Insulation Materials used in Transformers and 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 90oC
  • Some of the materials used are cotton, silk, paper, wood without impregnated

Class A:

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

Class E:

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

Class B:

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

Class F:

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

Class H:

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

Class C:

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