Despite the name, electrical harmonics are terrible for data center harmony.

In a perfect world, the power supply feeding a data center would produce a smooth, sinusoidal waveform at one constant frequency – at 60 hertz in the US or 50 hertz in Europe. A single, pure wave like this contains no harmonics and thus no distortions of the waveform, which can otherwise cause increased losses, equipment overheating, interference, or degraded power quality.

But that’s in theory. In reality, data centers are filled with non-linear electrical loads, from office equipment and LED lighting to server equipment – all of which distort that perfect waveform.

These devices draw current in abrupt pulses rather than in a smooth, continuous manner, introducing harmonics that disrupt the system’s stability and lower the true power factor – a key metric of how efficiently electrical power is being used. Maximized at unity (1.0), the closer a facility’s power factor is to one, the more effectively it uses electricity, reducing energy losses and improving overall system efficiency.

Much of the problem stems from the widespread use of AC-to-DC converters like switching power supplies and diode-based rectifiers – both fundamental to modern computing infrastructure. Variable frequency drives (VFDs, or variable speed drives, VSDs, as they’re called in Europe), commonly found in HVAC systems, pumps, and cooling fans, and uninterruptible power supplies (UPSs) are among the most significant harmonic generators in data centers today.

Small ripples with big consequences

With the sheer volume of non-linear technology operating inside today’s data centers, recognizing and addressing the impact of harmonics has never been more important – and the problem often runs deeper than many realize. When harmonics infiltrate the system, the once smooth electrical wave becomes distorted – a point Thomas Shircel, data center application manager at ABB, illustrates vividly:

“Some people have equated this to nice rolling waves on an ocean. When you have harmonics, there are smaller waves between those – ripples that disrupt the smooth rolling motion.”

With a background in electrical engineering, Shircel has long championed awareness of harmonics in data center design. Now, with data centers scaling rapidly to meet the power demands of AI and high-performance computing, his message has become more pressing, critical to the reliability and scalability of the modern data center.

The costly impact of harmonics on the data center industry

With 90 percent or more of a data center’s total load coming from non-linear equipment, the cumulative impact of harmonics is substantial. Each of these devices – from servers to cooling systems (yes, the list goes on) – contributes its own harmonic content, distorting the overall electrical system and undermining power quality.

One major reason why harmonics must be addressed is simple: they waste energy.

“They cause overheating in your equipment, may require you to oversize your devices to support them, can cause issues with sensitive equipment, and over time, reduce the reliability of electrical devices,” explains Shircel.

In short, harmonics are more than just an electrical nuisance – they generate wasted energy that increases heat, shortens equipment lifespan, and drives up operational costs. That’s a serious concern in high-demand, mission-critical environments where every watt and degree can impact both performance and the bottom line.

“With modern equipment, just a 10°C increase in temperature can cut its life expectancy in half,” Shircel notes, adding:

“And while the electric utility must supply all the energy your system demands, harmonics ensure that some of that energy is simply wasted. You still pay for it – often seeing two to 10 percent higher electricity costs – while also dealing with the heat and reduced reliability they cause.”

This problem is exacerbated by the growing adoption of AI workloads in data centers, which are dramatically increasing power consumption. As power demand rises, so does the heat load – forcing non-linear devices to work harder, creating yet more harmonics in a compounding cycle of inefficiency.

Quantifying total harmonic distortion (THD) from all these non-linear sources is complex, but it’s a crucial step in modern data center design. By understanding where harmonics originate and how they propagate, operators can begin to take control – not just treating the symptoms, but addressing the root causes.

Understanding harmonic responsibility

Before choosing specific mitigation technologies, operators must first understand where inefficiencies exist and how they affect both the facility and the grid it connects to.

Conducting energy audits is a crucial first step in this process. These assessments analyze power consumption patterns, pinpoint wasteful practices, and identify opportunities for improvement. In many cases, harmonics are one of the hidden contributors to unnecessary energy losses.

Industry standards, such as IEEE 519, establish acceptable limits on the amount of harmonic distortion that electrical systems can produce without negatively impacting the utility grid. These codes not only encourage better design practices but also help ensure that facilities remain compliant and avoid penalties or excessive power quality issues downstream.

It’s important to note that while some technologies mitigate distortion locally, they do not address harmonics that may originate further upstream – at the utility or grid level – where broader power quality improvements may still be required.

Breaking the cycle: Preventive vs corrective strategies

According to Shircel, the good news is that harmonics within the data center can be effectively managed, and the tools already exist today. Through careful system design, proper equipment selection, and active power conversion technologies, data centers can significantly reduce harmonic distortion, improve power factor, and protect their infrastructure from unnecessary stress and inefficiency.

Some technologies prevent harmonics from forming in the first place, while others correct the distortions after they’ve entered the system. Within these two categories, solutions can be either active (using electronics to produce a smooth waveform) or passive (relying on circuit components to filter out unwanted frequencies).

Preventive measures

The most effective preventive devices are those that don’t create harmonics to begin with. Chief among these are ultra-low harmonic (ULH) drives, designed to maintain maximum power factor and minimize distortion.

Introduced back in the 90s, early six-pulse drive systems offered improvements in power factor and efficiency. However, these older designs still generated harmonics, prompting engineers to add reactors, filters, and design 12 and 18-pulse models to help mitigate harmonic distortion.

Modern ultra-low harmonic drives, such as ABB’s ACH580 ULH drive, have taken a step further. These systems maintain a unity power factor (the maximum, at value 1.0) across most of their operating range and can be programmed to lead or lag power factor, allowing facility managers to fine-tune power correction through building management systems.

“If your facility has a fair amount of ultra-low harmonic drives and the power factor is not in good shape, you can actively maintain correction around the clock. That’s something passive devices simply can’t do,” explains Shircel.

AFE drives go even further. Using advanced control electronics, they can create their own input waveform to ensure clean power flow from the grid – eliminating the harmonics at their source.

“With active front-end technology, we manipulate the input waveform so that energy flows into the system or back to the grid without generating residual harmonics. The result is unity power factor and a much cleaner electrical profile,” Shircel notes.

Corrective measures

When harmonics are already present, corrective solutions step in to neutralize their effects. These typically include harmonic filters and/or active filters to reduce distortion and ensure compliance with power quality standards.

Passive harmonic filters, for instance, offer a low-impedance path for dominant harmonic frequencies. Active filters use pulse width modulation technologies like active front-end drives, but the active filter creates harmonic frequencies that effectively cancel harmonics created by the non-linear loads.

For inductive systems with lagging displacement power factor, adding capacitors helps balance the power factor caused by inductive motor loads. The added capacitors offset the inductors, aligning voltage and current waves so that energy is used more efficiently rather than lost as heat.

While corrective measures are essential for existing facilities, they treat the symptoms rather than the source. For new builds and AI-ready data centers, preventive design offers the greatest long-term efficiency and reliability.

Best practices in data centers

The best practices for managing harmonics depend largely on the stage of your facility’s lifecycle – whether you’re designing a new data center or optimizing an existing one. Designing with harmonic reduction in mind from the start allows for significant long-term gains.

For instance, motors lose efficiency when operating at reduced loads, so optimizing system design to avoid idling or lightly loaded motors can directly improve power factor. Likewise, installing energy-efficient motors sized close to their rated load (rather than standard motors operating below capacity) helps maintain a high power factor from the get-go.

In existing data centers, the focus shifts to isolation and mitigation. Separating devices with high harmonics from more sensitive systems helps protect critical loads from the side effects of distortion, as Shircel explains:

“If you have a lot of devices that produce high harmonics, you want to isolate them from the rest of your facility so other equipment doesn’t suffer from excess heat or premature degradation.”

Tools like isolation transformers and active filters can help to limit the spread of harmonics, though they don’t eliminate energy losses – they simply localize the problem. The result is longer equipment life for sensitive systems, but continued inefficiency overall.

Another approach is harmonic cancellation, often achieved by adding filters to standard six-pulse drives. These filters absorb harmonic energy, but as Shircel points out:

“While the harmonics are prevented from reaching your electrical system, they’re still dissipated as heat.”

In other words, you protect your equipment but still waste energy. So, once harmonics have been introduced into a system, some energy loss is unavoidable. Even when active filters neutralize distortion, the process of balancing harmonic currents still consumes power.

Active harmonic filters use a similar technology to active front-end drives, but harmonics that in effect cancel out the distortion created from non-linear loads, creating waveforms much closer to a clean sinusoid upstream of the filter.

The key is to design and operate with harmonic distortion in mind from the very beginning, preventing harmonics from entering the data center in the first place. As harmonic distortion rises, the system’s true power factor falls – meaning more energy is wasted as reactive or distorted current. A low power factor not only increases utility costs but also places greater strain on electrical infrastructure, underscoring why proactive harmonic management is essential to achieving efficient and reliable data center operations.

The sticking point

As with most challenges in today’s data center industry, it ultimately comes down to cost. The barrier isn’t a lack of technology – it’s the balance between upfront investment and long-term payback. While harmonic migration components have become far more affordable and advanced in recent years, the initial expenditure can still deter operators focused on short-term budgets.

This financial hesitation appears at both ends of the spectrum: during new facility design, where harmonic prevention should be built in, and during expansion projects, where mitigation is often treated as a retrofit expense.

Yet, as Shircel emphasizes, early investment pays dividends quickly – particularly through energy savings and reduced operational losses:

“One of the big changes we’re seeing now is how power companies are incentivizing better power quality. Utilities often set a minimum power factor – for example, 0.85. If you fall below that, you pay penalties. But if you improve your power factor to 0.95 or higher, you can actually earn credits or reduced rates. So, when I move my facility from 0.85 to 0.95, my cost per kilowatt hour drops significantly, depending on my utility.”

In this way, technologies such as ULH drives with active front end (AFE) not only reduce wasted energy but can also deliver measurable financial returns, and in an era when data centers are consuming more energy than ever, these savings add up.

Shircel emphasizes that, with power quality a truly mission-critical factor in data center performance, harmonics are more than an electrical engineering problem; they’re a strategic opportunity:

“The very IT equipment that generates revenue also creates harmonics and threatens the infrastructure designed to power it. Adding to it, harmonics coming from cooling control devices like drives make the situation even more serious. But proactive harmonics management transforms those hidden liabilities into competitive advantages – improving efficiency and saving money in the long run.”

For more information, visit ABB.