Design Of An Insulator example essay topic
362 words
Insulation Theory Insulators are the devices used on electricity supply networks to support, separate, or contain conductors at high voltage. All insulators have dual functions, mechanical and electrical, which commonly present conflicting demands to the designer. The most serious complicating factor is the impossibility, in practice, of providing an ideally non conductive element. This is so because all insulators have external surfaces, which will become contaminated to some extent in service. The contamination will carry leakage current: the surface layer, on a typically polluted insulator, will contain inert material matter, electronic-conductive dusts like carbon or metal oxides, soluble salts, and water. This layer will behave as a highly variable and nonlinear resistor, in most cases unstable in the presence of electric fields. The leakage current that it carries will give rise to heat, electrochemical products of electrolysis, and electrical discharges. Thus, leakage currents and its consequences, largely govern the design of an insulator, especially one which is to be used outdoors in atmospheric wetting and pollution. There are different types of insulators; the principle classes of insulators are available in Table 1 (Appendix A-Tables). Their main functions, as ties in tension, as struts in compression, as beams in bending, and as containers in hoop-stress are usually supplemented buy others. The considerations that decide how an insulator shall be made up and how it will perform in service are three: the properties of the materials within it, its ability to operate in adverse weather and contamination, and its cost.
The three main materials in any insulator are the dielectric, the terminations that couple the dielectric to the mechanical structure, and the intermediaries such as cements, lubricants, or paints. The dielectrics, commonly porcelain, glass or polymer, are required to hold off the applied potential difference, for several decades without failure. They must also resist impulsive voltages arising from lightning or switching operations without puncture. Since the surfaces of the dielectrics will always be conductive to some degree because of humidity and dirt, a good resistance to electrical discharges and electrochemical products, as well as to normal corrosion, is also essential.
