A Differential Protection Scheme for Hybrid Three-Terminal DC System

To enhance the rapidity, sensitivity, reliability and selectivity of differential protection for hybrid three-terminal HVDC lines and buses, a new differential protection scheme based on Hausdorff distance algorithm is proposed. When a fault occurs in ±800 kV mixed three-terminal DC line, the fault component values of line-mode current on both sides in T-zone are used as the fault direction discrimination basis of this scheme, and the scheme quantifies the difference of short-window data between the current waveforms of the first and last sides of the line, and uses the difference of current similarity between the first and last ends of the line to determine the internal faults and external faults, as well as the faults of unipolar and bipolar. The Hausdorff distance between T-zone sender (LCC side)'s current and two T-zone receiver (MMC side)'s total current is taken as the criterion of T-zone bus fault identification and protection. Then the hybrid three-terminal DC transmission system model is established by PSCAD and the protection method is verified by MATLAB. The simulation results show that the proposed scheme has strong ability to tolerate the transition resistance (500 Ω), and has the advantages of high reliability and speediness to ensure quick and reliable action within 3 ms. The communication time accuracy requirement on both sides of the line is low, and the scheme has a certain ability to resist noise and abnormal data. Under different working conditions, the fault area and the faults inside or outside the area can be quickly identified, and fault pole selection can be achieved. © 2021, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.