In power systems, Harmonics are multiples of the fundamental frequency. Thus, the third order harmonic is the third multiple of the fundamental frequency. This type of harmonics is generated in non-linear loads. Examples of nonlinear loads include transistors, electrical motors, and the non-ideal transformer.

1. How To Check
For Harmonics
In Electrical
Power
Systems

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3. Introduction
• Harmonics are electric voltages and currents on an electric
power system that can cause power quality problems.
• Because equipment and machinery can malfunction or fail in
the presence of high harmonic voltage and/or current levels,
harmonic distortion has become a growing concern for facility
managers, users of automation equipment, and engineers.
• While the presence of harmonics won't make it impossible for
a factory or office to operate, the degree of impact depends
on how much the power system can withstand and how
susceptible the equipment is to harmonic distortion.

4. What Causes Harmonics?
• Harmonics are created by electronic equipment with nonlinear
loads drawing in current in abrupt short pulses.
• The short pulses cause distorted current waveforms, which in
turn cause harmonic currents to flow back into other parts of
the power system.
• Harmonics are especially prevalent when there are many
personal computers, laser printers, fax machines, copiers, or
medical test equipment, fluorescent lighting, uninterruptible
power supplies (UPSs), and variable speed drives all on the
same electrical system.

5. Common Problems Caused by Harmonics
• Overloading Neutral Conductors
• Overheating Transformers and Increased
Associated Losses
• Nuisance Tripping of Circuit Breakers

6. Overloading Neutral Conductors
• The three-phase system consists of three individual
phase conductors and a neutral conductor.
• If all the phase conductors carry the same current, the
phase currents tend to cancel one another out provided
there is a balanced load.
• This balanced load makes it possible to reduce the size
of the neutral conductor.
• Unfortunately, switched mode power supplies used in
computers have a very high third-harmonic current.
• While harmonic currents cancel out on the neutral wire,
the third harmonic current is additive in the neutral.

7. Overheating Transformers and Increased
Associated Losses
• For transformers feeding harmonic-producing loads, the
eddy current loss in the windings is the most dominant
loss component in the transformer.
• This eddy current loss increases proportionate to the
square of the product's harmonic current and its
corresponding frequency.
• The total transformer loss to a fully loaded transformer
supplying to a nonlinear load is twice as high as for an
equivalent linear load.

8. Nuisance Tripping of Circuit Breakers
• All circuits containing capacitance and inductance have one
or more resonant frequencies. When any of the resonant
frequencies correspond to the harmonic frequency
produced by nonlinear loads, harmonic resonance can occur.
• Voltage and current during resonant frequency can be highly
distorted.
• This distortion can cause nuisance tripping in an electrical
power system, which can ultimately result in production
losses.

9. How to Diagnose and Fix Harmonics
• A harmonics analyzer is the most effective
instrument for performing detailed analysis of power
quality to determine the wave shapes of voltage and
current on respective frequency spectrums.
• A harmonic analyzer is also useful in instances where
the lack of obvious symptoms prevent you from
determining if harmonics are a cause for concern.

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Harmonics Measurement