How much do you know about solid insulation materials?
May 08, 2024
Solid insulating materials are solid materials used to isolate conductors of different potentials. Solid insulation materials are generally also required to have a supporting role. Compared with gas insulation materials and liquid insulation materials, solid insulation materials have a much higher breakdown strength due to their higher density, which is of great significance in reducing insulation thickness.
Overview Solid insulating materials are solid materials used to isolate conductors with different potentials. Generally, solid insulating materials are also required to have a supporting role.
Solid insulation materials can be divided into two categories: inorganic and organic.
Compared with gas insulation materials and liquid insulation materials, solid insulation materials have a much higher breakdown strength due to their higher density, which is of great significance for reducing insulation thickness. The insulation resistance, dielectric constant, and dielectric loss of solid insulating materials vary over a wide range.
For example, the insulation resistance of polytetrafluoroethylene can be as high as 1020Ω·m, which can prevent excessive leakage current, and its relative dielectric constant is very low (only 2.0), making the capacitance of the insulation very small; correspondingly, High-dielectric ceramics have extremely high relative dielectric constants (up to several thousand). Therefore, solid insulation materials can be selected according to different requirements.
Inorganic solids mainly include mica, powdered mica and mica products, glass, glass fiber, and their products, as well as electric porcelain, alumina film, etc. They are resistant to high temperatures, not easy to age, and have considerable mechanical strength. Some of them, such as electric porcelain, have low cost and occupy a certain position in applications. The disadvantage of inorganic solid insulation materials is that they have poor processing performance and are not easily adapted to the molding requirements of electrical equipment for insulation materials.
Mica and powdered mica products have long-term corona resistance and are an important component of the insulation structure of high-voltage equipment. They can also be used in high-temperature situations.
glass
The process of glass is simpler than that of ceramics and can be used to make insulators. Glass fiber can be made into silk, cloth, and tape. It has much higher heat resistance than organic fiber and plays an important role in the development of insulation structures at high temperatures.
Electric porcelain products have excellent discharge resistance and certain mechanical strength, so they are particularly suitable for high-voltage power transmission and distribution applications. After years of research, varieties with high mechanical strength, high-temperature resistance, and high dielectric constant have been developed.
In the 19th century, organic solids were mainly natural, such as paper, cotton, silk, rubber, and curable vegetable oils. These materials are flexible, can meet application process requirements, and are easy to obtain. Since the 20th century, the emergence of synthetic polymer materials has fundamentally changed the appearance of solid insulating materials.
Bakelite was first used as an insulating material. Later, polyethylene and polystyrene appeared. Due to their extremely small dielectric constant and dielectric loss, they met the requirements of high frequencies and adapted to the development of new technologies such as radar. Silicone resin combined with low-alkali glass cloth greatly improves the heat resistance level of motors and electrical appliances. Enameled wire made of polyvinyl formal as a paint base has opened up broad prospects for enameled wire, replacing silk-covered wire and yarn-covered wire. The thickness of polyester film is only a few tens of microns.
Using it to replace the original paper and cloth greatly improves the technical and economic indicators of motors and electrical appliances. The use of polyaramid fiber paper, polyester film, and polyimide film makes the heat resistance grades of motor slot insulation become F and H respectively (see insulation heat resistance grade and thermal aging test). There have been similar developments in elastomer materials, such as heat-resistant silicone rubber, oil-resistant nitrile rubber, and subsequently fluorine rubber, ethylene-propylene rubber, etc.
