The insulating materials used in power and distribution transformers must possess the following properties:
- Good electrical properties to withstand the power frequency (50 Hz) voltages and impulse overvoltages.
- Good mechanical properties to withstand fabrication and handling during manufacture and electromagnetic forces during overload, short circuit, and normal operating conditions.
- 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|