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

The authors review the important parameters of particles which are present in the environment when sand/dust storms occur. Basic features of the experimental system are summarized. Extensive measurements of breakdown voltages and times to breakdown are carried out under clean and polluted conditions using rod-plane and sphere-plane gaps. It is shown that when positive lightning impulse voltages are applied to asymmetrical gaps from 5 cm to 2 m, the presence of sand/dust contamination can cause a breakdown voltage reduction. However, the presence of particles can greatly affect the breakdown characteristics of rod-plane and sphere-plane gaps under negative lightning impulses. For gaps with moderately nonuniform field distributions, the particles can decrease V₅₀ by ⩽40%. If the field distribution is more nonuniform, the contamination can increase V ₅₀ by ⩽50%. For highly nonuniform field gaps, V ₅₀ values for clean and contaminated gaps are approximately similar. Such effects are primarily caused by particles which settle on the cathode