Influence of Humidity and Salinity on the Transformation of Positive Corona Discharge Modes in Rod–Plane Gap

In this article, the positive corona discharge in rod–plane gap was measured by noninductive resistance, photomultiplier, and ultraviolet imager. With the increase of applied voltage, different positive corona discharge modes are distinguished according to the difference of optical and electrical characteristics. The positive corona discharge develops from streamer discharge to glow discharge at low humidity, and the discharge of water molecules in air can be detected before streamer discharge when the relative humidity (RH) is higher than 80%. Humidity has little effect on the inception voltage of streamer discharge, while the inception voltage of glow discharge increases with the humidity. As for the positive corona discharge in salty air, the streamer discharge will never develop into the glow discharge but develops directly to a spark if the air humidity is somewhat high. The physical mechanism of positive streamer discharge and glow discharge is analyzed, and the evolution of space charge distribution during positive corona discharge is obtained by simulation. The glow discharge is characterized by the presence of negative ion sheath around the anode. The increase of humidity and salinity in air reduces the migration rate of negative ions, which is not conducive to the establishment of glow discharge.