When corona or glow discharge occurs before the breakdown in air gap

air humidity may affect the AC breakdown voltage. However

the parameters ranges of the influenced electrode structure are not clear. In order to further reveal the influence of air humidity on the breakdown characteristics of short gaps under non-uniform AC electric fields

the AC breakdown tests were carried out with the interelectrode gap distance of 1～5 cm and the high voltage electrode radius of 0.1～2 cm. The results show that

within the given parameters of the electrode structure when the electrode radius is larger than 0.5 cm

the humidity has a negligible effect on the breakdown voltage. When the electrode radius is less than0.5 cm

the humidity will affect the breakdown voltage

especially under longer gap distances. When the electrode radius is 0.3 cm

the influence of the humidity is the most significant. Combined with the analyses of the hybrid breakdown criterion

the streamer breakdown criterion is still effective when the geometric structure parameter is larger than the critical value

but the breakdown field formula should be corrected in partial regions with the humidity being considered. The results can provide a reference for the insulating design of non-uniform air-insulated gaps.