Influence of sand/dust contamination on the breakdown of asymmetrical air gaps under switching impulses

This paper discusses the influence of airborne and surface-adhering sand/dust contamination on the breakdown characteristics of asymmetrical air gaps when subjected to standard switching impulses of both polarities. Extensive measurements of breakdown voltages and breakdown times are carried out under clean and polluted conditions using rod-plane and sphere-plane gaps. When positive switching impulses are applied to gaps /spl les/1.8 m, the presence of sand/dust particles /spl les/150 /spl mu/m diameter and /spl les/2 g/m/sup 3/ concentrations have insignificant influence on the breakdown characteristics of the air gaps. However, the presence of such particles can greatly affect the breakdown characteristics for negative switching impulses. Under such conditions, the particles can decrease V/sub 50/ by /spl les/40% for gaps with field factor f /spl les/3.5. For gaps with 3.5>