Effects of the rainfall rate on corona onset voltage gradient of bundled conductors in alternating current transmission lines in high-altitude areas

Abstract

Corona onset voltage gradient (COG) of bundled conductors is an important factor to be considered when designing extra-high voltage (EHV) and ultra-high voltage (UHV) transmission lines. For alternating current (AC) transmission lines, the electromagnetic environment degrades and the energy loss is greater on rainy days, which becomes more obvious with increasing altitude, therefore, it is particularly important to investigate corona onset characteristics of bundled conductors under rainy conditions in high-altitude areas. Based on an UHV corona cage established in Qinghai Province, China at an altitude of 2200 m, corona onset characteristics of nine types of bundled conductors generally used in EHV and UHV AC transmission lines were measured at a rainfall rate of up to 15 mm/h. Moreover, COG was obtained by using the tangent method. Changes in COG with rainfall intensity and corona characteristics with structural parameters of conductors at the saturated rainfall rate were investigated. Finally, considering sub-conductor radius, the number of sub-conductors, and rainfall rate, an empirical prediction equation for COG of bundled conductors with 4, 6 and 8 sub-conductors and cross-sectional areas of 400, 500, 630, and 720 mm2 was proposed, which could provide a reference for the design of overhead transmission lines in high-altitude areas.