A Three-Zone Distance Protection Scheme Capable to Cope With the Impact of UPFC

To improve the power transfer capability and reliability of the power grid, the unified power flow controller (UPFC) project has been put into operation in the western Nanjing power grid. Based on the practical project, the influence of UPFC on the distance protection is analyzed. To cope with that, the novel three-zone distance protection scheme is put forward. The zone 2 and zone 3 of the novel three-zone distance protection scheme are the same with those of conventional distance protection; however, the novel distance protection zone 1 is based on the parameter model of transmission line. According to the average value and fluctuation degree of the fault distance calculation results, the proposed distance protection zone 1 can effectively distinguish between the internal faults and external faults. More importantly, the proposed distance protection zone 1 can realize effective cooperation with the conventional distance protection zone 2 and zone 3, to construct a complete three-zone distance protection scheme and guarantee the correct operation of the novel three-zone distance protection scheme. The simulation cases in the PSCAD/EMTDC software environment verifies that the proposed three-zone distance protection has excellent performance, and would not be affected by the operational mode and control parameters of UPFC.