Harmonics in Transformers What are Harmonics?

What are Harmonics ?

Sinusoidal waveforms whose frequencies are integral multiples of the frequency of the fundamental.
 

For a 60Hz fundamental:

3rd Harmonic =3 x 60Hz=180Hz

5th Harmonic =5 x 60Hz=300Hz

When a waveform comprises a fundamental component and one or more harmonic components, the resulting waveform is non-sinusoidal in nature.

What causes Harmonics ?

Non-Linear Loads i.e. Loads resulting in non-sinusoidal waveforms

Examples of non-linear loads are:
    Switched mode power supplies.
    Office equipment such as P.C.’s, Fax machines, Copiers
    Rectifiers
    Adjustable speed drives
    Electric discharge lighting

Harmonic levels vary according to the type of load.

The effects of Harmonics on transformers

1. Additional heat generated in the windings.
Harmonic currents cause additional heating,
mostly in the form of additional winding eddy current losses.

2. Increased impedance
Since impedance is proportional to frequency, harmonic currents result in additional impedance components, which add to the impedance due to the fundamental component.

3. Increased core excitation.
Harmonic currents flowing through the power system impedances result in voltage drops which cause voltage distortion.