A New Principle of Pilot Protection based on the Ratio of Fault Negative-Sequence Current and the Difference of THDi

In view of the problem that a high proportion of Distributed Generation (DG) connected to the power distribution network makes traditional stage-based current protection inapplicable, a new principle of pilot protection based on the difference between the faulty negative-sequence current ratio and the current THDi is proposed. First, the characteristics of the fault current on the active distribution network side and the DG side are analysed, taking into account the characteristics of negative-sequence current suppression and the distortion of fault current of distributed photovoltaic. Second, protection criteria based on the faulty negative-sequence current ratio are proposed for asymmetric faults, and protection criteria based on the difference between the THDi of the fault current are proposed for symmetry faults. Finally, the effectiveness and reliability of this protection scheme is verified by building a pscad model. This protection scheme only requires transient information about the fault current at both ends and does not require voltage information, which can effectively reduce the difficulty of on-site construction.