Partial discharge initiated by grounding metallic protrusion in GIS: Light and electromagnetic emission phenomena and discharge evolution process

Grounding metallic protrusion defect is one of the most common and hazardous grounding electrode faults in GIS equipments. The present research is designed to explore the evolutionary process of the partial discharge (PD) provoked by grounding metallic protrusion defect in GIS through observing the light and electromagnetic emission phenomena alongside the PD development. On the 252 kV GIS experiment platform, long term tests were undertaken to observe the entire PD evolution process from its very initiation till the eventual flashover as the applied voltage gradually increased. Ultraviolet camera and photo multiplier tube (PMT) were employed to document light emission phenomena while ultra high frequency (UHF) sensor was engaged to monitor the electromagnetic emissions during the partial discharge evolution process. It is observed that light emission appears to be inhomogeneous throughout the PD evaluation process. As partial discharge exacerbates, the phase distribution is widening and corresponding changes show up in the PD statistical spectrums. The phenomena of light and electromagnetic emission indicate that the partial discharge triggered by grounding metallic protrusion evolutes from inception phase to the developing phase and the threatening phase till flashover. It is suggested that these observed phenomena and inferred PD evolution stages could serve as useful support for the diagnosis and assessment of severity levels of the partial discharge triggered by grounding metallic protrusion defect in GIS.