Document Type : Review Articles
faculty of mechanic,power and computer engineering, department of power and control, islamic azad university,science and research branch, tehran iran
Application of sufficiently intense electric fields to insulators induces finite currents and then the insulators become metallic. This phenomenon is called dielectric breakdown and known as a fundamental non equilibrium and nonlinear transport phenomenon in solids. Partial discharge (PD) is a small electrical avalanche caused by locally disrupted electric fields in dielectric materials, and is known to be one of the major factors which accelerate the degradation of electrical insulation. Pollution is the most important cause of external electrical failure of the insulator, followed by the operation of relays and the exit of transmission lines from the power grid. It is believed that the flash over and partial discharge phenomena are strongly related to environmental conditions such as temperature, humidity, pressure, pollution's, and even space charges. In this review paper, we will identify the types of insulators associated with pollution sources and present laboratory results while defining partial discharge and its effects on equipment.