Influence of a dielectric barrier on the dc and ac breakdown strength of a point-to-plane gap in air

The breakdown voltage of an air insulated nonuniform field gap can be increased by placing a barrier, i.e. a plane sheet of insulating material, between the electrodes normal to the gap axis. This paper reports on the results of an experimental study of the influence of the location of a barrier on the breakdown voltage of a number of point-to-plane gap lengths, stressed with dc voltage of both polarities and 60 Hz ac voltage. The effect of a barrier on the ac corona current and the influence of the area of the barrier surface on the magnitude of the breakdown voltage were also studied. The results show that instead of enlarging insulation clearances in equipment with non-uniform electric fields, the application of a barrier may be a practical alternative.