An algorithm for estimating derating of induction motors supplied with under/over unbalanced voltages using response surface methodology

Abstract

One of the adverse effects of unbalanced three-phase voltages on the induction motors (IMs) is overheating of the windings. The IMs should be loaded at less than their rated power in case of unbalanced supply voltages to prevent this overheating. Recent studies have pointed out that the maximum allowable loading ratio or derating factor (DF) of the IMs have various values for several combinations of the magnitude and angle of the complex voltage unbalance factor (CVUF) operating with a combination of unbalanced over and under voltage cases. This means that determination of DF requires plenty of experimental efforts for all possible unbalanced voltage conditions. In this study, the effective rms voltage definition which is defined in IEEE Standard 1459 is combined with the CVUF for proper identification of over and under unbalanced voltage conditions. An algorithm based on Response Surface Methodology (RSM) is proposed to estimate a precise DF for a broad range of unbalanced supply voltages. The simulation results using the d-q dynamic model of the IMs are presented to validate the effectiveness of the proposed algorithm. It is apparently figured out that the proposed algorithm has better accuracy compared to the conventional approach reported in NEMA Standard MG1.