Influence of UHV DC Transmission Line on Overvoltage of AC Transmission Lines Built on the Same Tower

With further development of the electric power industry in China,the HVDC line,thanks to its advantages for long distance transmission,has become a promising trend in the UHV transmission technology.Due to shortage of power transmission corridor shortage in some regions,adoption of the AC/DC hybrid transmission lines on the same tower becomes inevitable.When DC/AC transmission lines are erected on the same steel tower,strong electromagnetic coupling will be generated between conductors and a series of problems arise from the interactions between AC/DC lines,among which the effect of DC ground faults on AC lines is the main concern in this paper.According to the parameters of Ximeng-Shanghai AC/DC hybrid transmission project under planning,in the paper,the detailed simulating model of DC converter station and hybrid transmission line with double circuits AC transmission lines and DC transmission line are presented,and overvoltage caused by the DC ground fault on DC sound pole and adjacent AC lines are simulated,and several influencing factors such as different DC fault types,different operation modes,hybrid lengths and fault positions,are considered.The simulation results show that the overvoltage levels on AC lines generated by DC line faults are lower than the permissible values of AC insulation coordination margin.The fundamental frequency secondary arc current will be generated through AC/ DC coupling during DC pole-ground fault,which will interfere with the clearing of DC fault.Sev eral factors of secondary arc current such as AC transposition modes,fault position and AC conductor disposal schemes are discussed in the paper,and finally some restricting methods are presented for the design.