Survey of harmonics measurements in electrical distribution systems

An assessment of the harmonics found in the electrical distribution system of several buildings in the three Department of Energy (DOE) Oak Ridge plants in Tennessee has yielded several conclusions useful in the design of electrical distribution systems. A preliminary survey to determine where significant amounts of harmonic currents or voltages existed in the distribution system was performed at several buildings by comparing readings taken with true root-mean-square (RMS) multimeters and averaging multimeters (nontrue RMS meters). From these measurements and subsequent calculations, facilities that appeared to have significant levels of harmonics present were analyzed with a power analyzer that could record waveforms and give the spectrum and magnitude of harmonics. Among the nonlinear loads for which sample waveforms are illustrated are fluorescent lighting (both magnetic and electronic ballasts), variable frequency drives, switch mode power supplies, and uninterruptible power supplies. A discussion as to how various harmonic waveforms come about as a result of these nonlinear loads is also outlined in this paper