TYPES OF HIGH VOLTAGE INSULATORS MADE BY ALINA V. IVANOVA GROUP 4 T 31
AIM OF PRESENTATION The aim for today’s presentation is to review types of insulators which are used in High Voltage Engineering. 2
OUTLINE q Basics • Resistance and Conductivity • Dielectrics q Types of insulators • Solids insulators • Gasses • Liquids • Insulation in electric wires • insulators used with high voltage power transmission q Conclusion 3
BASICS What is resistance and conductivity? Conductivity. Most metals are conductive, which means that electrons can freely flow to different atoms in a given direction. Metals have loosely bound, or free electrons which allow this to happen. Insulative materials on the other hand have tightly bound valence electrons. Dielectrics - these are materials that are do not allow electricity to flow through them (are insulators) however in the presence of an electrical field the material becomes polarized. This phenomena is useful in electronics. 4
Materials conductors, semiconductors Dielectrics liquid solid gas 5
SOLIDS Solid insulators include clay (ceramic)(porcelain), PVC, cresyl pthalate, DEHP and other plastics, glass (silica, soda ash and limestone), paper or cardboard, mica, teflon (PTFE), PFA (perfluoroalkoxy), rubber, wax and other. 6
GASSES Normally when you separate two high voltage conductors an arc forms in between in open air. In the utility industry we use special non-conductive gas in a compact encapsulated metal container to stop arcs from forming. Gas-insulated switchgear is designed to disconnect very high voltages safely. There are gas insulated transformers as well as other devices. 7
LIQUIDS In high voltage systems containing transformers and capacitors, liquid insulator oil is the typical method used for preventing arcs. The oil replaces air in spaces that must support significant voltage without electrical breakdown. Insulating Oil (Transformer Oil) - This petroleum product is used as an electrical insulator and thermal conductor. It conducts heat away from hot transformer coils. Some capacitors also use insulator oil. 8
INSULATION IN ELECTRIC WIRES Many types of rubber were used for electrical wiring and apparatus. Gutta Percha - a natural latex product was used for some time but was replaced by vulcanized rubbers. The end of the rubber era was sealed when chemists developed plastics that could withstand higher heat and resist corrosion better and any rubbers. Modern electric wires commonly use PVC plasticized with linear Phthalates and an over jacket of clear nylon for heat and oil resistance. Oil can dissolve plastics so it is important to have the nylon coating. Linear phthalate chords of today can stand heat up to 105 centigrade. There are many specialized types of wire with unique insulation including Polyimide. 9
INSULATORS USED WITH HIGH VOLTAGE POWER TRANSMISSION Insulators in the context of power transmission describe the support structures for wires and other devices. Insulators must support the conductors and withstand both the normal operating voltage and surges due to switching and lightning. Insulators are usually made of wet-process porcelain or toughened glass, with increasing use of glassreinforced polymer insulators. However, with rising voltage levels, polymer insulators (silicone rubber based) are seeing increasing usage. • Wood and glass insulators Dry lumber is an insulator to some degree, although it is not a good one, so early pioneers of electricity started using glass. • Ceramic High voltages created new problems for insulator design. Glass would crack apart with high temperatures and failed to withstand certain high temperatures, so the solution lay in ceramics. Chemists and material engineers helped design higher performance porcelain insulators with special coatings and designs. • Polymer insulators by nature have hydrophobic characteristics providing for improved wet performance. Also, studies have shown that the specific creepage distance required in polymer insulators is much lower than that required in porcelain or glass. Additionally, the mass of polymer insulators (especially in higher voltages) is approximately 50% to 30% less than that of a comparative porcelain or glass string. Better pollution and wet performance is leading to the increased use of such insulators. 10
CONCLUSION The insulators plays a vital role in electrical system. Insulators are used in all electrical devices from tiny capacitors to giant generators. Engineers need to understand how to design devices with the proper insulator. Unfortunately insulator failure is a primary reason why electrical devices stop working. 11
REFERENCES 1. Electrical Insulators - Edison Tech Center http: //www. edisontechcenter. org/Insulation. html 1. Wikipedia, the free encyclopedia, https: //ru. wikipedia. org 2. Pictures Google, https: //www. google. ru 12
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