Switching Strategy And Fault Analysis Of Earth Metal Loop For Hybrid Three-terminal HVDC Transmission

Multi-terminal hybrid flexible DC power transmission is an important development direction of DC power transmission in China. Firstly, the structure of the threeterminal HVDC system, the structure of the three-terminal earth loop and the metal loop are modeled. Then the conversion steps and differences between conventional DC and flexible DC earth/metal loop are analyzed. Finally, this paper studies the possible ground faults and fault characteristics in the threeterminal earth metal return line conversion process, points out the influence of the metal return line grounding fault on the three-terminal hybrid HVDC system, and gives the corresponding protection configuration according to the fault types.