Air Clearances for Electric Railways: A Study of the Breakdown Voltage of Rod-Plane Gaps in a Variety of Atmospheric Conditions

A study has been made of the electric strength of air gaps for the Canadian 50 kV railway system. Tests were made on a rod-plane gap using switching and lightning impulses, 60 Hz and combined impulse and 60 Hz waves. The effects of clean and salt-water fog and dust contamination as well as exhaust fumes were investigated. The influence of water droplets falling from one electrode was also determined. Of these, the most important factor in reducing the ac strength of the air gap was exhaust fumes, which brought down the strength by as much as 20 percent.