Detection and Recording of Partial Discharges Below the So-called Inception Voltage with Point-Plane Electrode Arrangements in Air

The problem of insulation damage from partial discharges below the so-called inception voltage has not yet attracted much attention. Indications of possible damage exist from previous research. In this paper, the possibility of existence of such phenomena is investigated with small air gaps and point-plane electrode arrangements. It is shown that random discharges below inception voltage may exist. Such discharges are registered and their waveforms are discussed. Experimental evidence is offered that discharges change from the pulse-type to a pulseless-type as the air gap becomes larger. Phenomena affecting in some way the insulating systems below inception may help us to better understand the mechanism of small current flow at relatively low voltages and may contribute to a better formulation of dielectric materials.