Drift-diffusion model of corona discharge in coaxial geometry due to negative lightning impulse voltage

Abstract

Corona discharge at atmospheric pressure in cylindrical geometry is simulated numerically for negative lightning voltage impulse. The simulation is performed by solving the drift-diffusion-reaction equations for electrons, positive and negative ions. Spatial dependence and time evolution of the concentration of charged particles and created space electric field are used for detailed theoretical analysis of corona discharge based on the values of the transport and reaction gaseous coefficients. This exact drift-diffusion model enables clear physical picture of the corona discharge dynamics. It is used for the determination of the charge-voltage curves necessary for taking into account the corona effects in transient overvoltage calculation on transmission lines. In contrary to the previous engineering corona models, it is shown that the corona charge continues to increase although the input voltage pulse decreases after reaching its maximum value. This behavior is confirmed by measurements in a few experimental studies. Secondly, it has been shown that according to this model there are no positive streamers formation departing from central electrode or wire during decreasing edge of the input voltage pulse. The total charge simply commences to decrease when the negative ions neutralize themselves on the central electrode or wire of positive polarity. A sharp peak of corona current is observed immediately after the beginning of the intense ionization. The drift-diffusion model could also be used to check the validity of other common assumptions and predictions of previous engineering corona models.