Adaptive application of impedance estimation algorithms in distance relaying

The distance relay is one of the most important elements of EHV and UHV transmission line protection systems. A practical way to improve the performance of a distance relay is to adopt inverse-time operational characteristics within its first protected zone. For a digital relay, the accomplishment of inverse-time characteristics requires a suitable variable data-window filtering algorithm. In this paper, several typical variable data-window algorithms are evaluated and compared both in frequency domain and time domain. A new frequency-response analysis approach is developed in which the comprehensive filtering performances of the variable data-window algorithms are obtained. Based on the results of frequency response analysis and simulation tests, some adaptive techniques are proposed to achieve better estimation performance.