Partial discharge characteristics and mechanism in SF6 Gas under oscillating impulse voltages

Impulse voltages strongly affect the reliability of gas insulated switchgear (GIS) under actual operational conditions. The alternating-current (AC) withstand voltage test and its corresponding partial discharge (PD) measurement are inadequate for the detection of all the hidden flaws in GIS. Such inadequacy can be compensated by additional impulse withstand voltage test and its PD detection measurement. However, the bulkiness and inefficiency of aperiodic impulse voltage generator makes it unsuitable for on-site application. Therefore, in practical tests, oscillating impulse voltage is generally adopted instead of aperiodic impulse voltage. This paper reports on experiments to study corona discharge in SF
₆
gas under two types of oscillating impulse voltages. The needle-plate gap model was used to study the characteristic of PD. The PD signals were detected by electrical and optical methods. Oscillatory phase-resolved partial discharge (OPRPD) spectrum under oscillating impulse voltage was introduced to describe the PD characteristics. The physical mechanisms of the PD under the two oscillating impulse voltages were discussed. The PD characteristics under AC voltage were investigated for comparison. The experimental results revealed that the PD development process under the oscillating impulse voltage was mainly dominated by a combination of high-frequency and precursor mechanisms. The difference of the PD characteristics under the oscillating impulse voltages and AC voltage were also presented.