Research on influence factors of corona onset characteristics of AC grading rings based on three‐dimensional calculation physical model

In order to obtain the influence laws and mechanisms of size parameters (ring diameter and pipe diameter) of the grading ring and environmental parameters (atmospheric pressure, temperature, and humidity) on corona onset characteristics of a grading ring, a three‐dimensional (3‐D) calculation physical model of corona onset considering the influence of size parameters of the grading ring and environmental parameters is established by proposing an area factor of a photon absorption function suitable for the grading ring. Combined with the thickness of ionised layer and the effective ionisation coefficient, the influence mechanisms of size parameters of the grading ring and environmental parameters on corona onset characteristics are given. The calculation results show that with the increase of the pipe diameter and ring diameter, the corona onset voltage increases gradually and the corona onset field intensity decreases gradually. The increase of the effective ionisation coefficient leads to the expansion of ionisation region, which leads to the decrease of corona onset voltage with the decrease of atmospheric pressure and the increase of temperature. The enhancement of capacity for collisional ionisation in the region with the high field intensity leads to the decrease of corona onset voltage with the increase of humidity.