Insulation Materials used in Transformers and Induction Motors

Electrical Engineering Electrical Machines
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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