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In recent years, there has been much discussion and interest on the subject of power quality. Whereas in the past, power received from the Regional Electricity Company was a pure sinusoidal waveform i.e. clean power - more frequently today, industrial plants are finding they have to deal with the problem of “dirty power”. Dirty power includes a variety of voltage and current contamination on the sinusoidal wave in the form of short-term transients or steady state, continuous distortions.

Due to the demand in industry and commerce for the stability, accuracy and flexibility of control over electrical equipment, several developments occurred. The most relevant development to harmonics was the introduction of low cost power diodes and thyristors. Now used widely for rectifiers circuits for U.P.S. systems, static converts and D.C. motor control, these modern devices replace the mercury Arc rectifiers, but also create new and challenging conditions for the power engineer of today. One of these conditions is the production of harmonic currents.

What are Harmonics?

Harmonic currents can cause an unacceptable disturbance on the supply network and adversely affect the operation of other electrical equipment including power factor correction capacitors.

All complex waveforms can be resolved into a series of sinusoidal waves of various frequencies, hence any complex waveform is the sum of a number of odd and even harmonics of lesser or greater value. The diagram below shows examples of several harmonics compared to the sinusoidal wave and the resultant wave after distortion.

sinusoidal wave

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