<p>For more than a decade, power grids separated by great distances have shown a tiny, unusually regular change in electrical frequency every 60 seconds. A ScienceAlert report by Michelle Starr describes a study that traces the pulse to routine battery checks in uninterruptible power supplies, or UPS units—the backup systems used in places such as hospitals, data centers and research facilities.</p><p>The proposed explanation is that many devices may be doing the same small task at nearly the same moment. Their individual power demands are minor, but if they line up, their combined effect can be measured across a grid. The researchers say the explanation still needs testing in other locations.</p><p>Electricity grids must constantly balance production with consumption. When demand briefly exceeds supply, grid frequency falls; when supply exceeds demand, it rises. Small, irregular fluctuations are normal. What caught researchers’ attention was a pulse recurring with striking precision across grids that are not physically connected.</p><p>Earlier observations had linked minute-scale fluctuations to hydropower, but that could not account for similar patterns reported in grids with different configurations, including in continental Europe, Britain, Australia and the United States. The report describes evidence from grids on five continents, including physically isolated systems.</p><p>To investigate the cause, a team led by physicist Dirk Witthaut of the University of Cologne analyzed high-resolution electricity measurements from buildings at the Forschungszentrum Jülich research campus in Germany. The minute-long pattern appeared in four measured buildings that had UPS units; it did not appear in the measured buildings without them. In one building, researchers traced the electrical fluctuations through the building’s wiring to its connection with the public high-voltage grid.</p><p>They also detected small bursts of current from the UPS batteries at one-minute intervals. According to the report, the manufacturer confirmed that the systems’ management software automatically ran routine battery self-tests. External time signals can synchronize digital devices’ internal clocks, the researchers suggest, so systems operating independently may nevertheless schedule checks together.</p><p>The distinction matters: the report presents evidence for a mechanism found in campus buildings, while its explanation for a pattern seen across distant grids remains to be confirmed elsewhere. Researchers say the observed fluctuations currently pose no immediate threat to grid stability and are typically only a few millihertz in amplitude. They also warn that grid dynamics can amplify small oscillations, potentially adding wear to equipment such as hydropower turbines.</p><p>As digitally controlled equipment, battery storage and data centers become more common, synchronized demand could become more significant, the researchers caution. One possible way to reduce the effect is to vary device schedules so that large numbers of systems do not run checks at exactly the same time. The report says one manufacturer issued a software update that relaxed the strict timing of checks on a system the researchers had identified.</p><p>The work was published in <i>Nature Energy</i>. Source: ScienceAlert report.</p>