Modified VMD Algorithm based Fault Location Method for Overhead-Cable Hybrid Transmission Line in MTDC System

Fault location based on travelling wave (TW) of multi-terminal DC (MTDC) transmission system is playing an important role in safe and stable operation of power system. The existence of wave impedance discontinuities in overhead-cable hybrid transmission lines (OCHTLs) leads to abrupt changes in TW velocity., which the traditional TW based fault location method is not adaptable. This paper proposes a novel fault location method for OCHTLs., which could increase the fault ranging accuracy. Firstly., typical OCHTL equivalent model is established and the propagation characteristics of the fault voltage TW (VTW) of OCHTLs is studied. On this basis., Variational Mode Decomposition (VMD)-Teager energy operator (TEO) algorithm is used for extracting the arrival time of voltage TW head-wave. Aiming at the problem of modal aliasing during the parameter selection of VMD, K- L divergence is utilized to optimize the modal number and penalty factor of the VMD algorithm. Moreover., by analyzing the attenuation characteristics of zero-mode and line-mode voltage., the relationship between velocity and arrival time of line-mode voltage TW is used to construct the faulty segment criterion. Subsequently., a higher precision fault location algorithm based on two-terminal information of fault segment is proposed. Finally., a MTDC with OCTHLs is built in PSCAD to verify the robustness and correctness of proposed algorithm.