Insulation Materials Used in Transformers & Induction Motors

Insulation materials used in transformers and motors are classified based on the temperature withstand capability.

Some of the insulation classes used in transformers and induction motors are: Class Y, Class A, Class E, Class B, Class F, Class H and Class C.

Class Y

  • Maximum hot spot temperature for this type of insulator is 90°C.
  • Some of the materials used are cotton, silk, paper, wood without impregnated.

Class A

  • Maximum hot spot temperature for this type of insulator is 105°C.
  • Cotton, Silk, and Paper when suitably impregnated are the type of materials used.

Class E

  • Hot spot temperature is 120°C.
  • Materials possessing degree of thermal stability allowing them to be operated at a temperature 15°C above higher than Class A. Ex: wire, enamel etc

Class B

  • Maximum hotspot temperature is 130°C.
  • Mica, Glass fibre, asbestos, etc with suitable impregnation or coating substance.

Class F

  • Hot spot temperature is 155°C.
  • Mica, glass, asbestos etc with suitable binding impregnation or coating substances capable of withstanding 25°C higher than Class B.

Class H

  • Maximum hotspot temperature of 180°C.
  • Combination of materials such as mica, glass fibre, asbestos suitably bonded.

Class C

  • Hotspot temperature above 180°C.
  • Mica, porcelain, glass, quartz, and asbestos with and without inorganic binder.

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