Gas-insulated switchgear (GIS) is often subjected to overvoltages from lightning strikes

transient switching operations

and the superposition of power-frequency impulse voltages. The presence of foreign object defects along the insulation components of GIS significantly increases the probability of discharge

posing a serious threat to the safe operation of the equipment. This study establishes an experimental platform for high-frequency superimposed impulse voltage

aiming to investigate the statistical characteristics of flashover paths and discharge voltages along the surface of GIS insulation components caused by foreign objects. By comparing and analyzing the influence of superimposed phases and foreign object sizes

this study aims to reveal the flashover mechanism along the surface under high-frequency superimposed impulse voltages. The results indicate that

under different superimposed phases and polarities

flashover paths exhibit two typical patterns: "vertical development" and "bypass"

significantly impacting the superimposed discharge voltage U50%. When subjected to reverse polarity superposition

the flashover path develops along the centerline of the insulator electric field

with a discharge emission angle θ≤25°. This indicates that defect-induced space charge promotes discharge propagation under superimposed voltage. At this point

the flashover voltage U50% experiences a significant decrease compared to the lightning impulse breakdown voltage Us

with a high flashover voltage variation rate k of up to 27.8%. Conversely

under same-polarity superposition

the flashover path tends to "bypass" the area in front of the defect

resulting in a notably increased discharge emission angle θ ranging between 40° and 90°

with higher dispersion. In this scenario

defect-induced space charge impedes discharge development under superimposed voltage

leading to a minimal reduction in U50%. Furthermore

particle curvature significantly influences the flashover path and discharge voltage

and sharper particles result in a higher k value. When AC(φ=180°)/+LI

as the particle curvature increases from 0.15 mm to 0.5 mm

the k value decreases from 15.8% to 11.1%. This study provides insights and a basis for enhancing the insulation reliability of GIS under high-frequency superimposed impulses.