Experiments and analysis of corona inception voltage under combined AC-DC voltages at various air pressure and humidity in rod to plane electrodes

As the effect of climate plays a significant role in corona discharge under combined voltages, the variation of corona inception voltage with different air pressure and humidities is studied. An experimental platform, based on a rod-to-plane electrode, is constructed with adjustable air pressure from 0.06 MPa to 0.10 MPa and with a relative humidity (RH) from 20% to 90%. The variation of ultraviolet (UV) photon count and corona inception voltage is obtained at various climate conditions under different applied voltages: the single AC, single DC, and combined AC-DC. It turns out that all the corona inception voltages decline with the drop of air pressure and the rise of humidity under different applied voltages. The influence between different voltages primarily relies on space charge, as more AC components make it easier to accumulate positive ions. The existence of AC makes ions move forward and backward while the existence of DC dominates the polarity of corona and general drift directions. At last the fitting formula of hybrid corona inception voltage combining air pressure and relative humidity is given.