Experimental investigation on flashover characteristics of hollow porcelain insulator under extreme rainfall

Abstract This paper deals with the effects of rain conditions and shed parameters on flashover characteristics of hollow porcelain insulators through conducting artificial rain tests under extreme rainfall. And the effects of water droplet deformation on inter-shed discharge are examined especially. The results show that the rain flashover voltage gradient along the insulation height falls with the rise of rainfall intensity due to the increase in the maximum deformation length of water droplet, which can bring about two kinds of inter-shed discharge modes under different rainfall intensity. The fact that the maximum deformation length of water droplet is barely influenced by rainwater conductivity determines the consistency of inter-shed discharge modes under different rainwater conductivity. The rain flashover voltage gradient along the insulation height decreases with the rising rainwater conductivity since the insulator surface resistance falls with rainwater conductivity. Moreover, shed spacing can influence inter-shed discharge mode, which is reflected in the diverse direction of the discharge propagation at water droplet end under different shed spacing. The length of air gap on the breakdown path increasing improves rain flashover voltage gradient along the insulation height as shed spacing rises. However, the inter-shed discharge mode is independent of shed overhang. The rain flashover voltage gradient along the insulation height rising with shed overhang is attributed to the increase in the leakage distance along the shed surface. This work clarifies the inter-shed discharge mode of rain flashover and can provide valuable support for the shed design of insulators in extreme rainfall areas.