Wave characteristic impedance protection for transmission lines

In view of the existing transmission line protection, such as pilot differential protection and distance protection, which are affected by capacitance current to ground, current transformer saturation and transition resistance, a new principle of transmission line protection based on wave characteristic impedance was proposed. Firstly, based on the equations of transmission line, the voltage and currents of each point on the line were decomposed into forward traveling wave and backward traveling wave, and the characteristics of forward traveling wave and backward traveling wave of voltage and current at two ends were analyzed. Then, based on the decay characteristics of voltage fault component at the beginning of line and differential current between two ends of the line, the forward wave characteristic impedance and the backward wave characteristic impedance were constructed. Difference of these two impedances under internal faults and external faults are analyzed, and a wave characteristic impedance-based protection was proposed. The simulation results show that the proposed protection can accurately identify the internal and external faults of the transmission lines, has clear selectivity, and can protect the whole line without being affected by the transition resistance of short circuit point. © 2020, Harbin University of Science and Technology Publication. All right reserved.