Partial discharge characteristics over SF₆/epoxy interfaces under impulse voltage

Gas insulated switchgears (GIS) have been widely used due to their high reliability, low maintenance and compact size. The field experiment is an important step to ensure the safety of GIS. The 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. This paper reports on experiments to study surface discharge over SF ₆/epoxy under impulse voltage. The TJ (triple-junction) model was used to study the characteristic of partial discharge (PD). The PD signals under four types of impulse voltages were detected by electrical methods. The 50% probability PD inception voltage (PDIV₅₀), time lags and maximum discharge magnitude were analyzed as a function of gas pressure. The PD characteristics under AC voltage were investigated for comparison. The results indicate that the PD signals under impulse voltage can be detected using electrical method, the number of discharges under oscillating impulse voltage was significantly larger, which was due to the influence of source oscillation. The oscillating lightning impulse has the lowest impulse ratio and it is recommended as the best test waveform choice for the field impulse withstand test with PD detection.