An algorithm for three-phase power system frequency measurement

A new algorithm for frequency measurement in an electric power system (EPS) under conditions of high harmonic distortions is presented. The algorithm is based on a combination of the Fourier method and zero-crossing technique which processes three-phase voltage signals at the site of the embedded digital relay. The Fourier method is used as a digital filter in order to form the calculated signals containing the fundamental frequency of the original signal. The zero-crossing technique is successively applied to the three-phase system formed by the three sine calculated components obtained by the Fourier method. The three-phase frequency measurement possesses better dynamic characteristics compared to the single-phase measurement. In addition, the three-phase measurement is more reliable since the algorithm allows frequency measurement even under conditions of single- or two-phase failures. By losing one or two input signals the algorithm loses only on dynamic performance but retains the stability and accuracy.