Polarity effect on corona discharge of needle-plane electrodes and audible noise under DC voltage

The corona discharge and audible noise in different polarities have different characteristics and rules. The experiment of sing point corona discharge under DC voltage was developed and the sound pressure produced by corona discharge was measured. The amplitude and pulse characteristics of needle-plane corona discharges were studied. The sound pressure in time domain was measured by capacitor microphone. The discharge current and sound pressure waveforms in different voltages and polarities were obtained. The research results indicate the DC corona discharges were composed of a series of pulsed discharges. The rising edge and pulse width of single discharge pulse have relation to discharge voltage and electrode polarity. The amplitude and pulse width of current pulse in positive corona discharge is higher than that in negative corona discharge. The corona discharge produces the sound pressure with a microsecond pulse lagging behind the single discharge pulse in their waveforms. The time delay between current pulse and sound pulse is mainly caused by sound propagation time from discharge spot to measurement spot. Whether there is sound pulse is mainly decided by the amplitude and pulse width of corona discharge current. The audible noise has positive correlation with the sound pressure. So the audible noise produced by positive corona discharge is higher than that produced by negative corona discharge. At the same time, the sound pressure has relation to the discharge repetitiveness. The research result provides the foundation to go deep into the audible noise mechanism of transmission lines.