| Due to the inverse distribution of energy storage and load demand in China, the fundamental theoretical breakthrough in 1000 km-3000 km power transmission technology is desired. The distance of international power transmission in plan also may reach or even exceed 3000 km. As a special kind of long-distance transmission, half-wavelength alternating current transmission (HWACT) has nowadays drawn more attention in ultra-distance point-to-point transmission mode, thanks to its unique advantages in both economical and technological aspects. Therefore, the explorative research on some key issues of the UHV HWACT has broad academic significance and important practical value.Based on the current research status of HWACT, this dissertation did explorative research on some key issues of the UHV HWACT in order to establish the theoretical foundation for the future development of HWACT. In thins dissertation, a detailed analysis with regards to the key technical issues of the UHV HWACT is given, including voltage and power transmission characteristics, system stability analysis of half-wavelength lines, power frequency and the fault-caused overvoltages, the secondary arc and its suppression, etc.The voltage and power transmission characteristics of the half-wavelength lines are different from those of normal short lines. By introducing the equivalent impedance of the system and power factor, this dissertation deduced the formula of voltage maximum and its position. According to the transmission power equation of the lossless long lines, the power transmission characteristics of the natural and tuning half-wavelength lines are analyzed, indicating that capacitive based tuning network rendering better power transmission ability.The angle stability of half-wavelength line was influenced by line length, tuning network type, fault type, fault duration and etc. By establishing the UHV duplex machine system simulation model, angle stabilities of natural and tuning half-wavelength lines were analyzed with different influencing factors such as man-made tuning network, line length and fault types. Based on the quantitative comparison of parameters such as fault duration, generator-swing trajectories amplitude and duration, voltage vibration range, the influence mechanism of angle stability of half-wavelength line was revealed.A simulation model for analyzing transient process of the half-wavelength transmission line was built with a view to calculate the power frequency overvoltages and the fault-caused overvoltages along the natural and tuning half-wavelength lines. Taking the single phase earth fault as an example, the fault-caused overvoltage along the lines of faulty phase and healthy phase was analyzed. The impacts of transmission capacity and man-made tuning network on the overvoltages were also investigated. An optimized scheme of the metal oxide arresters (MOAs) arrangement was proposed in order to limit the value of the fault-caused overvoltages to 1.60 p.u.Based on a simplified coupling model, formulations to describe the secondary arc current and the recovery voltage were deduced to calculate the distribution characteristics of the secondary arc current in different fault location. The impacts of transmission power, man-made tuning network, line length on the secondary arc current and recovery voltage were investigated. An optimized scheme of high speed grounding switch (HSGS) arrangement was proposed as to shorten the arc time of secondary arc. Based on black-box model of arc, an optimal time sequence for single phase auto-reclosing scheme (SPAR) specifically with UHV HWACT line was put forward.The research achievements in the dissertation have further developed the fundamental theory and key technologies encountered in HWACT, which provided important reference value for the development and engineering application of UHV HWACT.
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