History of the Development of Insulating Materials
The first insulating materials used are cotton, silk, mica, rubber and other natural products. In the early twentieth century, the industrial synthetic plastic phenolic resin was first introduced, and its electrical properties were good and the heat resistance was high. Later, a better performance of urea formaldehyde resin and alkyd resin have been developed. The appearance of three chlorinated biphenyl synthetic insulating oil has made a leap in the power capacitor’s bit character (but because it is harmful to human health, it has ceased to be used later). Six sulfur fluoride was also synthesized in the same period.
Since 30s, synthetic insulation materials have been developing rapidly, mainly including acetal resin, neoprene rubber, polyvinyl chloride, styrene butadiene rubber, polyamide, melamine, polyethylene and Teflon which is well known as the king of plastic. The appearance of these synthetic materials has played an important role in the development of electrical technology. For example, acetal enameled wire is used for motor to improve its working temperature and reliability, while the volume and weight of the motor are greatly reduced. The development of glass fiber and its braided belts and the synthesis of silicone resin have added the H grade to the insulation of the motor.
After 40s, unsaturated polyester and epoxy resin came out. The appearance of the powder mica paper makes people get rid of the plight of the lack of mica resources.
Since 50s, new materials based on synthetic resins have been widely used, such as unsaturated polyester and epoxy and other insulating adhesives for high voltage motor coil impregnation. The application of polyester products in motor slot lining, enameled wire and impregnating varnish has developed E and B grade low voltage motor insulation, so that the volume and weight of motor are further reduced. Six sulfur fluoride began to be used in high voltage electrical apparatus and made it to large capacity and miniaturization. The air insulation of the circuit breaker and the oil and paper insulation of the transformer are partially replaced by six sulphur fluoride.
In 60s, the heat resistant resins containing heterocyclic and aromatic rings have made great progress, such as polyimides, polyaromatics, polysulfone and polyphenylene sulfide, which belong to H grade and higher heat-resistant materials. The synthesis of these heat-resistant materials has created favorable conditions for the future development of F class and H grade motor. Polypropylene films have also been successfully used in power capacitors at this time.
Since 70s, the research on the development of new materials is relatively small. This period is mainly to make various modifications and expand the application scope of the existing materials. Refining the mineral oil by a new method to reduce its loss, epoxy mica insulation has made a lot of improvements in improving its mechanical properties and achieving no air gap in order to improve its electrical performance.
With the popularity of household appliances, the insulation material ignition and the major fire accidents have occurred frequently, so the research of flame retardant materials has aroused great attention.