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Friday, 9 August 2019

General Properties of Insulating Materials


Insulating materials are those which offer very high resistance to the flow of electric current. They require extremely high voltage of the order of kilovolt or megavolt to send a few milli-amperes of current through them. They are non-metallic materials and are used to prevent leakage of current from one conductor to another or to earth. Almost all insulating materials have negative temperature co-efficient of resistance and as such their resistivity is reduced with increase in temperature. The function of any insulator is very important, for without which no electrical machines can work. Ideal insulators are those substances into which static electric field penetrate uniformly. Primarily they are used for storage of electrostatic energy as in capacitor which are known as dielectrics. But in this blog we will be dealing only with that part of its function which will prevent flow of electric current to any undesired conducting medium. The insulators provide mechanical strength as well as insulation to the conductors. Wood, Paper, Mica, Oil, Plastics, Asbestos, Porcelain, are some of the examples of insulating materials.

Some important applications of insulators in the field of electrical engineering are:

(a) To isolate the overhead conductors from earth in the transmission and distribution of electrical energy.
(b) In all rotary machines to isolate the winding from the body and other unwanted current path.
(c) In transformers to isolate the winding from the core or magnetic path.
(d) In industrial and house wiring to isolate the conductor earthing.
(e) In all domestic, commercial electrical equipments to isolate the conductor from earth or body.

General Properties of Insulating Materials:

Majority of the breakdown in the field of electrical engineering is due to the failure of insulation. The importance of insulating material is ever increasing day by day and there are innumerable number of types of insulations are available in the market. The selection of the right type of insulating materials for a particular job is very important because the life of the equipment will depend on the type of insulating material used. All insulators when used should not only behave as insulators over a wide range of electrical voltage but also should be strong enough mechanically, should not get affected by heat, atmosphere, chemical and should be free from deformation due to ageing. Therefore, the properties to be studies while selecting an insulator for a particular job are :

(c) Visual properties

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