Filtering requirements for distance relays are very critical, because they must estimate precisely and quickly the electrical distance to the fault, even with highly distorted input signals. A number of digital filtering algalrithms for distance relays have been proposed and some of them are in use in practical relays; however, power system evolution increases the corruption level of signals and imposes the necessity of continuing the research efforts in this area. In the present paper a comparative evaluation of different digital filtering algorithms for distance protection is performed. An evaluation method is proposed, which gives a comprehensive information about filter transient behavior on a widle frequency range of noise. The discussion is focused in well-known algorithms based on Fourier and Walsh transforms, and includes a recently proposed combined sine-cosine filter.

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