A non linear load is that load which takes current suddenly in pulses and not in the sinusoidal way so its current waveform is distorted or non sinusoidal.
These loads produce harmonic disturbances in the AC electrical systems which includes the quality of power.
In a linear load, for instance resistive heater or an incandescent bulb, the current waveform is almost in phase with the voltage waveform (both being sinusoidal).
However, in non-linear loads where the load current does not vary proportionally to the voltage across the load.
Examples of nonlinear loads are any nonlinear loads containing power electronics such as:
- Variable Frequency drives or VFDs,
- Computers and other Electronic Equipment,
- LED lights,
- Switch Mode Power Supply and
- Uninterruptible Power Supply or UPS.
These loads discharge currents in short pulses, and create harmonics which are inevitable aspects which may frustrate effectiveness, transformer overheating, and interference with other equipment sharing the same electrical grid.
Non-linear loads produce harmonics and IEEE 519 advises that allowable harmonics should not be exceeded as they have the capability of causing problems in the electrical power system and the equipment. Other standards like IEC 61000 also cover EMC, specifically limits on emission of harmonics from nonlinear loads.