In fourier transform the complex waveform can be shown to 
be built of a series of sinusiodal waves whose frequencies 
are integral multiples of frequency of fundamental wave is 
harmonic functions are called harmonics

*Simply Harmonics is Integral multiple of fundamental 
frequency.* By means of different euipment different order 
harmonics are generated 3rd harmonics generated by AC 
Generator itself,5th harmonic generated by transformer& 
different order harmonics are generated by electronic 
circuit like rectifier,inverter o/p.
*Harmonics spoils many component in power system.
problems like mal function of MCBs,Excessive Heating in 
neutral conductor,excessive eddy current loss in conductor 
due to skin & proximity effect,it creates the problem in 
Motor & Tranformer iron loss.

Harmonics are frequency components that are whole number 
multiples of a fundamental frequency. For example, in a 
60Hz AC supply system, 2nd harmonic is 120Hz, 3rd harmonic 
is 180Hz and 4th is 240Hz.

Harmonics are most often caused by non-linear loads (eg 
transformers where the line current is distorted by the non-
linear B-H characteristics in the core), rectifier circuits 
and phase control circuits. In all these cases, the 
resulting load current waveform is not a pure sine wave, so 
harmonics are present.

Harmonics can cause all sort of problems such a voltage 
waveform distortion and the different harmonic frequency 
components causing different impedance values to appear in 
reactive components.

Harmonics Generally created in Non-Linear Circuits,for
eg.VFD,Inverters..etc.
It will create problem on waveform distortion.So designing
any power system with non-linear circuits harmonics to be
considered so that designing of the neutral cable size very
important.

Harmonics is Integral multiple of fundamental 
frequency.That means if the fundamental frequency is f, the 
harmonics have frequencies f, 2f, 3f, 4f and the property 
is that they are all periodic at the fundamental 
frequency.The sum of harmonics also periodic at that 
frequency.
If we see the generation of harmonics different order 
harmonics are generated 3rd harmonics generated by AC 
Generator itself,5th harmonic generated by transformer& 
different order harmonics are generated by electronic 
circuit like rectifier,inverter etc..
It creates many problems like in power systems are

Harmonics can cause all sort of problems Excessive Heating 
in 
neutral conductor,excessive eddy current loss in conductor 
due to skin & proximity effect,it creates the problem in 
Motor & Tranformer iron loss.It will give problem on 
waveform distortion. To avoid this designing of the neutral 
cable size very important.