Breakdown conditions of short air-insulated gaps under alternating non-uniform electric fields

The breakdown conditions of short air-insulated gaps under alternating non-uniform electric fields are investigated for providing an accurate prediction of the breakdown voltages of commonly used electrode systems. The breakdown voltages with the tip radius of the highly stressed electrode varying between 0.1 cm and 2 cm and the gap distance ranging from 1 cm to 5 cm were experimentally investigated, and the breakdown electric field distributions in inter-electrode gaps were analyzed by a finite element method. An abnormal phenomenon was observed that the breakdown voltage increased in a highly non-uniform electric field with the same gap distance. For different electrode arrangements, the breakdown conditions could not be characterized by the relationship between the maximum breakdown electric field at the electrode tip and the field non-uniform coefficient. Therefore, a combined breakdown criterion was proposed by introducing a geometrical parameter of the electrode system. The breakdown conditions can be, respectively, evaluated by the streamer inception criterion and a fitting formula when the value of the geometric parameter is on opposite sides of a critical value. Published by AIP Publishing.