Corona onset criterion and surface electric field intensity characterized by space charge density

The accurate evaluation of corona onset criterion in air gap under high voltage has important theoretical and practical significance, but it is calculated and measured inaccurately at present because of the distortion caused by space charge. In this study, space charge density is measured by contactless acoustic device and it can directly determine the corona onset voltage and surface electrical field. The direct detection of space charge can eliminate the distortion of charge when other parameters are used to measure corona onset criterion. The experimental onset voltage in this work are compared with that calculated by Peek's formula, corona current and photon number. Results demonstrate the applicability and accuracy of this method. In the other hand, maximum space charge ratio is adopted to analyze the change rule of surface electrical field. It is found that the surface field strength is not constant after corona occurs and should be lower than the onset electrical field. This study provides a feasible approach to further study the effect of space charge on corona onset criterion in air gap.