Optimization and prediction of dielectric behavior of small air gaps stressed by DC voltages

The present paper aims to the investigation of the methods used to optimize and predict via simulation the values of the Corona onset voltage, the Corona current and the Breakdown voltage in small rod-plate air gaps when stressed by dc voltage. The main factors which influence greatly the distribution of the electric field in the gap, and hence the above values are the geometry and the selection of grounding and charging of the electrodes, (ground effect), the polarity effect, the gap length, and the Corona effects appearing prior to breakdown. Combining theoretical, simulation and experimental work, it is resulted that: a) The electrode chosen to be ground, strongly influences the distribution of the field and the Corona effects and hence the values of the Corona onset, the Corona current and breakdown voltage. b) Minimum values of the Corona onset voltage and maximum values of the Corona current and the breakdown voltage were defined in relation to the geometry of the gap and in connection to the effects of grounding, polarity and Corona current. c) It is proven that it can be predicted by means of simulation analysis whether an air gap will lead to Corona or breakdown, and it can also be predicted which specific arrangement of a rod-plate air gap must be chosen in order to maximize the Corona current when a voltage of a certain value is applied.