Unbalance assessment and apparent power decomposition in the electric system of interharmonic-producing loads

Distortion levels on power systems have been continuously growing because of the increasing presence of loads, producing interharmonics as well as harmonics. Because in some loads such as arc furnaces, the interharmonic pollution is remarkable, the traditional power system unbalance indices and different apparent power quantities, in which only harmonic components were considered, create extraordinary errors. This paper proposes a beneficial method for extracting the actual amount of unbalance and the accurate apparent power quantities under nonsinusoidal, unbalanced conditions and in the presence of interharmonic components. In this regard, appropriate unbalance and harmonic distortion factors are defined. First, five case studies are presented to show the validity of the proposed indices. Then, in order to show the practicality of the introduced method, the proposed quality indices are calculated for data acquired through simulation of two typical steel industrial plants with a DC electric arc furnace. The results are compared with cases in which the interharmonic components have been neglected. On the basis of simulation studies, precision of the proposed method is represented, and it is shown that the obtained results are more accurate than those obtained by eliminating the interharmonic components. Copyright (c) 2012 John Wiley & Sons, Ltd.