A pilot protection on Hybrid DC line based on correlation coefficient

In order to ensure the safe operation of the hybrid double-ended HVDC transmission system, the current similarity between the two ends of the hybrid double-ended DC transmission line is analyzed in this paper.By analyzing the fault characteristics，it is found that the fault current on both-end lines when internal fault occurs is no obvious linear relationship,whereras the fault current on both-end lines when external fault occurs is obvious linear relationship. According to the difference of current fault characteristics on the double-end lines when internal or fault occurs, a pilot protection method for hybrid DC transmission lines based on correlation coefficient is proposed in this paper. The simulation model of LCC-MMC hybrid double-ended DC transmission line was built by PSCAD, which is used to output the fault data under different conditions. And the fault data processed with MATLAB to carry out the algorithm simulation.The simulation results verify the correctness of the proposed protection method. In the practical application, the proposed method does not need the fault data on both ends to be strictly synchronized,and it can identify the fault quickly and reliably with strong practicability.