How to prevent and correct the harmonic distortion on electrical supply

Harmonic distortion causes a range of problems due to the waveform distortion that affects the voltage and current, such as overheating conductors (especially the neutral) and increasing the power transmitted, which can reduce the power factor of the grid. It can destabilise electricity circuits, triggering the circuit breaker for no apparent reason, cause faults in electronic devices, and even ruin capacitor banks.

What is Total Harmonic Distortion (THD) and how is it measured?

To find and quantify the amount of harmonic distortion present in an electrical or audio signal, we need to analyse the Total Harmonic Distortion (THD). Harmonic distortion occurs when components of additional frequencies are created that are not present in the original signal. These can be caused by the non-linearity of the electrical circuits, the saturation of amplifiers and electromagnetic interference, among other factors.

THD was originally expressed as a percentage that shows the relation between the energy of the fundamental signal and the energy of the harmonic components. A low level of THD means that the signal is free of harmonic distortion, while a high THD indicates a higher amount of distortion.

How can we make an effective harmonic survey?

The important point is not to wait until a fault occurs before analysing the harmonic distortion, so we have to get down to work and check all the equipment and devices which are more vulnerable to disturbances in the grid, and deal immediately with any indications of distortion that we may detect.

• If you are installing a new capacitor bank it is important to know what the Total Harmonic Distortion is to make sure that disturbances in the grid do not damage the equipment.
• If your capacitor bank has more frequent faults than is normal, it is advisable to carry out a harmonics survey to find out whether these faults are being caused by distortion.
• Any installation that suffers from repeated circuit breaking for no apparent reason at any time should also be checked for distortion so that any measures necessary to solve the problem can be applied.
• Companies with a lot of computer equipment should carry out a harmonics survey as a preventive measure to avoid damage to its devices, to protect them from disturbances in the grid. Companies with power electronics, which are the principal source of harmonics, also have to be surveyed.
• Industrial premises which use discharge lighting must comply with an analysis of their total harmonic distortion. Even when there are no productive processes as such, the harmonic distortion caused by non-linear loads can cause problems.
• The electronic controls of cooling systems and air-conditioning equipment render cold storage facilities vulnerable to problems with harmonic currents, so they also need to be measured.
• A harmonics survey is important for agricultural facilities as these make use of automatic controls and electronic starters. This would avoid problems with irrigation pumps.

What are the benefits of a harmonic survey?

• It will reduce the negative effects of harmonics on the installation.
• It will help to reduce operating costs and electricity consumption.
• It will extend the working life of equipment. Single-phase machines can last up to 32% longer, three-phase machines 18% and transformers 5%.
• It will reduce losses due to overloads and cables overheating.
• It will reduce the sources of distortion in the system.
• It will make the loads in the system more stable.
• It will make the grid more reliable.

Effects of harmonic distortion on audio systems.

Disturbances in the grid do not just damage electrical installations, they can also affect audio systems.

One of the most common effects of harmonic distortion is the loss of sound quality, introducing unwanted noise that can “deform” the original tone of the signal.

Audio fatigue is another kind of damage caused by these disturbances. Listening to music or sounds at high levels of harmonic distortion can affect your hearing, causing stress by forcing the brain to try to process the distorted signal.

These disturbances in the grid can compromise the precision and fidelity of the audio equipment used in recording studios, and high-quality audio systems. The presence of harmonic distortion can trigger problems of electromagnetic interference that can affect the performance of electronic systems and equipment.

The problem of harmonic currents in the distribution and consumption of electricity is increasingly common in our homes and in the working environment. The increasing number of power electronics devices in our daily lives exposes us to a greater risk of being affected by harmonics, especially in financial terms. This is why preventing and correcting harmonic distortion through a survey of the Total Harmonic Distortion is an important step or measure to monitor the correct operation and quality of the electrical signal, and one which will help to lower operating costs and electricity consumption.