New family of digital filters for phasor computation [power system relay protection]

A new family of digital filters is presented in this paper. They have been specially designed with the aim of reducing the leakage of the conventional Fourier filter. That reduction is achieved by changing its rectangular window by a new family of windows with smaller sidelobes. Considered as frequency responses of lowpass filters, the window spectra are translated to the fundamental frequency to form the bandpass filters. For durations greater than two cycles, the phasor estimates obtained with the new filters improve those of the conventional filter on a wide frequency band. Therefore, they are recommended for fault location and phasor measurement. However, its direct use on the protection function is discarded, because their duration needs to be of at least two cycles. To convince readers that this is a new useful technique, a theoretical explanation of the improved performance is also provided. Additionally, simulation results confirm the new filters improve the accuracy of the conventional algorithm by a factor of ten, and further improvement of the same order can be achieved by elongating the window.