Second- and third-zone performance assessment of a symmetrical component based improved fault impedance estimation method

The performance assessment of a symmetrical component based fault impedance estimation method that has previously been proposed by the authors is discussed in this paper. A brief review of the proposed method is given. The personal computer based Alternative Transient Program was used in these performance assessment studies. Voltage and current signals for various fault conditions were generated by simulating different types of fault on a selected transmission line of a sample power system. These signals were processed, sampled, and used in the proposed method. The apparent impedance of the protected transmission line from the relay location up to the fault point was calculated using the proposed method. These impedance estimates were inserted in R − X plane characteristics to determine the suitability of the proposed method for digital distance protection of the second and third zones. The results of these performance assessment studies are presented and discussed in the paper.