Electrode protrusions and particle chaining as factors affecting the dielectric strength of air

Electrode protrusions and free particles have been demonstrated to reduce dramatically the breakdown voltage of insulating fluids. This paper examines two factors which affect the dielectric strength of gaseous insulators: (i) shape and size of electrode protrusions; and (ii) particle chain formation. A computer program, based on the boundary element method, was employed for the computation of the electric field modified by an electrode protrusion and/or a particle chain. The results regarding field enhancement were used as input data of another program that evaluated the dielectric strength of the air-gap. Two types of protrusions were studied: hemispheres and hemispherically-ended rods. One to ten conductive spheres were considered to be attracted to such protrusions and chain at the top of them. The computations showed that the large protrusions are more harmful than the small ones and that the dielectric strength of the air-gap decreases with the number of particles in a chain.