Harmonics are a by-product of non-linear loads, a load which draws a non-sinusoidal current.

In our increasingly technology-reliant society, harmonics are a growing concern when it comes to the management of electrical systems in both industrial and commercial sites. Despite the omnipresence of harmonics, a general lack of understanding particularly in terms of how best to mitigate them still exists.

It is something that engineers and electricians must be mindful of. Not only is it important in order to optimise the performance of devices, but also with a view to energy efficiency and changing electrical environments.

Power Tripping

The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms. Put simply, they place added strain on electrical networks. This can lead to the potential damage of – often crucial and costly – equipment. They threaten to disrupt the regular functioning of devices which leads to increased operating costs, namely through downtime and the cost of ongoing maintenance.

Additionally, harmonic currents increase the RMS current and compromise the quality of the supply voltage. This, in turn, causes power supply failures, such as tripping of circuit breakers or causing fuses to blow.

Harmonics not only cause plant down time and additional running costs, but in extreme cases can lead to being disconnected from the network.

Non-linear Loads and Distortion

So where does the problem arise? Essentially it boils down to the equipment such as switched-mode power supply (SMPS) equipment or variable speed drives, otherwise known as non-linear loads, of which there are an increasing amount.

A linear load is one where voltage is applied across a constant resistance resulting in a sinusoidal current. In contrast, non-linear loads occur when the resistance is not a constant and changes during each sine wave of the applied voltage waveform, resulting in a series of positive and negative pulses.

Equipment such as computers, printers, variable speed drives, chargers and TVs etc. tend to make up a significant percentage of non-linear loads in most electrical distribution systems.

Too much harmonic distortion can result in progressive damage to sensitive devices that rely on quality power.

There are two types of non-linear loads: single-phase and three-phase. Single-phase non-linear loads are most commonly found in office buildings or hospitals whereas three-phase non-linear loads feature more often in factories and industrial plants.

SMPS systems draw their current in short, high-amplitude pulses. This kind of pulse creates harmonic distortion that flows back into the power source, affecting any devices connected to the same point.

This process has been likened to the function of water pipes if you were to take a shower while someone turns cold and hot water on repeatedly at the sink, alternately burning or freezing you. The principle of harmonic distortion is the same, causing significant stress and interference to the equipment involved.

Harmonic distortion over time often leads to greater wear and tear on equipment such as transformers resulting in higher maintenance costs. Similar to filling your car with bad fuel, it will eventually lead to maintenance problems. The engine runs hotter, works harder and loses efficiency. It may cost less but in the long run you end up spending a lot more.

Costs Associated with Harmonics

There are numerous areas where harmonics can cause inefficiencies, depending on your electrical power system. For example in a manufacturing setting, unmanaged harmonics can cause a 10°C higher operating temperatures to maintain output. Ultimately this can reduce the life of a motor by 50%. For every percent of harmonic voltage distortion involving motors, an equal 1% of efficiency is lost each time. The rise in temperature dramatically reduces the lifespan as a result.

Large HVAC systems with a 370 or higher Kilowatt fan or pump load running at 5% voltage distortion instead of 1%, can cost upwards of$15,000 per year at 10 cents per kWh. This is in addition to the reduced lifespan of equipment caused by the heating effects of the harmonic currents.

Example of a distorted waveform caused by harmonics

Filtering The Harm Out of Harmonics

The challenge comes in being able to mitigate the issues created by harmonic distortion against a backdrop of vastly increasing numbers of non-linear loads in commercial and industrial buildings, such as variable speed drives and UPS systems in industrial buildings and office equipment like computers and photo copiers in commercial environments.

With an increasing amount of sensitive equipment and numerous ways to measure efficiency, the problem isn’t just affecting the business as a whole but employees collectively. Gaining a better awareness of electrical inefficiencies can help control capital expenses, gain AS/NZS61000.3.6 compliance, increased uptime and profits, and of course reduced energy expenses.

So how do you limit harmonics? If the cause of the harmonics is widespread then an active harmonic filter may be the most cost-effective option.

An active harmonic filter is installed on a network and measures the network current and injects an equal and opposite harmonic current to what it measures thereby cancelling out the harmonics such that the line current remains sinusoidal.

If restricted to just a few pieces of equipment such as variable speed drives, then the placement of passive filters in series with this equipment may be a more cost effective solution.

A passive filter consists of a series circuit of reactors capacitors that have a low impedance path compared to the rest of the network for the harmonic currents to flow into.

When designing new installations where large non linear loads will be used such as variable speed drives then using active front end drives offers another method of reducing harmonics without having to allow space for additional filtering equipment.

So What’s Next?

If you believe that your site may be experiencing harmonic related issues, the first step is to have a power quality survey carried out. Once the non-linear loads that are causing the majority of the harmonics have been identified, then the most appropriate harmonic mitigation strategy can be implemented.

Potential solutions range from an active harmonic filter designed to mitigate harmonics from multiple non-linear loads to the placement of a passive filter if the problem is restricted to just a few pieces of equipment to provide a more cost effective option.

Control Logic which is now an IPD Business, in partnership with ABB have harmonic specialists to help manage your electrical infrastructure to not only protect your electrical assets, and contribute to a ‘greener’ environment but also help improve a return on investment and boost the intrinsic value of your facility. Contact us by Clicking here.