Partial Discharge in High Voltage Insulating Materials

High voltage transmission has been chosen in electric power system due to its capability to transfer a large amount of electric power. Several key equipments such as generator, transformer, GIS, cable and insulator play important role in determining the reliability of the power system. The high voltage equipments in general contain gas, liquid or solid insulation. Defects and a particular condition may lead to extremely high electric field. Particularly at interfaces between gas and solid and liquid insulations, the excessive electric field may cause the breakdown of the gas while the liquid and solid insulations are still able to withstand the electric field. This phenomena is referred as partial discharge (PD). Partial discharges in high voltage equipments for long time may degrade the quality of the insulation and at the same time the appearance of discharges can be used as diagnostic signal for assessing the condition of the insulation inside the high voltage equipments. Partial discharge is an important subject investigated by many researchers and discussion in many international conferences as well as international journals or transactions. This paper discusses the measurement and experimental results and analysis on time-resolved partial discharges in gas, liquid and solid insulation. The partial discharges are presented in various distribution such as ɸ-q-n, ɸ-n and three dimensional distribution. Here ɸ is phase angle, q is the discharge magnitude and n is the discharge number. Based on the partial discharge data, diagnosis methods of high voltage equipments as also presented.