By Jason Axelson, Fluke Subject Matter Expert, Power Quality
Harmonics in data centers pose significant challenges to operations, increase utility costs, threaten downtime, and eventually damage equipment. Sometimes, symptoms are detected through hot panels, tripped breakers, UPS issues, or buzzing sounds emitted by equipment. Other times, harmonics remain undetected until a major disruption or damage to equipment occurs.
Diagnosing harmonics involves identifying the problem and intervening with corrective action to prevent energy loss, damage, or even downtime. In this article, we’ll discuss troubleshooting harmonics in electrical systems and steps you can take to reduce the harmful effects of harmonics.
Step-by-Step Guide to Troubleshooting Harmonic Distortion
Step 1: Confirm Harmonic Distortion is Present
Harmonics may be present in data centers without causing damage. To confirm if total harmonic distortion (THD) exceeds recommended limits, check the power distribution unit (PDU) and uninterruptible power supply (UPS) manufacturer’s recommendations to see a) how both devices recognize harmonics, and b) what level of THD would trigger UPS tripping due to poor power quality or switching to battery backup, both of which can shorten battery life and compromise uptime.
Acceptable limits of voltage harmonics vs. current harmonics vary depending on the equipment. Typically, recommended levels are 5% for voltage harmonics and 20% for current harmonics. IEEE 519-2022 thresholds are 8% for voltage and upwards of 20% for current, but these recommendations apply to the point of common coupling (PCC) between you and your neighbor on the utility transformer. The questions you need to answer are 1. Is there a problem being diagnosed? and 2. How much voltage distortion happens under load?
Using a specialized tool like the Fluke 1777 Three-Phase Power Quality Analyzer, which supports waveform capture, can help identify waveform distortion. These tools record events that fall outside defined thresholds, such as voltage dips and swells. Check what is happening with the current and voltage by observing trends and waveshape data.
Step 2: Isolate the Source of Distortion
Once you’ve identified harmonics, you need to perform source tracing to isolate the distortion source. First, you must determine if the harmonics are coming from upstream or downstream. You can do this by looking at the harmonic power measurement on your analyzer. A positive harmonic power reading suggests the distortion is coming from upstream. A negative reading indicates the harmonics are load-induced and generated by your equipment.
Typically, harmonic-inducing loads include energizing and/or saturating transformers, UPSs, IT equipment (servers, storage, etc.), variable frequency drives (VFDs), LED lighting systems, and inverters or power converters.
To understand harmonic directionality, the Fluke 1777 is required. Other tools can help identify harmonics, but they can’t quantify the directionality of the harmonics. They also aren’t as helpful with source identification.
Step 3: Apply the Right Remediation
There are several options for fixing harmonic distortion in data centers. Choosing the most suitable fix depends on the source of the harmonics.
Load Balancing
Load balancing reduces neutral current and the resulting thermal stress on transformers, freeing up capacity and extending equipment lifespan.
Installing Harmonic Filters
Harmonic filters for data centers have two types: active and passive. Passive filters are designed to target specific harmonic frequencies and are typically more cost-effective. But, when improperly tuned, passive filters can introduce resonance to the system, potentially amplifying distortion instead of reducing it. Active filters automatically self-adjust to eliminate harmonic frequencies, but they can cost more.
Equipment Replacement
During measurement, high neutral currents can indicate heating in the transformer. Thermal imaging can also be used to identify the problem, along with comparisons to the manufacturer’s specifications. If your transformer doesn’t have a K rating (or has a low rating), replacing it with a K-13 or K-20 rated transformer can mitigate harmonics. K-rated transformers are designed to handle harmonics without overheating, improving reliability and equipment lifespan. The Fluke 1777 can also calculate transformer K-ratings if you’re unsure.
Reconfiguring Loads or Separating Circuits
Reconfiguring loads or separating circuits is an effective harmonics remediation strategy. By redistributing harmonic-generating equipment or isolating it from sensitive loads, you can minimize the impact of distortion on critical systems. Replacing older equipment, such as traditional UPS systems, with improved transformerless UPS models can also reduce harmonic generation at the source. In some cases, simply relocating sensitive equipment away from harmonic-heavy circuits can resolve performance issues without requiring major system changes.
Zig-Zag Transformers
Zig-zag transformers provide a low-impedance path for zero-sequence currents, helping to cancel out triplen harmonics, especially the problematic third harmonic, on the neutral and prevent overloaded neutral conductors. This can significantly reduce neutral current and the associated heating in systems with heavy nonlinear loads.
Phase Shifting
Phase shifting involves using transformers with different phase angles (like 0° and 30° phase shift) to feed multiple rectifier loads. This technique spreads harmonic currents across phases in a way that causes them to cancel each other out on the upstream system. When properly implemented, phase shifting can dramatically lower the THD found at the main service entrance.
Preventive Practices for the Future
Facilities should adopt preventive practices beyond one-time troubleshooting to maintain power quality and protect sensitive equipment. Continuous harmonic monitoring is key to detecting changes in system behavior over time, especially as load profiles shift or new equipment is added. Regularly reviewing this data can aid in identifying emerging harmonic issues before they lead to costly downtime or equipment damage.
When commissioning new power delivery systems, it’s essential to verify that components, such as inverters, meet the performance criteria outlined in project specifications and that the incoming utility power quality aligns with manufacturer requirements. Including harmonic checks in this process ensures both installed systems and external sources are held to the correct standards. This documentation can help prevent future disputes by clearly identifying whether power quality issues originate from the facility or the utility, avoiding costly legal conflicts over liability.
Tools like Fluke Connect make logging and archiving power quality data easier, providing a traceable record that supports compliance, troubleshooting, and long-term system reliability. With Fluke Connect, users in the field can also share live measurements with colleagues and upload screenshots of the measurements to a cloud location for easy access from anywhere in the world.
About the Author
Jason is a subject matter expert at Fluke specializing in power quality, electrical test equipment, and product applications. With deep experience supporting both customers and distribution partners, he helps professionals select, operate, and troubleshoot a wide range of diagnostic tools—including power quality analyzers, battery testers, acoustic imagers, and thermal imagers. Jason regularly leads application-based training sessions, drawing on his hands-on knowledge to bridge the gap between technical challenges and practical solutions across industries. Connect with Jason on LinkedIn.