Study on Electrical Transient Protection for ±800kV UHVDC Transmission Lines

The physical boundary of a high voltage direct current (HVDC) transmission line consists of smoothing reactor and DC filter. It has the stop-band characteristic to the high-frequency transient voltage components. The high-frequency voltage signal from the external of DC transmission lines will be weakened when it travels through the smoothing reactor and DC filter. Its power will also be much smaller. The wavelet energy of the high-frequency transient voltage can be gotten through wavelet transformation. The identification criterion of internal and external fault is based on the conspicuous difference of the wavelet energy of high-frequency transient voltage at the point of relay installation. The wavelet transformation modulus maximum of the fault transient voltage is used as the criterion of starting. The fault line is selected based on the polarity wave of the two lines. The simulation is performed considering commutation failure, and the fault distance to the single-ended electrical transient protection. The simulation results show that the protection has absolute selectivity, which can steadily and effectively protect the whole lines.