Understanding Harmonics

Harmonics are undesirable components in the sinusoidal waveform of the AC Power supply. Harmonics occur as integral multiples of the fundamental frequency. That is, the third order harmonic will have a frequency of 3 times the fundamental frequency; 150 Hz which is 3 times the fundamental 50 Hz frequency. Harmonics affect power quality and equipment life and efficiency.

It is therefore necessary that Harmonics in any power system be monitored. Should Harmonics be present, they can be rectified by using suitable methods such as filters.

Causes of Harmonics

Harmonics are caused by Non-Linear Loads. The majority of electrical loads are linear meaning that the current varies sinusoidally with the voltage, though it may have a phase displacement.

However, of late, the proliferation of electronic devices such as Variable frequency drives, chopper circuits, inverters, etc cause non-linear loading of the power system. The current does not vary sinusoidally with the voltage. This leads to harmonics in the power system. The fundamental frequency will have many other frequencies superimposed on itself. This causes distortion of the waveform.

Using a mathematical technique known as Fast Fourier Transforms, the distorted AC waveform can be resolved into its component waveforms. Of the measured harmonics, the even harmonics(harmonics whose frequency are the fundamental frequency multiplied by even numbers such as 100Hz(2 *50) or 200Hz(4*50) get cancelled out and have no effect. For the study and management of Harmonics, only the odd harmonics are considered.

Effects of Harmonics

Harmonics have a wide range of effects such as heating of conductors, motors etc which can affect equipment efficiency. Besides, they can cause transient over/under voltages and can cause equipment failure.

Harmonic Analysis

If the problem of Harmonics is suspected, a harmonic analysis needs to be conducted. Harmonic analyzers are dedicated equipment to study the harmonics in a power supply. Typical Analyzers can resolve harmonics upto the 25th order.

Harmonics can be neutralized by means of Harmonic filters. Harmonics filters are usually LC circuits tuned to the frequency of the particular order of harmonics to be neutralized.

See Also:

Current and Voltage Harmonics

Harmonic Resonance

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