500-kV EHV Bundle Conductors´ Corona Onset Voltage Calculation and Analysis in Corona Cage at Different Altitudes

In order to research an altitude´s effect on corona onset voltage of bundle conductors in a corona cage, a calculation model was established, and corresponding test proceeded. The charge simulation method was adopted to calculate space electric-ήeld strength. According to self-sustained discharge criterion in a severe nonuniform electric ήeld, and variation of altitude, the corona onset voltage calculation model of bundle conductors in a corona cage was established. The corona onset voltages of bundle conductors, which were used in the 500-kV extremely high voltage transmission line, were tested at different altitude locations, as Wuhan 19 m, Xining 2261 m, Golmud 2829 m, and Nachitai 3800 m. Corona onset voltages of 4 × LGJ - 0400/5 and 4 × LGJ - 300/25 were obtained. The corona onset voltage curves at different altitude, bundle spacing, and bundle numbers were obtained. The analysis shows that the model can be used to provide accurate values of corona onset voltage for bundled stranded conductors in the corona cage at various altitudes. With bundle spacing from 350 to 500 mm, the corona onset voltage decreases as bundle spacing increases, and the onset voltage increases as the bundle number increases. As altitude increases every 1000 m, the corona onset voltage of bundle conductors decreases by about 8.5%.