The half-bridge modular multi-level converter does not have the DC fault blocking capability and the high transient failure rate of the scheme of voltage source converter based high voltage direct current(VSC-HVDC)transmission overhead line. This paper proposes a three-capacitor clamping double sub-module(TCDSM)topology. Compared with the existing clamping double sub-module

the topology improves the isolated current fault isolation capability of the DC-side short-circuit based on the clamping double sub-module VSC-HVDC transmission. The working mechanism and performance analysis of TCDSM topology is introduced in detail

and a new hybrid arm converter scheme is proposed. Compared with the hybrid arm system

which is composed of the clamping double sub-module and the half-bridge module

the cost of new operation is lower than that of the hybrid arm device without sacrificing the blocking capability

optimizing the overall converter station construction costs. Finally

the feasibility of the topology and the new hybrid arm is verified by simulation and experiment.