Commonly used insulating materials for electricians can be divided into inorganic insulating materials, organic insulating materials and mixed insulating materials according to their different chemical properties. Commonly used inorganic insulating materials are: mica, asbestos, marble, porcelain, glass, sulfur yellow, etc., mainly used as motors, electrical winding insulation, switch base plate and insulators. Organic insulating materials are: shellac, resin, rubber, cotton, paper, hemp, rayon, etc., mostly used to manufacture insulating paint, winding wire covered insulator. Mixed insulating materials from the above two materials are processed into a variety of molded insulating materials, used as the base of electrical appliances, shells and so on.
The role of the insulating material is to separate the charged parts with different potentials in the electrical equipment. Therefore, the first insulating material should have high insulation resistance and voltage strength, and can avoid leakage, breakdown and other accidents. Secondly, heat resistance should be good, to avoid aging and deterioration due to long-term overheating; in addition, there should also be good thermal conductivity, moisture resistance and lightning resistance and high mechanical strength, as well as easy processing and other characteristics. According to the above requirements, the performance index of commonly used insulating materials are insulation strength, tensile strength, specific gravity, coefficient of expansion and so on.
Insulation strength: the higher the voltage applied to both ends of the insulator, the greater the electric field force on the charge within the material, the easier it is to ionize the collision, resulting in breakdown of the insulator. Make the insulator breakdown of the lowest voltage is called the breakdown voltage of the insulator. Make 1 millimeter thick insulating material breakdown, need to add the voltage kilovolts called insulating material insulation withstand voltage strength, referred to as insulation strength. As insulating materials have a certain insulation strength, a variety of electrical equipment, a variety of safety equipment (electrician's pliers, electric pen, insulating gloves, insulating rods, etc.), a variety of electrical materials, manufacturers have stipulated a certain permissible use of voltage, known as the rated voltage. The use of the voltage shall not exceed its rated voltage value, in order to avoid accidents.
Tensile strength: insulating material unit cross-sectional area can withstand the tensile force, such as glass per square centimeter cross-sectional area can withstand 1400 Newton's tensile force.
Insulating material insulation performance and temperature has a close relationship. The higher the temperature, the worse the insulating properties of the insulating material. In order to ensure the insulating strength, each insulating material has an appropriate maximum allowable working temperature, in this temperature below, can be used safely for a long time, more than this temperature will be rapidly aging. According to the degree of heat resistance, the insulation material is divided into Y, A, E, B, F, H, C and other levels. For example, the maximum permissible working temperature of class A insulating materials is 105℃, and most of the insulating materials in the distribution transformers and motors in general use belong to class A.
Thermal class Maximum allowable working temperature (℃) Brief description of insulating materials equivalent to this thermal class
Y90 Insulating structures made of unimpregnated cotton, silk, paper, etc. or combinations thereof.
A105 Insulating structures made of impregnated or immersed in liquid dielectrics (e.g. transformer oil in cotton yarn, silk and paper or combinations thereof)
E120 Insulating structures consisting of synthetic organic films, synthetic organic enamels and other materials or combinations thereof
B130 Insulating structures consisting of mica, glass fibers, asbestos, etc., and other inorganic materials, suitable organic materials or combinations thereof, bonded or impregnated with suitable resins or coated therewith.
F155 Insulating structures consisting of mica, glass fiber, asbestos, etc., bonded or impregnated or coated with suitable resins, as well as other inorganic materials, suitable organic materials or combinations thereof.
H180 Insulating structures consisting of mica, glass fiber, asbestos, etc., or combinations thereof, bonded or impregnated or coated with suitable resins (e.g. silicone resins).
C180 Insulating structures consisting of mica, glass fibers, unimpregnated mica, ceramics, quartz, etc., or combinations thereof, bonded or impregnated with suitable resins, coated or impregnated.
