Experimental Study on Negative Corona Characteristics in a Needle-to-Plate Gap under Unipolar Positive Voltage and Negative-to-Positive Polarity Reversal Conditions
Abstract
To investigate the response of corona discharge at a needle tip under rapidly varying thunderstorm-like electric fields, a needle-to-plate test platform capable of polarity reversal was developed. Unipolar positive DC voltage and negative-to-positive polarity-reversal voltage were applied to the upper plate, and the induced current on the grounding line of the needle tip mounted on the lower plate was measured and analyzed. The results show that, under unipolar positive voltage, the negative corona current at the needle tip exhibits a clear stage-like evolution as the voltage increases. No identifiable corona pulse is detected at +10 kV. At +15 kV, a few isolated pulses begin to appear. At +20 kV, the discharge develops into a relatively stable pulse train. At +25 kV, the pulse frequency rises significantly and local pulse overlap becomes evident. At +30 kV, the continuous component is enhanced and the waveform gradually evolves toward a quasi-continuous negative glow state. Based on the absence of obvious pulses under the unipolar +10 kV condition, a polarity-reversal test from -10 kV to +10 kV was further carried out. The results indicate that distinct transient pulse peaks appear after reversal, demonstrating that polarity reversal can promote earlier onset of negative corona under low-voltage, near-threshold conditions. This phenomenon is mainly attributed to local electric-field distortion at the instant of reversal and the memory effect of residual space charge left from the preceding polarity stage. The results suggest that when the thunderstorm background electric field changes rapidly or undergoes polarity reversal, the discharge risk of sharp tips cannot be assessed solely on the basis of the steady-state corona inception threshold under unipolar excitation. The present work provides an experimental basis for understanding corona mechanisms at grounded sharp conductors and for evaluating discharge risk under thunderstorm conditions.