Power system harmonics
Power system harmonics are the harmonic contents from the utility frequency. Harmonics are one kind of distortion to a voltage or current's waveform. This distortion is produced by non-linear devices connected to the power system. Since equipment is made to work at the utility frequency, harmonics can make it work wrong. This is one kind of power quality problem. It increases heating in power equipment.
Harmonics can be eliminated or reduced by using harmonic filter.