This is a very important aspect of power quality and relates to distortion of the voltage and current waveforms. Beyond certain levels harmonic distortion can cause all manner of problems for customers and utility networks.
Harmonic distortion that is causing problems can ordinarily be identified by a standard power quality survey, however, this area can get quite complex especially if transient harmonic resonance phenomena are present. The ideal power supply waveform is sinusoidal in shape. Modern electronic and power-electronic equipment however has a current waveform that is very different to a sine wave. This tends to distort the voltage waveform and so the effect can be spread to many users. If the harmonic distortion is high negative effects can arise. Such effects can include; increased neutral current, cables, transformers and other equipment running hotter then normal, various electronic controllers misbehaving, etc.
Serious negative effects of high harmonics are not particularly prevalent but do certainly exist. As harmonic generating loads are on the increase the subject is very topical and the effects need to be monitored closely. In those areas where harmonic distortion is a problem it should be identified and rectified early so that damage, energy losses, or malfunction can be prevented.