Implementation of an adaptive data window technique in a distance relay

This paper describes the design, implementation and testing of a distance relay that uses an adaptive data window approach for calculating phasors and impedances from those phasors. The relay uses a detector to determine the inception of a fault. On the inception of a fault, a ten-sample window is used. The window size is progressively increased as new samples of voltages and currents become available until the window size becomes one period of the fundamental frequency. At each sampling instant, an appropriate technique is used for estimating the voltage and current phasors. This procedure reduces the transient response time of the relay and results in providing converged estimates of the impedance, and consequently trip decisions, in shorter times in most cases. Some results demonstrating the performance of the technique are included in the paper.