Adaptive digital relay for comprehensive distance protection of traction overhead equipment

Protection of the overhead equipment (OHE) of single-phase 25 kV traction system is a special case of distance protection. In addition to the earth faults, wrong phase coupling faults take place on the OHE. In this paper, an adaptive protection scheme suitable for the single-phase 25 kV 50 Hz traction system used by the Indian and several other railways is presented. The proposed relay characteristic is a combination of two quadrilaterals in RL-plane, one for the earth faults and other for wrong-phase-coupling faults. The relay automatically selects the appropriate relaying algorithm on detecting the nature of the fault. Secondly, it automatically adjusts its reach to suit the prevailing feeding condition. Performance of the relay has been evaluated both by simulation on a personal computer and by real time implementation on a prototype. The prototype is designed around a 16-bit microprocessor, Intel 8086. For the evaluation proposed the fault data was generated using the simulation package EMTP/ATP developed by Salford University. The results of simulation and real-time test prove that the relay is capable of discriminating between internal faults, external faults and heavy loads, and detects internal faults in about a quarter cycle