Improved relay algorithm for detection and classification of transmission line faults using signum function of instantaneous power

A novel algorithm on fault detection and classification employing instantaneous power using signum function was reported in 2014 [6]. However, the performance analysis was not exhaustive and the effect of the line load on the relay behavior was not reported. A detailed investigation has been carried out by the authors of this paper to study the effectiveness of the technique using instantaneous power flows and the relay algorithm has also been improved. The 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 of fault and fault resistance. Various fault resistance values ranging from 0.01 ohms to 1000 ohms have been taken for simulation. The study has been carried on two types of lines: a line between a source bus and a load bus and a line connected between two source buses. Results of the study are presented in this paper. The final outcome of the study is that the technique works successfully with low fault resistance values and low line loading but fails to detect fault with high resistance faults occurring on heavily loaded lines.