Characteristics of negative corona discharge using CWT with and without airflow

The Trichel pulse (TP) corona generated in the negative corona discharge has a regular interval and repetition of similar waveforms in nonuniform electric field in a needle-plane gap. An electron avalanche causes the TP. Its repetition is determined by accumulation of negative ions near a needle tip. The electric field intensity near a needle tip is weakened by the negative ions accumulated near the tip. Hence, it is required to clarify the influence of accumulated negative ions on the electric field intensity. We propose to use the continuous wavelet transformation (CWT) technique to study the dependence on both voltage and airflow, and the characteristics of the TP. In this study, the waveform of the TP is measured with a velocity of airflow from 0 to 7 m/s. From the experimental results, it is shown that the region of accumulated negative ions exists within 1 mm from the tip of needle electrode. Therefore, to understand the effect of accumulated negative ions near a needle tip, the authors investigated the influence of accumulated negative ions with and without airflow blown within 1 mm from the tip of the needle electrode using CWT. The repetition rate decreases with decreasing the applied voltage, and with increasing the velocity of airflow in front of the needle tip. The wavelet coefficients with airflow are larger than without airflow at 100 and 250 MHz; but 10 MHz, and the pulse interval for the wavelet spectrum between peaks with airflow is wider than without airflow. The characteristics of the TP waveform are well explained with both the wavelet coefficient and the averaged wavelet spectrum peak interval