Abstract
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<f<12, the contamination can increase V/sub 50/ by /spl les/80%. For more nonuniform field gaps, V/sub 50/ values for clean and contaminated conditions are similar. The particles can also significantly influence the breakdown time lag characteristics under negative switching impulses. The observed effects are primarily caused by sand/dust particles which settle on the cathode, while the particles present in the interelectrode gap or on the anode have very little influence.< >