Abstract— Extraction of fundamental components of both voltage and current is essential and is a challenge in digital distance protection. This paper introduces an effective filtering technique to fulfil this purpose. The technique proposed here is to use a windowed-sinc band-pass filter, which presents an outstanding immunity to both DC and harmonic components’ influence when used to extract fundamental components of voltage and current. Then, the computed impedance is an accurate indication of the fault point along a transmission line and experiences the least amount of fluctuation. Compared to existing algorithms, it has a faster determination of the fault impedance of the line under protection and it takes slightly more than half a cycle of 50Hz system to reach the accurate impedance value. An experiment was also conducted to verify the validity of the designed filter to extract 50Hz fundamental component.

Index Terms—digital relaying, impedance relay, windowed-sinc bandpass filter