The Polarity Effect and the Corona Current in Small Air Gaps

Abstract. A new approach of the Polarity Effect in connection to the Corona Current and the Ground Effect in small rod-plate and rod-rod air gaps is presented. The influence of the polarity of the applied voltage to the corona onset voltage or the breakdown voltage of small rod-plate and rod-rod air gaps is investigated. The influence of the grounding of one of the electrodes, to the field distribution, and consequently to the corona onset and the breakdown voltage of small air gaps, is also investigated by simulation analysis along with experimental work. This phenomenon is the Ground Effect, and is quite different from the Polarity Effect, though slightly influenced by it. The inhomogeneity of the electric field and the maximum values of the field strength in a rod-plate and rod-rod air gap are analogically higher when the plate is grounded and lower when the electrodes are symmetrically charged, or the rod is grounded. The values of the corona onset and the breakdown voltage in small air gaps are analogically lower for the arrangement with the plate grounded. Correspondent relations are valid for the rod-rod arrangements. In longer air gaps the corona current appears, the Polarity Effect becomes very intense and the Ground Effect is overlapped. Relations between the values of the breakdown voltage, the polarity of the applied voltage, the corona current through the gap and the way the gap is grounded are established. The principle of action-reaction is valid. “The corona current reacts against the action of the field to produce corona charges and makes the field less inhomogeneous”.