In March 2021, the Shin-Shinano Substation of TEPCO Power Grid, Inc. was connected to the Hida Convertor Station of Chubu Electric Power Grid Co., Inc. by HVDC transmission system with an interconnection capacity of 900MW in order to increase the interconnection capacity between the eastern and the western areas in Japan. The 200kV HVDC overhead transmission lines have a pair of energized conductors and a return conductor. It has been investigated that TACSR (410mm² [AC410], 610mm² [AC610], 810mm² [AC810]) would be used as the return conductor. However, as the return conductor plays the role of a ground wire, the melting and breaking of TACSR strands due to lightning strike was concerned. Therefore, in this paper, numerical evaluations of melting and breaking characteristics of the return conductor strands were carried out supposing the return conductor was struck by DC arc discharge simulating lightning whose maximum current was 400kA. As a result, the number of breaking strands of AC610 was more than that of AC410 and AC810 because the diameter of strands of AC610 was smaller than that of AC410 and AC810. The remaining rate of cross-section area of strands of AC410 decreased more than AC610 and AC810 as DC arc current increased.