Influence of conductor coating and bundling on corona phenomenon of hybrid AC/DC transmission lines

This paper presents theoretical and experimental investigations of the factors affecting corona phenomenon on hybrid AC/DC transmission lines using a single-phase AC (50 Hz)/single-pole DC reduced-scale model. A field computation program is used to model both an AC 132-kW double-circuit transmission line and an analog hybrid line. The results reveal that the corona inception voltage of DC conductors is much higher than that of AC conductors, where it augments with increasing number of bundles, coating thickness and/or permittivity. Conductor coating and/or bundling causes a drastic reduction in both audible- and radio-noise profiles, but there is no effect of bundle orientation. The trends of the experimental results are in agreement with the computed corona inception voltage, number of streamers and electric field. Increasing the number of bundles and/or DC voltage reduces the AC corona current, and so does the number of streamers. Both the interspacing between AC and DC conductors, and the relative amplitude of applied voltages determine the variation of AC corona current. Conductor coating gives an economical solution to increase the corona inception voltage, and reduces the number of streamers at the conductor surface. For thinner coatings, the AC corona current is unchanged while the DC corona current increases.