The development of high voltage motor is closely related to the development of insulation data, insulation structure and insulation technology. As early as 1910, the first use of shellac mica foil rolling set of tube insulation. 1919 began to develop asphalt mica belt continuous insulation, and through the vacuum immersion treatment. The insulation mode of shenyang high-voltage motor is superior to the casing type and has higher electrical and mechanical properties. However, due to the inherent defect of asphalt thermoplasticity, it cannot meet the increasing demand of motor capacity and voltage. In the forties, the continuous insulation of mica strips impregnated with unsaturated polyester was studied, and in 1949 it was successfully used in large turbo-generators.

Compared with asphalt, thermosetting synthetic resin insulation, electrical, mechanical and heat resistance properties are significantly improved, and the corresponding mica tape reinforcement data are also changed from natural fiber to organic synthetic fiber or glass fiber fabric. At this point, the insulation heat resistance grade of high voltage motor from A to B. With the development and application of powdery mica, the research of solderless low viscosity synthetic resin and the new development of insulation structure of high voltage motor are promoted. Since 1952, modified epoxy resin has been used as adhesive powder mica tape. Its thermal physical properties, electrical and mechanical properties indicate that epoxy resin is superior to polyester resin. At present, it is preferred to use heat-resistant epoxy instead of ordinary epoxy. Some modified epoxy has reached grade F abroad, but it is still used as grade B in large motors.

Insulation structure and disposal process of high voltage motors in various countries can be roughly summarized as the following:

(1) multi-adhesive mica belt is continuously wrapped, dry in vacuum, and then hot-pressed (molded or hydraulic).

(2) multi-adhesive mica belt is continuously wrapped, without boring vacuum, directly using hot molding.

(3) mica with little glue is continuously wrapped, soaked in solvent-free resin in vacuum, and then hot-pressed.

(4) mica tape with little glue (or white blank tape) is continuously wrapped, i.e., the line is scattered, and then the solvent free resin impregnation is stopped.

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