INFLUENCE OF DUST POLLUTION ON THE SWITCHING IMPULSE BREAKDOWN OF SPHERE GAPS

This paper discusses the effect of dust contamination on the breakdown characteristics of sphere-sphere air gaps when subjected to standard switching impulses of both polarities. Spheres having diameters (D) of 125 mm and 250 mm were used with d/D ratio (d = gap length) in the ra nge of 0.2 to 1.5. It is shown that, for gaps with 0.2 less than or eq ual to d/D less than or equal to 1, the dust pollution can reduce the 50% breakdown voltages (V-50) and the scatter in breakdown voltages as well as in breakdown time lags for both polarities of impulse voltage s. For d/D > 1, the dust particles can increase V-50 values under some conditions. It is further shown that for d/D less than or equal to 0. 5, the region where sphere gaps are used for voltage measurements, the influence of dust particles on breakdown characteristics is similar t o the effect of ultraviolet irradiation.