Hybrid HVDC transmission has become a research hotspot in order to give full play to their advantages. In this paper, the protection principle of hybrid bipolar HVDC transmission lines consisting of traditional HVDC transmission and flexible HVDC transmission is studied. Firstly, the paper analyzes the additional state of the DC line when a fault happens on hybrid bipolar HVDC transmission line. Based on the analysis, the protection principle of distinguishing the fault from the internal and external using the transient power component is proposed, and the transient power component is extracted by the secondary B-spline wavelet transform. Secondly, this paper integrates the transient power of the positive pole rectifier side and the transient power of the negative pole rectifier side respectively, and constructs the energy function to perform the fault pole selection. Finally, using PSCAD to build a simulation model, using MATLAB to simulate the algorithm validation, a large number of simulation results verify the correctness of the proposed protection principle, and can identify fault pole.
