| Popis: |
The physical processes occurring during partial discharges in voids in dielectrics have been studied utilizing fast oscilloscopic techniques to observe the buildup and decay of current as a function of time for single discharges. A key parameter is the overvoltage at breakdown, determined for time-dependent voltages by the rate of rise of voltage and the statistical time lag. Two distinct types of discharge have been identified, named ?Townsendlike? and ?streamerlike?, and mechanisms responsible for their development have been proposed. The relationship between current-time pulse shapes as well as discharge magnitudes (charge per discharge) and various parameters such as overvoltage, void size, and dielectric thickness and permittivity have been explored. The conditions governing the transition between the two types of partial discharges have been examined quantitatively. The relationship between streamer propagation and Lichtenberg figure development has been studied. Measurements of statistical time lags for partial discharges have been made and significant paramters examined. The usefulness of these results in connection with future studies of chemical degradation of insulating materials are discussed. |
