Page 193 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

The tube containing the oil is heated rapidly with the help of an electric heater till the oil begins to boil. During the
process, oil should not produce cracking.
The other tests are:
• acidity test

• sludge resistance test.
Electrical insulating varnishes
They are of two types
Oil and resin varnishes.
Solid insulators/insulating materials

SI.No Classification Examples
1 Mineral insulators Mica, marble, slate.

2 Vitreous materials Glass, quartz, procelain.
3 Rubber and rubber products Rubber, vulcanised (India) rubber (V.I.R) ebonite
4 Waxes and compounds Paraffin wax, bitumen
5 Fibrous materials Asbestos, paper, wood, Press pahn, leatheroid,
cotton, silk, tapes etc.
6 Synthetic products Bakelite, shellac, oil (for Transformer Switchgear
etc).

Paper
Various grades of insulating paper are available for use in capacitors, cables, etc. Paper, if moist, loses its
insulating property. Therefore, it is used in an impregnated condition.
Wood
It is impregnated with oil or other substance for use as an insulator.
For example, in machine windings, bamboo wood is used as slot wedges.

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CITS : WCS - Electrical - Exercise 18