Methodology for evaluation of relay digital filters during a fault

This paper presents a new methodology for evaluation of digital filter techniques, whose main goal is to improve the insight about the advantages and disadvantages of the half- and one-cycle phasor estimation performance during transients. The voltage and current phasor estimation during transients affects the distance relay performance. With the adopted methodology, it is possible to identify which filters are not suitable for the distance protection. Therefore, the dynamic behaviour of the digital filters during a fault is investigated by using standardized performance indicators. In the evaluation, a comparative table is created based on a weighted average of the proposed indicators. The indicators used take into account the time response, frequency and processing power needed to compute the correct phasor. In the performance of the distance relays were evaluated the effects of fault resistance, inception angle, location and type of fault. According to the obtained results, the response time and amplitude directly depend on the adopted window size and the algorithm frequency response.