Breakdown voltage of interelectrode gap between sphere-plane electrodes under ac voltage

The breakdown voltage in a small spacing under dc voltage application has been well described with the Paschen law. The present paper differs from the previous works in that we employ ac voltage. The electrode system employed is sphere-plane electrodes and the sphere and/or sphere electrodes are coated with an epoxy resin. The breakdown voltage of air gap of the Metal (M) - Air gap (G) - M, MG-Epoxy layer (I), IGI electrode systems is measured using the advantage of the excited particles from the previous breakdown under a fast rate-of rise of ac voltage. It is found that the breakdown voltage decreases by employing the epoxy coating on electrode in the whole range of the production Pd from 0.3 to 90 Pa·m. In the range of the small product Pd from 0.3 to 5 Pa·m, the possibility of breakdown becomes high when the polarity of brass electrode is negative for MGI electrode system. It is concluded that the epoxy coated electrode decreases the breakdown of air and enhances electric field for the small spacing.