Impact of unbalance on power system harmonics

Due to the ever increasing number of nonlinear loads on distribution systems, the existence of harmonics, nowadays, is inevitable. As a result voltage and current waveforms are rarely sinusoidal. In addition, distribution systems are quite often unbalanced in nature. This necessitates the study of the combined effect of unbalance and nonlinearity on power system voltages and currents. Results of simulations carried out to study the effect of unbalance on the harmonics injected by a 6-pulse converter drive, are presented in this paper. Initial analysis is carried out in the phasor domain, and this is corroborated with results obtained by decomposing individual harmonics into symmetrical components. The performance of arc furnace models, under unbalanced conditions is also investigated, to observe the impact of unbalance on the modeling of nonlinear loads.