Secondary arc current of ultra-high voltage transmission line with a mixed voltage of 1000/500 kV on a single tower

Among the ultra-high-voltage (UHV) grids in eastern China, the construction of multi-circuit transmission lines with mixed voltages on a single tower is a novel transmission technology that can significantly reduce line corridor coverage, maximise the use of tower height and significantly improve power transmission capacity per area. However, the electromagnetic interaction between lines is complicated and interferes with the secondary arc current. This study proposes a hybrid tower model that incorporates double-circuit transmission lines with alternating currents at 1000 and 500 kV. Its secondary arc current is investigated according to circuit analysis and EMTDC in consideration of the electromagnetic coupling effect, along with the influences of line length, compensation, phase sequence and transposition on the secondary arc current. Results show that a strong secondary arc current is generated for 1000 kV transmission lines in accordance with the UHV hybrid transmission project from Ximeng to Shanghai. This finding should be emphasised. Furthermore, the influence of quadruple-circuit line length on the secondary arc current depends on line voltage rating. Finally, this study presents several methods that may reduce the secondary arc current, such as transposing lines evenly and installing suitable neutral reactors.