Influence of voltage waveforms on partial discharge characteristics of protrusion defect in GIS

The CIGRE WG D1.03 has indicated the breakdown voltage of GIS with protrusion defect under standard lightning impulse (LI) voltage is significantly smaller than that under standard switching impulse (SI) or AC voltage, and LI withstand test is more efficient to find protrusion defect. The question is that whether the partial discharge (PD) inception voltage of protrusion defect under LI is also lower than that under standard switching impulse or AC voltage. In order to understand the relations between voltage waveforms and protrusion defect, three kinds of protrusion with different curvature radius are designed, namely, 0.025 mm curvature radius, 0.25 mm curvature radius, and 0.5 mm curvature radius, and the PD characteristics of protrusion defects are measured under four types of voltage waveforms (standard lightning impulse, standard switching impulse, oscillating switching impulse (OSI), AC voltage), and the influence of voltage waveforms on PD characteristics of protrusion is analyzed. The results indicate that, for protrusion with 0.025 mm curvature radius, the steeper the impulse voltage front is, the lower PD inception voltage of protrusion defect is, and PD under LI has higher detection sensitivity to protrusion compared with AC voltage and SI. While for protrusions with 0.25 mm curvature radius and 0.5 mm curvature radius, the steeper the impulse voltage front, the higher the PD inception voltage of protrusion defect is, and PD under LI has lower detection sensitivity of protrusion with 0.25 mm and 0.5 mm curvature radius compared to AC voltage. As PD exacerbated, the shape changes occur in the q-φ scatter plot, N-φ histogram under oscillating switching impulse voltage, and q-1 scatter plot and N-1 histogram under non-oscillating impulse voltage, which can be used as important criterion in assessing the severity levels of the partial discharge triggered by protrusion under impulse voltage waveforms.