Power quality characteristics of computer loads

Computer loads and systems can be found in all of society's industrial, commercial, and residential sectors. The nature of these loads is such that they distort the line-current waveforms and, in some cases, can significantly distort the supply-voltage waveforms causing disruption in computer system performance. The voltage (i.e., line-to-line, line-to-neutral and neutral-to-ground) and the phase current waveform characteristics of many computer loads are similar and reported in the literature. Some waveform patterns remain fairly stable during loading cycles, while other vary significantly and randomly. This paper presents several case studies to reveal the unique power quality characteristics of several commonly used computer systems (e.g., workstations, heating plant process computers, and electron microscopes). The dominant even- and odd-harmonic components of the waveforms are presented and discussed in some detail. This paper also discusses the impact of the computer loads on the supply voltage waveforms.