Optoelectronic measurements of prebreakdown current in an air gap

The prebreakdown current in the development of the corona streamer and the following leader stroke has been studied by use of an optoelectronic technique with high response characteristics. The prebreakdown currents flowing at both the high−potential and the earth−potential electrodes were simultaneously measured using rod electrodes arranged in parallel. The shape of the end face of each electrode was either needlelike or hemispherical. Except for the charging current, the observed current pulses flowing at the relatively positive electrode were always larger than those of the negative, despite the shape of the end face of the rod electrodes. From the results, it is suggested that the final spark path on the parallel electrode geometry will be dominantly decided by the development of the positive streamer or the positive leader corresponding to the current pulses observed at the relatively positive electrode.