Insulating Materials for Power & Distribution Transformers

The insulating materials used in power and distribution transformers must possess the following properties:

  1. Good electrical properties to withstand the power frequency (50 Hz) voltages and impulse overvoltages.
  2. Good mechanical properties to withstand fabrication and handling during manufacture and electromagnetic forces during overload, short circuit, and normal operating conditions.
  3. Good thermal stability and low ageing effect.

The insulating materials for different parts are indicated below.

Low voltage coil to ground and high voltage coil to low voltage coil Thick radial spacers or tubes made up of pressboard, paper, glass fabric, paper filled plastic laminates, or porcelain
Turn to Turn Organic enamel, papers, glass tapes
Layer to Layer, Coil to Coil Kraft paper, glass fabric, press board, varnished paper.
Fluid (used as insulating and cooling medium) Mineral oil, air, nitrogen
Bushings Porcelain, phenolic bonded tubes

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