Modified amplitude ratio of positive-sequence current based pilot protection for distribution networks with GFM-DG

The integration of grid-forming distributed generators (GFM-DGs) transforms radial, single-source distribution networks into complex networks supplied from multiple terminals. Unlike grid-following control, which exhibits controlled-current-source characteristics, grid-forming control exhibits controlled-voltage-source characteristics during faults. This behavioral difference alters fault signatures and challenges conventional protection schemes. Accordingly, this study characterizes variations in positive-sequence current magnitudes at both ends of a protected section for GFM-DGs connected at different positions relative to the section. A correction factor is introduced to compensate the current-magnitude ratio and eliminate the influence of T-connected GFM-DGs. A fault-detection criterion is then formulated based on the ratio of positive-sequence current magnitudes measured at the two ends of the protected section. Simulation results demonstrate that the proposed method remains effective across different fault types, fault locations, and fault-resistance levels, with strong tolerance to high fault resistance. These results indicate that the method provides robust and reliable fault detection across diverse fault conditions.