Research on effectiveness of lightning impulses with different parameters for detecting protrusion defects in GIS

The focus of this paper is on the effectiveness of lightning impulse (LI) with different parameters for detecting protrusion defects in gas insulated switchgear (GIS). The study examines the 50% (U₅₀) breakdown probability for typical protrusion defects on the conductor of a 363 kV class GIS. A quantitative method is developed to predict breakdown voltage, calculate minimum detectable length of defect, and express the effectiveness of the LI test. The results show that there is little difference of U₅₀ between aperiodic and oscillating LI. Corresponding detecting effectiveness decreases for LI with long wavefront, which is expressed quantitatively by detectable area. The critical defect length detected increases with increased wavefront. This study provides a general method to express the effectiveness of LI with different parameters for detecting protrusion defects and it support the LI test for on-site testing of GIS.