The differential protection of HVDC transmission lines is easily influenced during fault transient process

which limits its speed of action. Thus

research on a novel pilot protection scheme of better performance is needed. The traveling wave spreading processes in internal and external faults are analyzed. For the external fault

the forward traveling wave on the faulty side and the backward traveling wave on the non-faulty side are the same traveling wave with a strong similarity in waveform. In the case of the internal fault

the forward traveling wave on one side is different from the backward traveling wave on the other with a weak similarity in waveform. According to this feature

a novel high-speed pilot protection scheme based on the waveform correlation analysis of traveling wave is proposed. Simulation results show that the protection scheme proposed is able to rapidly distinguish the internal fault from the external fault

accurately detect the high impedance fault

and correctly identify the faulty pole. The proposed protection is suitable for HVDC systems of different voltage levels and has no high requirements on data synchronization.