What is harmonic distortion and why does it matter?

Harmonics are not visible, but their effects are. Harmonic distortions are repetitive and continuous deformations of the clean voltage or current waveforms.

Using Fourier analysis, a technique developed by the French mathematician, we can visualize the magnitude of harmonics present in the system.

Fourier showed that any distorted waveform is just a set of individual sine waves of different frequencies and amplitudes added together. The distorted waveform is made up of a sinusoidal fundamental curve, plus harmonics.

It is these individual higher order sine waves that are known as harmonics. Usually, we refer to power distortions in the frequency range under 2 kHz as “harmonic distortion”.

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Harmonic distortion of the waveform originates from non-linear loads connected to the power supply. All loads that draw non-sinusoidal current are referred to as non-linear loads. The biggest contributors to harmonics are:

• Switch mode power supplies
• Florescent and LED lighting equipment
• Uninterruptable power supplies (UPS)
• Frequency converters, also known as variable speed drives (VSD), variable frequency drives (VFD), AC drives or just drives

To reduce damage to equipment, regulations limit harmonics to low levels in power supply networks. Mitigation is not always necessary, but when required, harmonic mitigation devices can reduce harmonics to comply with these regulations. For successful harmonic mitigation there are many methods to choose between, including the use of harmonic filters, active front-end (AFE) drives, and more.

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Harmonic distortion in electrical systems damages equipment by causing overheating, voltage stress, and energy losses, which strain components and reduce their lifespan. The effects of more harmonic distortion are far-reaching, as they affect every piece of electrical equipment connected to the same system.

Excessive harmonic distortion can cause cables and motors to overheat. Motors, switchgear, fuses, cables, and sensitive measuring equipment are all impacted. Distortion with harmonic content can even interfere with critical telemetry and communication devices like Wi-Fi systems.

This can lead to premature equipment failure, such as blown fuses, tripped circuit breakers, or overheated motors, potentially affecting the entire industrial plant if no corrective measures, like harmonic filters or power quality improvements, are implemented.

The image shows the influence of harmonic distortion generators in overheating of electric motors.

Harmonic distortion increases power bills by increasing system losses and reducing overall system efficiency.

This wasted energy is a major operating cost issue for industrial users.

To reduce the total bill whilst still getting the same amount of useful power, we need to reduce harmonic distortion.

Electricity bills are made up of active and reactive power. Only the active power is usable, but we pay for both components. The extra cost can impact profitability.

Power distortions, including harmonics, are more than just annoying. They can stop your processes, causing downtime and interruptions to your production lines. They also affect the CAPEX when purchasing equipment and fuels to operate your plant, which has a major impact on operating cost targets.

Harmonic distortion and distortion in general also impact greenhouse gas (GHG) emission targets across all Scopes (Scope 1, 2 and 3 emissions). Distortion of the power supply results in these undesirable outcomes:

• Equipment is oversized in order to withstand damage
• Equipment operates inefficiently
• Distortion prevents energy efficiency initiatives from going ahead

The good news is that harmonic distortion, including higher frequency harmonics and lower order harmonics, can be mitigated. By putting measures in place to keep voltage distortion at low levels, you can:

• Increase transformer loading capability. This means you can reduce the size of transformers and generators required
• Prolong equipment life
• Increase equipment efficiency, for lower losses
• Reduce risk of power trips and production stoppages

Harmonics cause unreliability in networks by distorting the electrical waveforms, which can negatively affect the performance of sensitive equipment and systems. As more non-linear electrical devices are added to a system, the system becomes more vulnerable to these distortions.

Therefore, it is important to consider harmonics and how to mitigate them, to build a resilient system that does not fail.