Flashover characteristics of long air gaps with negative switching impulses

The electrogeometric model (EGM) proposed by Armstrong and Whitehead has been used to calculate the lightning shielding features of transmission lines. While the striking distance equation in the EGM uses the 50% flashover voltage characteristics of negative switching impulses for rod-rod gaps, those characteristics for long air gaps have not been sufficiently examined. The present study has therefore focused on clarifying the 50% flashover characteristics of negative switching impulses for long air gaps. Consequently, saturating characteristics have been obtained for rod-plane gaps compared with almost linear characteristics for rod-rod and rod-conductor gaps. Furthermore, new knowledge was obtained indicating that, for air gaps of around 4 to 5 m, the 50% flashover voltage may possibly be lower for rod-plane gaps than for rod-rod and rod-conductor gaps.