The harmonic currents of commercial office buildings due to non-linear electronic equipment

In recent years there has been a growing concern for power system distortion. This is due in part to a proliferation of nonlinear electronic equipment such as personal computers, printers, fax machines, and medical test equipment. The power supplies used in this equipment are predominantly of the switching-mode variety which generate harmonic currents presenting serious problems to electric utilities. Of particular importance is the effect of harmonic distortion on three-phase, four-wire distribution systems which exist in most commercial and industrial buildings. This type of distribution system is susceptible to excessive neutral current and transformer heating which can lead to the eventual failure of the neutral conductor or the transformer. In this paper, the problems of high neutral currents and additional transformer losses due to harmonic currents are addressed. Harmonic current measurement results at an educational office building are presented. Finally, recommendations are made for overcoming the problems of harmonic current distortion.