Partial discharge detection and analysis of needle-plane defect in SF6 under negative oscillating lightning impulse voltage based on UHF method

Gas insulated switchgear (GIS) is used in power system more and more widely. With the increased voltage level of power system, field impulse voltage withstand test becomes increasingly important. It would be beneficial for a comprehensive insulation evaluation to carry out the detection of partial discharge (PD) under impulse voltage withstand test in field. Metal protrusions or particles on HV conductor are typical defects in GIS and are critical at lightning impulse voltages. This paper therefore aims at PD characteristics study on needle-plane defect under oscillating lightning impulse (OLI). PD detection system was established based on ultra-high frequency (UHF) and pulse current detection. Then, the PD of a needle-plane defect under negative OLI was measured. The relation between statistical time lag, PD amplitude, PD times and the applied voltage was analyzed respectively based on UHF detection. The results show that UHF detection has high sensitivity and it is suitable in field impulse voltage withstand test. PDs occur around each wave peak of the applied voltage. With the increase of peak voltage, PD magnitude and PD times in each oscillation cycle both increase linearly. Further analysis indicates that the occurrence and development of PD under negative OLI can be interpreted by electron emission from metal surface, field detachment from negative ions and corona stabilization effect. This approach is valuable for PD measurement and analysis in field impulse voltage withstand test for GIS.