Presenters from the May 14, 2026, webcast, Power Distortion: The Silent Threat to Data Center Uptime, answer audience questions.
Power distortion insights:
- Harmonic distortion is becoming a critical design concern in high-density data centers, affecting system reliability, capacity and equipment lifespan through overheating, increased losses and protective device misoperation.
- Effective monitoring and mitigation of harmonics requires both measurement and design strategies, helping engineers identify distortion thresholds, interpret power quality data and implement solutions that protect uptime and electrical infrastructure.
Learning objectives:
- Understand how power distortion is generated in modern data center electrical systems.
- Recognize the warning signs and measurable indicators of power distortion.
- Interpret harmonic measurement data to determine when corrective action is required.
- Assess the impact of power distortion on uptime, capacity and equipment life.
As rack densities increase and electrical systems operate closer to design limits, harmonic distortion becomes more than a power quality metric. It becomes a design and operational risk. Knowing how to mitigate this risk is more important than ever in modern data center design.
Jose Garcia, Product Design Engineer and Lab Supervisor, and Aisha Bajwa, Field Applications Engineer, both from MTE LLC, discussed practical mitigation strategies and design approaches for controlling power distortion and protecting critical infrastructure.
After the presentation, audience members had a chance to ask questions to the experts. Below are some highlights from the Q&A, covering topics like harmonics prediction, active harmonic filters and harmonics mitigation strategies.
Is power factor (PF) used in measuring data center power quality? If yes, what is the average PF of a data center load?
Yes, but PF alone isnโt enough. Most data centers run high displacement PF (~0.95โ1.0), but distortion PF can drop overall PF into the 0.9โ0.98 range depending on harmonics.
Plants have had pumps and fans and chillers for decades, not to mention all the things in facilities like steel mills. Why the recent emphasis?
Loads changed. Older systems were mostly linear. Now we have VFDs, UPSs, and switch-mode power supplies everywhere, much higher harmonic contribution and tighter reliability requirements. Energy efficiency is driving all components to leverage VFDs and ECMs. This when combined with the total volume of equipment being installed results in significant harmonic issues. With more electronic-based equipment there is more sensitivity to electrical distortion within the system.
How would one calculate THD in a data center?
Using a one-line diagram of the facility, MTE is able to create harmonic studies to estimate harmonics in a data center. Harmonics can also be measured in the data center using a power quality meter. Measure current waveform and calculate:
THDi = โ(Iโยฒ + Iโยฒ + โฆ) / Iโ
Most power quality meters can measure THD directly.
How can we predict harmonics in a load?
For some equipment used in Europe, harmonic current performance may be available from the manufacturer. MTE has measured harmonics in many HVAC loads and has estimates on THID for each (Chillers 35%, Pumps 40%, EC Fans 40%)
Does MTE recommend and provide harmonic rate transformers, i.e., K-rated transformers?
Although MTE does not provide rate transformers, they can be useful for handling heating effects of harmonics, but they donโt reduce harmonics. Theyโre a survivability solution, not a mitigation solution.
Besides resonances, it appears that a lot of times multiple active harmonic filters in the same system seem to work against each other. How can you keep a UPS AHF from interacting with a chiller AHF?
This could occur when filters are both attempting to mitigate the same harmonic currents. This could be solved by control logic. Downstream active filters should be engaged and filtering prior to upstream filters. This allows the upstream AHF to address only the harmonic current that remains.
Why isn’t this problem solved at the component level? Roughly 30 years ago, the lighting industry went from electromagnetic ballasts to electronic ballasts, standardizing on ballasts with very low distortion (10-20% iTHD) and very high power factor (98-99%), while keeping costs low (~$0.05/W). It seems that the power converters on the data center peripheral equipment could be specified with comparable power converters at a reasonable cost and entirely eliminate this issue.
This is a function of cost + system variability. Some equipment already has low THD drives, but not universally, and system-level interactions (impedance, resonance) still require mitigation.
How early in the design would you recommend addressing harmonics?
The ideal time to consider harmonics is during the design of the electrical and mechanical systems. We are seeing more and more customers who did not address harmonics early and are paying the price. Adding harmonic solutions to a facility after it is designed and built can be a challenging task. Mechanical space and electrical infrastructure are key constraints that are easier to address upfront. Also adding these solutions while limiting facility downtime can be nearly impossible.
What is the maximum voltage drop across a harmonic mitigating filter?
Typically, 2โ5% at full load.
I have a distribution center that contains 60 material handling distribution panels that each serve 10 to 15 half horsepower (hp) motors that each have a VFD at each motor. I would assume that I would need to put a harmonic filter in front of each of the distribution panels. What type of filer would be best? And how do I size the filter?
This situation sounds like a perfect application for an active harmonic filter. To determine the best location to install the AHF MTE, we can review a line drawing of the system.
For an AI datacenter application, where IT equipment is upgraded every ~3-5 years, how do you specify harmonic filtering that lasts the effective life of the building? Or do you need to redesign your harmonic filtering with each reconfiguration of the IT load?
Many of the harmonic producing loads in a datacenter are related to cooling equipment (chillers, pumps, fans, CDUs). This equipment will likely be less dynamic than the IT equipment. If additional equipment is added to an existing data center, harmonics should be addressed.
Is there a way to predict expected harmonic distortion in a building design? How would we know when a harmonic filter is necessary?
If modeling or rules of thumb suggest IEEE 519 limits could be exceeded (low SC ratio + high nonlinear load), plan for mitigation.
What is the place for dynamic UPS in handling distortion?
While some UPS systems can isolate harmonics from the upstream power system, harmonics can still have negative impacts on the downstream network (wire overheating, equipment faulting and failure).
The power harmonics issue has been going on forever and I understand that power and human factors are the biggest reasons for outages. Is this issue much more critical due to AI and HPC deployments?
The issue has become more critical due mainly to scale. The amount of power AI data centers consume is much higher than previous data centers. This leads to a greater focus on efficiency, which results in more VFDs, which generate more harmonics.
Is it good practice to compliment harmonic filters with surge protective devices?
Yes, good practice. Different functions: SPD = transient protection, filter = steady-state distortion.
In HVAC equipment, is the primary source of harmonics VSDs or motors?
In HVAC, typically the VFDs are causing the harmonics, not the motors. Some motors have VFDs built into the motor. These are called electronically commutated motors (ECMs).
It seems that equipment vendors cannot provide harmonic emissions data. Where do you get your data to address harmonics during design before measuring the actual installation?
We have been fortunate to be able to measure harmonics on many different types of loads and can use that information to build harmonic estimations for specific types of equipment. Estimations can be made using typical drive characteristics + modeling + conservative assumptions.
Can harmonic resonance frequencies be calculated or do they need to be measured?
They can be calculated (impedance scan), but field measurement is often needed to confirm.
How is the harmonics power study done? Or is it just measured at the PCC or at individual equipment?
Utilizing a one-line diagram of the facility, MTE can create harmonics studies to estimate harmonics in a data center. MTE has data on many different types of harmonic loads and uses this information in our harmonics estimates. Harmonics can also be measured in the data center using a power quality meter.
How would one size and select correct AHF?
Size is based on harmonic current (not load current). Typical: 30โ50% of nonlinear load current, but must be confirmed with a study.
When is the best point in the data center design process to perform a harmonic analysis study? Should it be completed during design development before equipment is procured, or is it more appropriate later during commissioning once actual load data is available?
The ideal time to consider harmonics is during the design of the electrical and mechanical systems. We are seeing more and more customers who did not address harmonics early and are paying the price. Adding harmonic solutions to a facility after it is designed and built can be a challenging task. Mechanical space and electrical infrastructure are key constraints that are easier to address upfront. Also adding these solutions while limiting facility downtime can be nearly impossible.
Do Harmonics relate to LEAD | LAG – power factor – VARS in power systems? If you control one – does that affect the other?
Harmonics and lead/lag PF are related but different. VARs affect displacement PF (fundamental), while harmonics affect distortion PF. Fixing one does not fix the other.
What are the best techniques for prediction/modeling of harmonics?
For modeling, harmonic load flow + frequency (impedance) scan using detailed system modeling (ETAP, SKM, PSCAD)
But more practically, harmonic load flow โ calculates expected THD based on modeled sources (VFDs, UPS, etc.)
Frequency / impedance scan โ identifies resonance points in the system
Device-based modeling โ uses actual harmonic spectra or typical profiles for equipment
Which level of the distribution (MV, LV, rack level) would you recommend for optimal harmonic mitigation?
Typically, LV distribution. Harmonics should be addressed as close to the source of the harmonics as possible.
These slides seem keyed around a cloud data center architecture. Does anything presented change with AI workloads and the harmonics that may be introduced in an AI data center deployment?
The fundamentals are the same, but AI workloads increase power density and dynamic loading, which can raise harmonic levels, so mitigation and power quality design become more critical, not different.
Is it always recommended to request harmonic filters from the manufacturer when chillers are provided with a VFD?
Since chiller loads are so large, addressing harmonics on each chiller is very common. This can be done by adding requirements to the chiller specs. Chiller harmonics could also be addressed at the system level, however this is less common.
What is the maximum amperage rating on those Syntrix active filters at the switchgear level?
For a single active filter, we can parallel up to 16, 150A modules totaling 2400A of correcting current.
Are harmonic filters needed for chillers installed with variable frequency drives?
Not required in every case, but VFD chillers are a major harmonic source. In most cases you will need to mitigate those harmonics. If the system has high VFD loading or needs to meet IEEE 519 limits, harmonic mitigation (reactors, low-harmonic drives, or filters) is typically required.
Could you explain the relationship between the system short circuit current and load current?
Short-circuit current represents system strength, while load current represents demand. Their ratio (Isc/IL) indicates how stiff the system is, and a higher ratio means a stronger system and typically lower harmonic impact.
I’ve always understood resonance to be a point where the harmonic waves build on themselves; could you explain what resonance looks like from a wave perspective?
Resonance = the system keeps getting โpushedโ at exactly the right timing, so every new wave lands on top of the previous one and grows the amplitude.
