In transformer construction it is obviously very important that the insulation be of the best quality to prevent burn outs and interruptions of service.
Ques. What is the "major" insulation?
Ans. The insulation placed between the core and secondary (low pressure) coils, and between the primary and secondary coils.
Fig. 1,973.—Assembled coils of General Electric water cooled 500 kva., 66,000 volt transformer.
It consists usually of mica tubes, sometimes applied as sheets held in place by the windings, when no ventilating ducts are provided, or moulded to correct form and held between sheets of tough insulating material where ducts are provided for air or oil circulation.
Ques. Describe the "minor" insulation.
Ans. It is the insulation placed between adjacent turns of the coils.
Since the difference of pressure is small between the adjacent turns the insulation need not be very thick. It usually consists of a double thickness of cotton wrapped around each conductor. For round conductors, the ordinary double covered magnet wire is satisfactory.
Ques. What is the most efficient insulating material for transformers?