A computational discharge model for sphere-plane long air gap under switching impulse voltage

There are lots of sphere-plane air gaps in valve halls in extra-high-voltage and ultra-high-voltage converter stations. Accurate prediction for discharge characteristics of sphere-plane gaps is of great significance for the selection of shielding structure and determining the dielectric strength of the valve hall. In this paper, based on the physical process of corona inception and continuous leader inception, a computational model for calculating the discharge voltage of a sphere-plane air gap under positive switching impulse voltage is proposed, and the leader characteristics and discharge voltage are analyzed. Then, the switching impulse discharge test of the sphere-plane gap with 0.15, 2, and 0.3 m radius spherical electrodes is carried out to verify the correctness of the model. The results show that the discharge voltage calculated by the proposed method is consistent with the test results, and the error is within 7.3%. The leader inception voltage and inception time increase with the increasing spherical electrode radius at the same gap distance, and an identical spherical electrode require higher leader inception voltage and faster leader inception time with the increasing gap distance.

Automated summary

There are many sphere-plane air gaps in valve halls of extra-high-voltage and ultra-high-voltage converter stations. Accurate prediction of discharge characteristics in these gaps is important for selecting shielding structure and determining dielectric strength. This paper proposes a computational model based on corona inception and continuous leader inception processes to calculate the discharge voltage of a sphere-plane air gap under positive switching impulse voltage. The model's accuracy is verified through experiments, showing a maximum error of 7.3%. The results also indicate that the leader inception voltage and time increase with larger spherical electrode radius at the same gap distance, and larger gaps require higher leader inception voltage and faster leader inception time for identical spherical electrodes.