Evaluating the Implementation of a Modified Method for Calculating Symmetrical Components Based on Synchronous Measurements of Instantaneous Currents in Three Phases in Operating Power Supply Systems

The trend of increasing the number and installed capacity of single-phase non-linear power consumers leads to deteriorated power quality. Unbalance in zero and negative sequences is a criterion for assessing the power quality. Moreover, the zero sequence unbalance factor is determined by the zero sequence current magnitude. The study is aimed at empirically justifying the advantages of implementing a method based on measuring the instantaneous currents synchronously in three phases over a single period to evaluate the zero sequence unbalance factor compared to the symmetrical component method using the phase factor for a more accurate assessment of current and voltage unbalance in distribution power grids. To achieve this goal, a test bench and a computer model of the power supply system were developed and built. The developed bench and computer model allowed for obtaining an array of synchronously measured instantaneous currents and voltages for each phase and in the neutral conductor with non-sinusoidal load magnitude andtypevarying independently for each phase. Thereat, the criterion for assessing the accuracy of calculating the zero sequence unbalance factor was the magnitude of the current in the neutral conductor. The use of the symmetrical component method for determining the zero sequence current in the case of amplitude-phase unbalance with active and inductive sinusoidal and non-sinusoidal loads givesan unacceptable error. To reduce errors in calculating the zero sequence current, the implementation of a method based on measuring the instantaneous currents synchronously in three phases over a single period is advisable.