Elimination of aperiodic components of measuring elements of relay protection

Abstract

The authors propose the algorithms to calculate the actual values of currents and their derivatives. The algorithms allow a sharp reduction in the aperiodic components of currents in the calculated actual values and their derivatives. The algorithms are developed to calculate the instantaneous values of positive- and negative-sequence currents when the information obtained during a time interval equal to two milliseconds or less is used. An algorithm is devised to calculate the sinusoidal components of the currents in the presence of aperiodic components in the samples. To eliminate the disoperation of digital relay protection and improve the accuracy of fault location, it is necessary to eliminate the influence of aperiodic components in the currents drawn to the measuring devices of relay protection. The algorithm completely eliminates the aperiodic component at any time constants and is implemented by four samples of currents. The four samples of currents separated by three sampling intervals are sufficient for calculating all the parameters of currents, including the positive and negative-sequence currents, in particular in the case when the magnetic cores of current transformers reach saturation. The proposed methods for setting the industrial frequency parameters to avoid the aperiodic components in short-circuit currents are based on the algorithms that process the data from three and four samples of currents.