The Evolution Study of Positive Corona in Atmospheric Air Based on the Combination of Light Radiation and Discharge Current

Clarifying the transition process between various corona stages is helpful to ensure a stable corona application and prevent destructive failure of power equipment. This article investigated the current waveform evolution of positive corona for a needle-plate configuration under a slow ramp voltage, and the light radiation was detected synchronously by the silicon photomultiplier (SiPM). Positive corona before spark discharge has four stages with increasing applied voltage, i.e., burst pulse stage, Hermstein’s glow stage, streamer stage, and breakdown streamer stage. The current pulse magnitude (CPM) representing the discharge intensity and the SiPM magnitude representing the light radiation intensity exhibit different relationships at these stages. In addition, the current waveforms exhibit distinctive shapes at four stages. To explain the evolution of the current waveform, a hydrodynamic simulation model considering photoionization in a 2-D axisymmetric geometry is proposed. According to the simulation results, the streamer onset criterion of Meek is fulfilled when the local electric field strength is high enough to attract secondary avalanches into the area of the initial electron avalanches. As the streamer approaches the cathode, the current spike at the breakdown streamer stage is caused by the surge of the electron multiplication factor rather than the secondary electron emission from the cathode.