"ScienceAlert is reporting that researchers may have finally determined why, for many years, power grids around the world have been pulsing every 60 seconds," writes longtime Slashdot reader fahrbot-bot. The likely culprit? Uninterruptible power supplies running routine battery checks. From the report: Every minute, some uninterruptible power supplies perform routine battery checks, creating small but measurable surges in electricity demand. And it's like clockwork. "Even benign control routines can become systemically relevant when many devices act coherently," writes a team led by physicist Dirk Witthaut of the University of Cologne, Germany, in a paper published in Nature Energy. "Unintended synchronization can generate recurrent and potentially amplified oscillatory behavior in large-scale cyber-physical energy systems." To figure it out, Witthaut and his colleagues analyzed high-resolution electricity measurements from buildings at the Forschungszentrum Julich research campus in Germany. [... they found that] the 60-second pattern appeared in four buildings, all of which contained uninterruptible power supplies. None of the buildings they measured without these systems showed the same pattern. Following the electrical signals more closely, the researchers detected tiny bursts of current from the batteries at precisely one-minute intervals. They were able to trace the resulting fluctuations through one building's electrical system, all the way to the connection with the public high-voltage grid. The manufacturer subsequently confirmed the culprit's identity -- routine battery self-tests, conducted automatically by the systems' management software. But why would equipment in different buildings, let alone different countries, be doing this at the same time? The answer appears to lie in the clocks. Digital devices can synchronize their internal clocks using external time signals, meaning that independently operating systems can end up performing their scheduled tasks together. Individually, these small checks are insignificant. But when enough devices act in synchrony, their combined electricity demand can produce a measurable effect across an entire power grid.

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