Experimental Investigation of Discharge Characteristics of a Sphere-plane Long Air Gap Under Switching Impulse Voltage

Previously, the research about the discharge characteristics of long air gaps mainly focused on the gaps with severely inhomogeneous electric fields such as rod-plane, and rod-rod, where the electrode size is generally small. The sphere-plane air gap exists in the valve hall of the converter station in ultra-high-voltage (UHV) direct-current power transmission projects, and fewer studies have been conducted on its discharge characteristics. In this paper, a sphere-plane long air gap discharge experimental platform containing a current measurement device and a high-speed camera is built. The breakdown characteristics of sphere-plane long air gaps with different spherical electrodes and different gap distances are studied by applying positive switching impulse, and the physical parameters of different discharge stages of 0.3 m spherical electrode are obtained by measuring the discharge current from the high voltage electrode and recoding the optical images. The experimental results obtained the breakdown voltage variation patterns of 0.05 m, 0.1 m, 0 15 m, 0 2 m, and 0.3 m spherical electrodes under 1 m to 2 m gap distance. Also, the discharge parameters of each stage of the streamer-leader discharge process of the 0.3 m-spherical-electrode under 1 m and 1.5 m gap are observed. The resultant observations show that the breakdown voltage gradually increases and tends to saturate as the radius and distance of the electrode increase; the leader inception time, leader inception voltage, and leader velocity increase with increasing distance.