Partial discharges in SF₆ gas filled void under standard aperiodic and oscillating switching impulses

Partial discharges (PDs) in the void filled with SF₆ gas were investigated under IEC60060-3 standard aperiodic switching impulse (SI) and oscillating switching impulse (OSI). Some single discharges and discharge sequences with different characteristics were detected. A theoretic voltage-time lag (V-t) curve of the first discharges was proposed and proved to be effective in analyzing the occurrences of the first discharge by comparing the calculated V-t curve and experimental V-t point distribution under test situations. The PD activity in terms of the discharge magnitude and number had significantly associations with the gas pressure in the void and the void shape (dimension ratios). Furthermore, a hypothetical physical model with charge memory effect was proposed to interpret the mechanisms underlying the different PDs in sequence under the two impulses, by which the simulation was carried out, showing a roughly consistency with the measured distribution.