A. Winter

Stationary resistive field distribution along epoxy resin insulators in air under DC voltage

The stationary resistive field distribution on the gas-solid interface along epoxy resin insulators is theoretically and experimentally investigated. Due to the phenomenon that the charge carriers necessary for the conduction process originate from natural ionization and a constant generation rate is assumed, the resulting electric conductivity of gases under dc voltage stress is nonlinearly depending on the field strength. A simulation model which considers the relevant characteristic is used to calculate the electric field in gas-solid insulation systems. The influence of the ion pair generation rate of the gas, the electric field strength and the surface conductivity of an insulator on the resistive field distribution is investigated. The results are compared to simulations, in which the electric conductivity of the gas is assumed to be constant. The simulations are verified by measurements of the surface potential along an epoxy resin insulator under dc voltage.

Transient field distribution in gas-solid insulation systems under DC voltages

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF6 as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air.