Discuss description of insulating materials on the basis of physical and chemical structure
Insulating materials, on the basis of their physical and chemical structure may be described in various categories as follows:
1. Fibrous materials: They are derived by animal origin or from cellulose that is the major solid constituent of vegetable plants. Therefore majority of materials are from cellulose. It includes paper, card- board, wood, cotton, silk and jute.
2. Impregnated fibrous material: These fibrous materials are impregnated along with appropriate impregnated oil, epoxy and varnish- resin to enhance its thermal, hygroscopic and chemical properties.
3. Non-resinous materials: Solid or semisolid insulations that are directly available in nature and are organic based come in this class. Such materials are mineral waxes, bitumen, asphalts and chlorinated naphthalene.
4. Insulating liquids: Apart from working as insulation, they fulfil other significant requirements as they offer good heat dissipation media, they used for extinguishing arcs in specific applications like circuit breakers. They comprise vegetable oils, mineral insulating oils, synthetic liquids and fluorinated liquids.
5. Ceramics: They are materials made by high temperature firing treatment of natural clay and specific inorganic matters. All are used as dielectric in capacitors and as insulators.
6. Mica and mica products: This is an inorganic mineral and one of the best natural insulating materials obtainable. Mica is used as a dielectric in capacitors, like insulator. Several of the mica products are glass- bonded mica, mica paper, and synthetic mica and manufactured mica.
7. Asbestos and asbestos products: These are strong and flexible fibres. This finds extensive use in electrical equipment as insulation due to its capability to withstand very high temperatures. Several of the asbestos products are as: asbestos roving, asbestos tapes and asbestos cement and asbestos paper.
8. Glass: It is an inorganic material made by the fusion of various metallic oxides. This is normally brittle, hard and transparent. Glass gets its use in electrical industry due to its low dielectric loss, good mechanical strength and slow ageing. It is used in electrical- bushings, fuse bodies, radio, television tubes and insulators.
9. Natural and synthetic rubber: Natural rubber is acquired from the milky sap of rubber trees. This finds limited applications since this is rigid when solid, sticky while warm and gets oxidised, while exposed to atmosphere. Therefore, Synthetic rubber is of different types as butadiene rubber, chloroprene, silicon rubber and butyl rubber, that are acquired by the polymerisation. This rubber, are used as insulating material for cables and wires. This is also used as jacketing material for cables.
10. Insulating resins and their products: Plastic or resins are of two kinds - one derived by plant and animals the other synthetic acquired from chemical reactions. Natural resins are used as binder material. This is used as thickening agent for manufacture of mineral insulating oils. This synthetic resin is used as insulation, instrument mountings and manufacture of switches, electrical bushings, television cabinets and radio.
11. Laminates, enamels, varnishes and adhesives: Laminates are multiple, sheets of insulating materials or thin layers as that of mica, cloth, paper and glass, bonded together. Adhesives are a type of material compositions needed to carry out bonding in between two or more solid surfaces. They are used in the manufacture of laminated boards, rods, coil winding cylinders and tubes and particular shaped insulators. Enamel is a fusible insulated coating of several organic base materials that is normally applied on conducting surface. Enamel gets extensive use in coating wires utilized for the windings of low rated motors, transformers, different types of instrument. Varnish is a liquid, that applied to a surface dries when resulting in hard shining coating that is resistant to water and air. Lacquer is utilized for protecting wood and metal surface from external weather circumstances.