Method of Controlling Corona Effects and Breakdown Voltage of Small Air Gaps Stressed by Impulse Voltages

This paper investigates the influence of a resistor on the dielectric behavior of an air gap. The resistor is connected in series with the air gap and the latter is stressed by impulse voltage. Air gap arrangements of different geometry with either the rod or the plate grounded are stressed with impulse voltages of both positive and negative polarity. The resistor is connected in series with the air gap in the return circuit connecting the gap with the impulse generator. The method followed involves the investigation of the graphs of the charging time concerning the air gaps capacitances, in connection to the value of the resistor, the geometry of the gap, the effect of grounding and the polarity effect. It is determined that the charging time of the air gap increases, as the value of the resistor increases. It is also determined that the peak voltage value of the fully charged air gap decreases as the value of the resistor increases. The results of the mathematical and simulation analysis are compared with the results of the oscillograms taken from experimental work. In addition and consequently to the above results it is concluded from the experimental work that the in series connection of the resistor in the circuit has significant influence on corona pulses (partial discharges) occurring in the gap and on the breakdown voltage of the gap. A new method of controlling the corona effects and consequently the breakdown voltage of small air gaps stressed by impulse voltage of short duration in connection to the ground effect and the polarity effect has arisen. Furthermore through mathematical analysis of the charging graphs obtained from simulation and experimental oscillograms there was a calculation of the values of the capacitance of the air gaps in relation to their geometry and the results were compared to the values calculated with mathematical analysis