A DC Line Protection Scheme Based on Improved Longitudinal Impedance Method

In order to improve the quickness and reliability of longitudinal impedance protection for HVDC lines in hybrid cascaded HVDC systems, a novel longitudinal impedance protection strategy for HVDC lines based on improved hausdorff algorithm was proposed. When the fault occurs in different locations of the ±800kV hybrid cascade DC transmission system, the measured electrical volume of the protection installation site presents a certain difference. On this basis, in order to improve the rapidity of protection, with the help of fractal theory, the sampling window is improved to make the window self-adaptive, so as to improve the rapidity of protection. Then, the required electrical volume is processed by the hausdorff algorithm, and the problem that the longitudinal impedance protection requires high information synchronization is overcome by the combination of the two, so as to ensure the reliability of protection. At the same time, PSCAD/EMTDC hybrid cascaded DC transmission model is established, and the proposed protection strategy is verified by MATLAB. The simulation results show that the proposed protection scheme can operate quickly and reliably within 5ms by improving the adaptive window, with high reliability and good rapidity. Have certain anti-interference and anti-abnormal data ability; Under different working conditions, it can quickly identify faults outside the area and operate reliably.