Research On Active Suppression Method Of Secondary Arc Current Of Half-wavelength AC Transmission

The distribution of major energy bases and load centres is mismatched in the world.Under the background of the global energy interconnection,it is a hot topic of great concern to develop the Arctic wind energy and equatorial solar energy and to realize the long-distance power transmission over countries and continents.As a result,it is necessary to develop the transmission technology with ultra-long distance,large capacity and high reliability.Half-wavelength AC transmission(HWACT)is a three phase AC transmission technology that shows its potential to all the demands above.However,the fault recovery efficiency of HWACT system is affected by secondary arc current.There are some drawbacks in the existing research on this problem.This thesis mainly studies the active suppression method of HWACT secondary arc current.Firstly,a brief introduction of HWACT in the aspect of principle is given.The steady state characteristics of the HWACT system are verified by theoretical analysis and simulation calculation.Then,the generation of secondary arc current is introduced.The distribution characteristics of it along the HWACT line are summarized,which is in saddle-shaped with two peaks near to the middle point of the HWACT line.The amplitude of secondary arc current of HWACT is bigger than that of normal lines.After that,the suppression methods of conventional transmission lines are analysed and their drawbacks are shown when applied in HWACT system.In addition,the active suppression method of secondary arc current based on Modular Multi-level Converter(MMC)is proposed.The main circuit parameters of MMC are selected and the control strategy is designed.The rated capacity of MMC is reduced by switching passive components,which improves the economy without discounting the performance of the suppression method.Simulations are carried out in PSCAD/EMTDC which verifies the feasibility of the active suppression method under different operating conditions.The method proposed is compared with another two schemes.The results turn out that the active suppression method possesses good adaptability and shows better performance on the secondary arc current.