Partial discharges in void defect of gas insulated switchgear insulator under standard aperiodic and oscillating switching impulses

This study focuses on partial discharges (PDs) in the gaseous void in an insulator under aperiodic switching impulse (SI) and oscillating SI (OSI). The PD measurements are carried out using a 110-kV GIS model with an artificial known void defect in a basintype insulator. Experiments show that the PD sequences under SI and OSI are composed of the main discharge, which occurs at the rising edges or the peaks of the applied impulse, and the polarity reverse discharge, which occurs at the falling edges or troughs. For a new sample, the 50% PD inception electric field (PDIE 50 ) under different stress types obviously decreases with increasing void radius, and their values follow the pattern PDIE 50, OSI > PDIE 50, SI > PDIE 50, AC . For an aged sample, the difference between the experimental PDIEs and the streamer inception value becomes close. The relationships between the time lag and the applied voltage can be calculated by the V–t curves, which roughly describe the distribution of the time lag under impulses. The experiment indicates that OSI can more easily excite PD compared with SI. Repeated tests show that the magnitudes and numbers of the main and reverse PDs gradually change as the test is repeated.