Insulation history

The earliest used insulating materials are cotton, silk, mica, rubber and other natural products. At the beginning of the 20th century, industrial synthetic plastic phenolic resin was first introduced, which has good electrical properties and high heat resistance. In the future, urea-formaldehyde resins and alkyd resins with better performance have appeared. The appearance of trichlorobiphenyl synthetic insulating oil has caused a leap in the specific characteristics of power capacitors (but has been discontinued due to harmful human health). Sulfur hexafluoride was also synthesized during the same period.

Synthetic insulation materials have been rapidly developed since the 1930s, mainly including acetal resin, neoprene, polyvinyl chloride, styrene butadiene rubber, polyamide, melamine, polyethylene, and PTFE, which is called plastic king. Wait. The emergence of these synthetic materials has played a major role in the development of electrical technology. For example, an acetal enameled wire is used for the motor, which increases the working temperature and reliability, and the size and weight of the motor are greatly reduced. The successful development of glass fiber and its woven tape and the synthesis of silicone resin have increased the heat resistance grade of Class H for motor insulation.

Unsaturated polyester and epoxy resin came out after the 1940s. The emergence of powder mica paper has freed people from the plight of the lack of mica resources.

Since the 1950s, synthetic resin-based new materials have been widely used, such as unsaturated polyester and epoxy insulation rubber for high-voltage motor coil impregnation. The polyester series products are used in motor slot lining insulation, enameled wire and impregnating varnish. The E-class and B-class low-voltage motor insulation has been developed to further reduce the volume and weight of the motor. Sulfur hexafluoride has been used in high-voltage electrical appliances and has been developed for large-capacity miniaturization. The air insulation of the circuit breaker and the oil and paper insulation of the transformer are partially replaced by sulfur hexafluoride.

In the 1960s, heat-resistant resins containing heterocyclic rings and aromatic rings have been greatly developed, such as polyimides, polyaramids, polyarylsulfones, polyphenylene sulfides, and the like, which are H-grade and higher heat-resistant grades. The synthesis of these heat-resistant materials has created favorable conditions for the development of Class F and Class H motors in the future. Polypropylene films have also been successfully used in power capacitors during this period.

Since the 1970s, the development of new materials has been relatively rare. This period is mainly to modify and expand the scope of existing materials. The mineral insulating oil is refined by a new method to reduce its loss; epoxy mica insulation has many improvements in improving its mechanical properties and achieving no air gap to improve its electrical properties. The power capacitor transitions from a paper-membrane composite structure to a full-film structure. The 1000 kV UHV power cable began to study the replacement of traditional natural fiber paper with synthetic paper insulation. Non-polluting insulation materials have also developed rapidly since the 1970s, such as the replacement of toxic medium chlorinated biphenyl with non-toxic medium isopropyl biphenyl and ester oil, and the expansion of solvent-free paint. With the popularization of household appliances, the fire of insulating materials has caused frequent fire accidents, so the research on flame retardant materials has attracted attention.

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