Research on an Improved Protection Principle Based on Differential Voltage Traveling Wave for VSC-HVDC Transmission Lines

When a short-circuit fault occurs in the VSC-HVDC transmission system, the DC-side current increases and the voltage decreases rapidly, which can pose a serious threat to the normal operation of the system. In order to meet the requirements for speed, selectivity, sensitivity, and reliability of the VSC-HVDC transmission system, the propagating characteristics of voltage traveling wave after a fault occurs in the VSC-HVDC transmission line are analyzed, and then an improved protection principle based on the differential voltage traveling wave considering the frequency-dependent line parameters is proposed. A data out-of-sync detection method only using the electrical quantities on both ends of the line is studied to prevent the protection from mal-operating when there is something wrong with the synchronization clocks. The causes of operation delay are further analyzed and the delay time is estimated for determining the possible application of the protection scheme. Finally, correctness of the protection principle and relevant algorithms are verified by the combination of MATLAB-based protection program and PSCAD-based simulations.