Total Harmonic Distortion: 11 Things (2024) You Need to Know

Look through the manual for speakers, headphones, MP3 players, amplifiers, etc., and you’re likely to find a specification called total harmonic distortion (THD).

In this blog, we’ll discuss what THD is and why it’s important to consider when using equipment (including solar panels!).

1. What is total harmonic distortion?

Total Harmonic Distortion, often abbreviated as THD, refers to any distortion on a sine wave.

In the context of power generation, it is the difference in the current (or voltage) of a load compared to what a perfect wave could deliver.

In audio devices, THD compares the input and output of audio signals with the difference measured as a percentage.

THD is often listed as 0.02 percent with specified conditions of frequency and equivalent voltage in parenthesis (ex: 1 kHz 1 Vrms).

The percentage you find represents the harmonic distortion or deviation of the output signal.

Lower percentages are better.

An output signal is a reproduction.

It is never a perfect copy of the input signal, especially when several components are involved in an audio system.

As a result, the higher the THD, the more distortion you will hear in the output.

2. What are harmonic frequencies?

In a power system, harmonics are voltages and/or currents present in the system at some multiple of the fundamental frequency.

They are any harmonics that exist in the system except the fundamental frequency.

Said differently, harmonics appear as a distortion of the purely sinusoidal waveform on the power line.

The best way to visualize the difference between fundamental and harmonic frequencies is to think of an instrument.

When you play a note on a musical instrument it produces not only the desired note but a series of select harmonics, which gives the instrument a unique timbre.

For this reason, when a violin plays a middle A note it sounds different than when a cello plays a middle A note.

The violin will produce a fundamental frequency of 440 Hz while also reproducing harmonics (multiples of the fundamental frequency) at 880 Hz, 1220 Hz, 1760 Hz, etc.

On the other hand, if the cello plays the same middle A note, it still sounds like a cello because of its particular fundamental and harmonic frequencies.

3. What is the importance of total harmonic distortion in power systems?

When total harmonic distortion increases beyond a certain point, a host of issues can occur, including overheating of the equipment connected to it, disruption and higher electric bills.

4. How much total harmonic distortion is acceptable?

There is no national standard around total harmonic distortion, but according to IEEE (Institute of Electrical Engineers) Standard 519, the THD measurement should be less than 5%.

IEEE 519 also states that no one harmonic can be more than 3% of the fundamental frequency.

Since this is the standard, most computers and other major electronic devices require AC sources with a total harmonic distortion factor of 5% or less.

5. What causes high total harmonic distortion?

Non-linear loads are the primary cause of harmonics.

These loads draw power in short bursts, which creates voltage distortion in the distribution equipment and whatever is connected to it.

Most modern equipment, such as computers, printers and photocopiers, produce non-linear loads.

6. How does total harmonic distortion affect your power bill?

Total harmonic distortion is inversely proportional to power factor.

If a given load has a high power factor, then its total harmonic distortion factor should be low and the system will be more efficient.

Conversely, when total harmonic distortion is too high, the system will be less efficient.

Therefore, harmonic distortion is is one of the biggest factors that contributes to wasted energy and increased electricity bills.

7. How does total harmonic distortion factor into power metering?

Harmonic distortion can negatively impact electrical equipment and lead to the degradation of individual components.

Increased current leads to excessive heat and interferences with over-the-wire communications.

When these two factors are left unchecked, they can cause long-term damage to both the electrical equipment and the entire system.

For this reason, both individual devices and commercial power facilities must be monitored for efficiency purposes.

Power meters can measure many parameters like reactive energy, apparent power factors, and line frequency, which provide facility managers with the information they need to take the appropriate steps.

8. What does total harmonic distortion mean for your power equipment?

When power sources with higher harmonic distortion overheat, they short out and damage the internal electrical components of connected equipment.

When power sources have higher levels of harmonic distortion, they can also cause subtle malfunction in the equipment connected.

In some cases, this can have serious consequences.

For the most part, THD doesn’t have major effects on basic power tools.

However, a tool with a digital interface and advanced circuitry could encounter any of the following:

bulletMinor malfunctions that affect performance (i.e., the inconsistent heat output from an automatic welder)

bulletA shut down to protect against large spikes

bulletEarlier breakdowns

These issues will ultimately impact the quality of your equipment’s output and cost you thousands of dollars in repairs and replacement parts.

9. What should you take away about total harmonic as a consumer?

Total harmonic distortion impacts everything from music to electronics.

As a consumer, you’ll be able to find total harmonic distortion information on the product specification table or the label.

As we mentioned earlier, the IEEE Standard 519 recommends that computer and allied equipment (i.e., programmable controllers) use an AC power source with no more than 5 percent harmonic voltage distortion with no single harmonic being more than 3 percent.

If you are using an off grid power source, investing in a clean and consistent power generator is a great way to save yourself time, money, and hassle down the road.

10. What are the power quality issues caused by harmonic distortion in photovoltaic systems?

Photovoltaic systems represent inverter-based types of generators.

These consist of photovoltaic panels that generate direct current (DC) power and an inverter that continually transforms the DC power into alternating current (AC) power.

PV inverters use semiconductor devices to transform the DC power into controlled AC power by using Pulse Width Modulation (PWM) switching.

The inverter is what allows the photovoltaic system to be connected to an AC electrical installation.

PV systems are thus composed of both DC power sources and electronic equipment.

As a result, they can struggle with some power quality issues, like residual DC currents, harmonics, or imbalance.

Thus, generally speaking, most inverters generate some residual DC currents.

11. What should you know about solar (PV) panels, electrical grids and harmonic distortion?

There has been a rapid installation of PV systems in low voltage (LV) distribution networks, and as a result, power quality has become a key concern for governments, grid companies, and PV plant owners.

To help with these issues, strict regulations have been introduced to limit harmonics in grid-connected PV systems.

If the harmonic content of the PV system isn’t up to the standard of the power plant, then it must be reconstructed by adding harmonic filters and other equipment.

Otherwise, it faces the risk of shutdown.

Not only is harmonic distortion an issue for the grid, but it also impacts a PV system’s ability to perform at optimal levels.

By keeping total harmonic distortion levels on a PV system low, you ensure proper operation of equipment and a longer equipment life span.

PV owners must thus consider using filters as well as devices to monitor total harmonic distortion to avoid inefficiencies, higher costs, or catastrophic consequences.

Final Thoughts

Total harmonic distortion can affect both sound and power.

Knowing how this plays a role in music, power equipment, and solar power is useful in daily life.

We recommend learning about harmonic distortion as it pertains to PV systems before installing solar panels!

With this knowledge, you can take the appropriate protection measures to avoid damaging equipment and navigate safety concerns.

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Erika Gokce Capital

Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.


2 thoughts on “Total Harmonic Distortion: 11 Things (2024) You Need to Know”

  1. Is there a conditioner, filter, or a way of reduce THD from my generator? My old sump pump never worked again after using it on the sump (a capacitor blew) and 1 out of 3 UPS in the house refused to use the electricity from my generator.

    I’m sure if I converted the Generator’s AC to DC and then back to AC I would reduce the THD but I’m hoping there is a plug and play easier way.

    Thoughts ?


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