Theoretical and experimental studies for spherical free-conducting particle behavior between non-parallel plane electrodes with ac voltages in air

This paper deals with free-conducting particle motion and particle-triggered breakdown in ac electric fields between non-parallel plane electrodes in atmospheric air. Spherical particle motion was investigated theoretically and experimentally under ac voltages with various frequencies, considering the effect of the electrical gradient force and the dependence of the Coulomb force magnitude on the distance between a particle and an electrode. The result shows that when the Coulomb force acting on a bouncing particle changes its direction periodically under ac voltage whose frequency is around commercial power frequency, the electrical gradient force can become effective in initiating particle motion toward decreasing electrode gap regions, causing the particle to trigger breakdown. Moreover, it was found that the direction in which a particle advances horizontally is greatly influenced by microdischarge occurrence when the particle bounces very near to the grounded electrode under high-frequency ac voltage, and that when a particle bounces on an electrode, particle-triggered breakdown voltage is decreased by the effect of microdischarge.