Time-lag of void discharges was measured in order to establish thephysical model for the formation of partial discharge pattern under ACvoltages. The measurement with step voltages, using CIGRE Method IIelectrode system, showed that the statistical distribution of thedischarge time-lag depends on the applied voltage, the time lag beingshorter with increasing the voltage. In most cases, the statisticalscatter of the time lag under the same step voltage fitted with astraight line on the Laue Plot, indicating that the time-lag follows theexponential distribution. The characteristic time-lag decreased with themagnitude of step voltage, and followed the inverse power low. Thedecline of the “time-lag vs. voltage” plot was correlated tothe partial discharge pattern under the AC voltage. Moreover, thetime-lag distribution with different kinds of specimens were comparedtogether, in order to explain the difference in partial dischargepattern under AC voltage. It was concluded that the discharge time-lagplays an important roll in generating the partial discharge pattern, andthat some features of the pattern can qualitatively be explained by thevoltage dependence of the discharge time-lag
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