnated, coated mica, glass fiber, asbestos, etc., and other inorganic materials, suitable organic materials or combinations thereof.

H180 is an insulating structure composed of a suitable resin (such as silicone resin) bonded or impregnated, coated mica, glass fiber, asbestos, or the like or a combination thereof.

An insulating structure composed of a material of C180 or more bonded or impregnated with a suitable resin, coated mica, glass fiber, and unimpregnated mica, ceramic, quartz, or the like, or a combination thereof