A Novel Directional Pilot Protection for Flexible DC Distribution Grid

The existing directional pilot protection (DPP) is susceptible to the line distributed capacitance and the fault resistance, and mostly rely on the current limiting reactance (CLR) at the line ends. To solve the above problems, the line-mode fault component power (LFCP) based DPP is proposed for flexible DC distribution grid (FDCDG). First, the characters of LFCP are discussed under different faults. The theoretical analysis show that the polarity of the LFCP under internal fault is same, while the polarity of the LFCP is opposite under external fault. Then, the LFCP is built as the directional criterion, and the corresponding protection scheme is constructed. The electromagnetic transient simulations of the PSCAD/EMTDC verify that the proposed DPP is less affected by the noise, and has low requirement on the sampling rate, strong engineering applicability.