The Optimum Method for Determining the Corona Onset Voltage Gradient of Bundle Conductors on UHV AC Power Line

Abstract

The COG (Corona Onset Voltage Gradient) of bundle conductors, as an important parameter in the design of transmission lines, is related to the electromagnetic environment around the transmission lines. Therefore, it is important to accurately determine the COG. At present, there are several methods to determine the COG, the values of COG obtained by different methods are quite different, and the reasonableness of these methods is still not clear. In this paper, combined with the UHV corona cage set in Ping’an County, Xining city (elevation 2200 m), the corona characteristic measurement system and UV imager, the platform for measuring corona discharge characteristics of bundle conductors was built. For the 8 × LGJ-630 bundle conductors commonly used on UHV transmission lines, the change of corona discharge intensity was observed by UV imager. Then, the E (field intensity)–I (resistance current), the E–√P (square root of corona loss), E–PH (UV photon number), E–RI (radio interference), E–AN (audible noise) curves were measured. By using the tangent method, the experimental values of COG were obtained. Finally, the COG obtained by the five methods are analyzed and discussed, the COG values obtained by the E–I curve and E–√P curve are basically the same, with a deviation of about 1.5%, it has clear physical significance. While the deviation of the COG obtained by the E–PH, E–RI, and E–AN curves are about 10.4%, 29.9%, and 5.7%, respectively. And the optimal method proposed for determining the COG is E–I curve or E–√P curve.