Definitions
A harmonic voltage is a sinusoidal voltage whose frequency is an integer multiple of the mains voltage fundamental frequency.
Harmonic sources
The devices and systems that produce harmonics are present in every sector, i.e., the industrial, commercial and residential sectors. Harmonics are produced by non-linear loads (i.e. loads that, although powered by a sinusoidal voltage, create a non-linear, distorted current wave).
Examples of non-linear loads：
-Welding equipment (welding machines, arc furnaces, induction furnaces, rectifiers).
-Variable speed drives for DC or asynchronous motors
-UPS.
-Office equipment (computers, photocopiers, faxes, etc.). -Household appliances (television, microwave ovens, fluorescent lamps).
-Some devices with magnetic saturation (transformers).
