The main reason why there is a failure in the overhead line electrical insulation film is the flash over which occurs in between the line and earth during abnormal voltage in the system. When the flash over occurs, the huge amount of heat produced by arcing will cause puncher in the insulator body. Viewing this particular phenomenon the materials used for electrical insulator, it has to possess very specific properties.
Various Properties of Insulating Material
The materials which are typically used for the purpose of insulation are called insulating materials. In order to have a successful utilization, the material should have specific properties. Foremost it should be mechanically strong enough in order to carry tension and weight of the conductors. Second, it should have very high dielectric strength in order for it to withstand the voltage stresses happening in high voltage system. Third, it should possess high insulation resistance in order to prevent leakage current towards the earth. Another thing to remember is that insulating materials should be free from any unwanted impurities. Next, it should not be very porous. Although, there should be no trace of any entrance to the surface of electrical insulator so that the gases or moisture can enter in it. The physical and electrical properties of the material should also be less affected by the changing temperature.
Porcelain is deemed to be the most commonly used material as overhead insulator today. The porcelain is made of aluminum silicate. This silicate is mixed with feldspar, plastic kaolin and quartz in order to attain the final glazed and hardened porcelain insulator material. The surface of the insulator should also be glazed enough so that the water will not be traced on it. Porcelain should also be kept free from porosity since porosity is considered to be the main cause of deterioration of the material’s dielectric property. It should also be free with any kind of impurity and air bubble inside the material which can affect the property of the insulator.
Today, glass insulator has become popular in distribution and transmission system. Annealed tough glass is being used for insulating purposes. Glass insulator has also several advantages compared to the use of conventional porcelain insulator.
There still other kinds of insulators and these help in different applications.