The induced overvoltage between UHV AC and DC transmission lines built on the same tower under fault conditions

Rapid increase of the transmission capacity and environmental limit of the power transmission passage have indispensably promoted development of the AC/DC hybrid transmission lines on the same tower, especially for UHV systems being established in China. Unfortunately, severe electromagnetic coupling effects will inevitably exist between the UHV AC and DC transmission lines built on the same tower. The generating mechanisms, as well as the computational methodology, of both the electrostatic and electromagnetic coupling effects within the hybrid transmission lines are elucidated in the paper, then an equivalent circuitry model is established as to analyze the induced overvoltage within the hybrid transmission lines under different fault conditions. Further, the impacts on the induced overvoltage from key influential factors, such as the grounding fault resistance, the collocation and layout of DC filters and smoothing reactors, are accounted for in details, and the overvoltage scenario along the healthy lines is drawn with regard to various fault conditions. Specifically, phase-mode transform method is adopted to theoretically analyze the effect of transposition mode of the UHV AC transmission line as how to reduce the induced overvoltage within the hybrid transmission lines. The proposed method and analyzed results present reliable reference for realizing optimal design of the UHV AC/DC hybrid transmission lines.