Coordinated disturbances haunt grids worldwide. Here’s how researchers solved the mystery.

For decades, an enigmatic electrical anomaly has baffled grid managers worldwide. These anomalies involve a periodic drop in the frequency of electrical grids, occurring precisely every 60 seconds across various countries and continents. German researcher Dirk Witthaut, from Forschungszentrum Jülich, was intrigued by this puzzle and embarked on a long investigation.

The phenomenon surfaced in Europe, Australia, the U.S., Malaysia, and other regions, all exhibiting the same pattern. Although such frequency drops are not unheard of, their regularity makes them increasingly worrisome.

Grid stability depends on maintaining a specific frequency range; large oscillations or unknown causes can lead to blackouts or equipment damage, particularly in hydropower turbines. Hydropower plants are usually the main drivers of these ultra-low frequency oscillations (UFLOs). Witthaut's team initially focused on hydropower, using a computer model of a hydropower plant control system on the Scandinavian grid to test their hypothesis.

They found conditions that could generate a resonance coinciding with the 60-second interval but couldn't explain why it persisted for such an extended period. This led them to suspect a clock, as anything operating with such precision would require one.

To test this hypothesis, Witthaut and his team installed smart power quality meters around the Forschungszentrum Jülich campus. These meters measured various parameters like frequency, voltage, current, and power every three seconds. They discovered that the transformer attached to a battery energy storage system peaked every minute, mirroring the grid's fluctuations.

Stationary batteries, including those in data centers and large-scale installations, check their state-of-charge every minute and are synchronized by internet connectivity. When these devices check their charge simultaneously, it creates a noticeable disruption on the grid.

Witthaut's team examined data from grid operators, which revealed that data centers in Ireland had grown to consume a substantial portion of the country's electricity. By 2022, data centers accounted for 18% of Ireland's grid load, with each facility supported by a fleet of UPSes. Frequency drops on Ireland's grid increased dramatically from 3 milli-Hertz (mHz) in 2016 to 12 mHz in 2021, and in some cases, exceeded 20 mHz.

Ireland's 50 Hz grid can tolerate swings of ±200 mHz, though operators prefer to keep them under 100 mHz.

To prevent such disruptions, the researchers recommend adding randomness to the schedule of UPS and grid-scale battery state-of-charge checks. Although these devices are the primary culprits, IoT devices like smart ovens and Raspberry Pi clusters can also introduce periodic fluctuations. Mitigating this issue might require software updates, but many IoT devices remain unpatched.

As the issue is global, it will likely require international cooperation. While the mystery has been solved, the problem persists, potentially for years.