New Metod of Measuring of Symmetric Sequences of Three-Phase Voltage

Abstract

This article concerns the digital determination of three-phase quality indexes of electric power – coefficient of asymmetry on a negative sequence, rejection and oscillation of fundamental frequency voltage. These indexes are characterized by voltages of negative (VNS) and direct (VDS) sequences of fundamental frequency. For determination of VNS (after analog-digital transformation with tuning of frequency of measuring of instantaneous values of linear voltages) it is possible to take advantage of two linear operations – selection of linear voltages of    fundamental frequency and selection of measureable sequence. Traditional approach of VNS measuring uses just the same sequence of implementation of operations. Thus, accuracy requirements of selection of linear voltages of fundamental frequency are very high. And in obtained codes of linear voltages codes of VDS of fundamental frequency are dominant and inconclusive. Fundamental frequency is obtained further using complicated algorithm with the multi-bits calculations. Crushing down dominant and inconclusive VNS using addition of codes of instantaneous values of linear voltages after analog-digital transformation is proposed for determination of VNS of fundamental frequency. An algorithm is thus simplified in 20–50 times, accuracy requirements of subsequent selection of voltage of fundamental frequency decrease, VDS of most ultraharmonics disappears almost completely. VNS of fundamental frequency increases in 3 times as compared to its in linear voltages. VNS of fundamental frequency is further distinguished. The offered method of determination of voltage of symmetric constituents is characterized by simplicity and increased accuracy.