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An insulator is a poor conductor of heat or electricity due to its property to resist the flow of electrical charges. Ideally speaking, a perfect insulator for electrical applications would be a material that is totally nonconducting; however, such a material with total nonconducting property does not exist.
To be precise , the materials used as insulators do conduct some electricity, and have a resistance to the flow of electric current as much as 2.5 × 1024, which is greater than good electrical conductors such as silver and copper.
Usually, materials that are good conductors have a large number of free electrons (electrons not tightly bound to atoms) available to carry the current. On the contrary to this, good insulators have few electrons. Besides this, some materials, like silicon and germanium, which have a limited number of free electrons, are semiconductors and form the basic material of transistors..
High-voltage insulators
For high-voltage power transmission, high-voltage insulators are used. High-voltage insulators are made from glass, porcelain, or composite polymer materials. Porcelain insulators are made from clay, quartz or alumina and feldspar. For high mechanical strength, Alumina insulators are used.
Nowadays, many electric utilities have begun converting to composite insulators as they are are less costly, lighter weight, and they have excellent hydrophobic capability. Composite Insulators consists of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or EPDM. This combination makes them ideal for service in polluted areas.
Low-voltage insulating materials
In order to reduce the risk of a person coming in contact with live wire, flexible insulating materials such as PVC (polyvinyl chloride) or neoprene are used.
Depending upon the type of application, insulating materials for a partcular application is decided. For instance, polyethylene and polystyrene are used in high-frequency applications while mylar is used for electrical capacitors. In the same lines, insulators are also selected according to the maximum temperature they will encounter. For high-temperature of 175 degree celsius to 230 degree celsius , teflon is used. Adverse mechanical or chemical conditions may call for other materials. Nylon has excellent abrasion resistance, and neoprene, silicone rubber, epoxy polyesters, and polyurethanes can provide protection against chemicals and moisture.
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