Tech Tip

WHAT ARE HARMONICS?

Harmonics And Their Effects On Power Distribution Systems

Harmonics in the electrical distribution system are the by-products of modern electronics. They are especially prevalent where there are large numbers of personal computers, printers, copiers, medical test equipment, fluorescent lighting and adjustable speed drives. Harmonics do no useful work; they degrade the level of power quality and efficiency in a commercial building or industrial facility.

Harmonics are currents or voltages with frequencies that are integer (whole number) multiples of the fundamental power frequency. If the fundamental frequency is 60Hz, the third harmonic is 180Hz, the fifth 300Hz, etc. Harmonics are created by non-linear loads, so-called because the current is not drawn as a smooth sine wave. When electronic equipment turns AC to DC, it draws current in pulses. These pulses cause distorted current wave shapes that are rich in harmonics. Electronic equipment will act as harmonic current generators. When these harmonic currents flow back into other parts of the power system they can also distort the voltage waveform which becomes non-sinusoidal. The distorted voltage can than effect other loads that share a transformer or branch circuit with the original harmonic load.

Reprinted by permission from Fluke.

HARMONIC (orig.-7/31/02)