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Wednesday, 14 August 2019

Chemical Properties of Insulating Materials

1. Chemical Properties: 


Insulating material do sometimes come in contact with chemicals. For example a pole insulator used in the transmission and distribution overhead lines comes in contact with the chemicals like nitrogen, hydrogen, in the atmosphere. When they come in contact with chemicals, the properties of the insulating materials to which it has been designed should not change.

2. Chemical Resistance: 

The insulating materials are chemically affected by the gases, water, acids, alkalies and salts. Chemically a material is a better insulating material if it resists chemical reaction. For example, plastic is mostly used in place of paper insulation in many applications because it is not affected by chemicals and is less hygroscopic. The chemical resistance requirements of insulating materials used in underground cables which are likely to operate under severe chemical condition due to water, salts, acids or alkalies, will be more demanding than those of the insulating materials used in motor winding.

3. Hygrucopicity: 

Many insulators come in contact with atmosphere either during manufacturers, operation or both. The contact of insulation with atmosphere is often so complete that even the less chemically aggressive atmosphere can prove a threat to the smooth running apparatus. The moisture may act on insulator or may be absorbed by the insulation. The process of absorption of moisture is known as Hygroscopicity. This affects the electrical properties adversely, however, there are insulating materials like paraffin, polythene, polytetra-floure ethelene, which are non-hygroscopic.

4. Effects on other Materials: 

The insulating materials are affected by the contact with the conducting and structural materials. If rubber is in contact with copper, chemical action takes place. To avoid it, a coating of tin is applied to copper before putting on the rubber insulation. In oil filled transformers and capacitors, the synthetic insulating oil reacts with the inner walls of the iron tank causing iron particles to mix with the oil and this can badly affect the insulating properties of the oil.

5. Ageing of Insulators: 

Ageing is the long time effect of heat, chemical action and voltage application. These factors decide the natural life of insulators and hence of an electrical apparatus.

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