Study on overvoltage in ±200 kV triple-circuit DC transmission lines on the same tower for an AC-to-DC transmission project

Converting double-circuit AC transmission lines on the same tower to triple-circuit DC transmission lines can significantly enhance transmission capacity without requiring large-scale additional investments or consuming transmission corridor resources. Focusing on the insulation coordination design of triple-circuit DC lines on the same tower， this paper examines the ±200 kV Yangzhou-Zhenjiang AC-to-DC transmission project， the first of its kind in China. Six DC pole line layout schemes are analyzed to compare the distribution characteristics and maximum overvoltage along the DC lines， with results further compared to single-circuit DC line configurations. Additionally， the factors influencing overvoltage levels in triple-circuit DC lines on the same tower are explored. The findings indicate that the overvoltage distribution characteristics along the line are similar across different layout schemes for triple-circuit lines， and the overvoltage levels for triple-circuit lines on the same tower are slightly lower than those of single-circuit lines. Key influencing factors include the DC system’s transmission power， the main capacitance of DC filters， and soil resistivity. These results have provided a technical foundation for the design and construction of the Yangzhou-Zhenjiang AC-to-DC transmission project.