The Performance of Faulted Phase Selectors Used in Transmission Line Distance Applications

The reliable performance of faulted phase selectors to identify the faulted phase or phases and appropriately block or permit tripping is critical to the application of distance protection. The most difficult fault type to identify correctly is a two-phase-to-ground fault. Incorrect detection methods of this fault type has lead to undesired overreaching and/or tripping for remote two-phase-to-ground faults beyond the underreaching zone reach setting. It is also important to provide accurate fault location and record correct faulted phase information after the fault has cleared to correctly access the fault type characteristics. This paper analyzes the issues related to two-phase-to-ground faults and discusses several methods used for faulted phase identification and the advantages and disadvantages of each. It also shows how different phase selection methods may be used to complement each other to provide more reliable faulted phase identification.