Signal Processing Technique for AC Corona Pulses and Charge Computation

Abstract

Corona discharge has been one of the well-researched areas in the air breakdown study. The understanding of AC corona is mainly prompted to design proper hardware for the power systems. In the present study, the characteristics of AC corona current pulses is studied for a point to plane geometry (gap distance of 5 mm) under low pressure, room temperature condition, using a signal processing technique. High voltage varying from 1 kV to 15 kV is applied to the needle to generate the corona discharge at two different pressures of 1000 mbar and 500 mbar. The corona current pulses are captured across a resistor using a shunt box (which is EMI shielded) connected to a ground electrode. The characterisation of the captured pulses is done using signal processing techniques in MATLAB. The sinusoidal component of the AC corona current is filtered out using curve fitting and the high-frequency base noise is removed from the filtered waveform using thresholding. Different parameters like the number of pulses, associated charge during positive and negative half of the cycle, and phase distribution of the negative pulses are presented. Interestingly, it was found that the charge associated with the negative pulses was more at the low voltage condition and as the voltage increased, net charge during the ionization shifted towards positive. This study is thought to be useful in understanding the nature of the charges produced in the ionization via the corona pulses.