Protection of HVDC transmission lines based on wavelet transformation and analysis of energy spectrum

To remedy the difficulty in distinguishing between internal faults and external faults quickly in HVDC system, the difficulty in distinguishing between the fault pole and sound pole and the malfunction while lightning interference, a set of voltage traveling wave protection scheme is proposed. First, we propose the voltage travelling wave polarity comparison protection method based on the wavelet transformation, in which we can distinguish between internal faults and external faults quickly. Second, using the transient voltage energy distribution character in different frequency range, we can distinguish the faults and lightning interference. Using the same method, we can distinguish the fault and sound pole in bipolar system. By testing this scheme in MATLAB/Simulink, we have proved that this scheme can function reliably. It is not affected by fault type and location. The fault impedance has little impact on the result. Therefore, this scheme is fast, sensitive and reliable, meeting the need in HVDC protection.