What is a nonlinear load?

With harmonics, what is a nonlinear load and what does it mean?

Waveforms show the difference between nonlinear andlinear loads. A waveform depicts sine waves of current and voltage. Take for instance a waveform that reflects the voltage and the current in nice clean, 60 Hz sine waves. With this particular waveform, the current looks like the voltage and so what we have is a linear load. 

When there are nonlinear loads, the current does not look like the voltage on a waveform. Harmonics come from the loads so in this case we have current that is affecting the voltage. As we pull that current through the system, the nonlinear load creates current distortion, which then causes voltage distortion.

Again, with linear loads, the voltage and the current sine waves are going to look the same. Current that is drawn from a regular motor or a light can look like the clean voltage, even if it is not in phase or a little bit leading or lagging—it depends on the power factor of the load. 

With nonlinear loads, the current is not going to look like the voltage. The more drives or the more distorted current we add—the more voltage distortion we have on the system.