Incremental Power Improves Relay Selectivity to Transmission Line Faults

摘要

A research work published in 2014 reported a novel relaying principle for protection of transmission lines using signum function of instantaneous power flows at the two ends of the line. Subsequently, a detailed study of this relaying principle to evaluate its selectivity (sensitivity to detect all internal faults and stability on external faults and no-fault condition) was carried out and results were reported in another paper. The present paper reports a considerable improvement in the relay selectivity by using signum function of incremental powers at the two ends of the line. This principle of fault detection and classification has been tested by simulating a 230 kV, 50 Hz five-bus system in PSCAD/EMTDC. The various parameters of the study include dc offset, line load, location and type of fault and fault resistance. Various fault resistance values ranging from 0.01 ohm (solid fault) to 1000 ohms have been taken for simulation. The study has been carried out on two types of lines: a line between a source bus and a load bus, and a line connected between two source buses, and for two line lengths, namely 100 km and 200 km. Results of this detailed study are presented in the paper. The final outcome of the study is that the relay is able to detect all internal faults with all fault resistance values and all line loads. However, it operates on some external faults near the load bus, that is, has some transient overreach, for the first type of line. This tendency of operating on external faults is also lower than that with the instantaneous power-based relay.