German transmission company E.On Netz has disclosed that human error at a control centre was behind the cascading power outage that plunged large swathes of Europe into darkness on 4 November.

According to the latest findings of the company’s in-house investigation into the causes for the disruption, “human error, as opposed to any technical malfunctions, was chiefly responsible.”

The results of a detailed reconstruct of the chain of events that led to the disruption reveal that “an E.On control centre had assessed developments correctly… but, owing to time pressure, had not made use of all technical options for a comprehensive situation analysis.” The centre had not checked whether the outage of an additional transmission line might overload the power grid when assessing the risks associated with switching off a power lines to allow a ship’s passage along the River Ems. About half an hour later, another high voltage transmission line was overloaded – for reasons that are not yet known. To compensate for this, a number of lines were switched together at a substation and, contrary to the assessment of the control centre staff, this did not decrease but further increased the load on the power grid, which, in turn, triggered an automatic shutdown procedure.

The preliminary results of the UCTE investigation into the incident are due to be released in the next few days.

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