Critical switching impulse strength of long air gaps: modelling of air density effects

A physical modelling approach is presented to investigate the effect of reduced air density on leader inception and sparkover of long air gaps under positive switching impulses with critical front time. The model accounts for the effect of air density on continuous leader inception voltage, leader length, and sparkover voltage. The results of the model provide critical positive switching impulse air density correction factors for rod-plane, rod-rod, conductor-plane, conductor-rod, and conductor-tower window gaps over a wide range of gap distances and relative air densities. The model findings were extensively checked against previous experimental results with quite satisfactory agreement