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ACM completes investigation into power outage in Diemen

A combination of a technical failure and a human error at a high-voltage substation of transmission system operator TenneT near the town of Diemen (near Amsterdam) caused the large-scale power outage on 27 March 2015. Approximately one million households were left without power that morning. It affected a part of the province of Flevoland and a large part of the province of North-Holland. Rail traffic and air traffic were disrupted, hospitals had to cancel operations, and telephone systems broke down. It was only after an hour that power began to be restored gradually. This was concluded after an investigation that was conducted by an external consultancy commissioned by TenneT. The Netherlands Authority for Consumers and Markets (ACM) oversaw the depth and quality of the investigation. The results confirm TenneT’s earlier conclusions.

Two causes combined led to the power outage

The investigation revealed that a drive motor of a switch in the high-voltage substation malfunctioned. The switch was tested by a TenneT employee, but he made a misjudgement. This caused a short circuit. These two causes combined led to the power outage. ACM has not established a violation of the statutory requirements.

TenneT is making improvements

TenneT has made plans to prevent a repeat. Several improvements have already been carried out, especially in procedures and maintenance. The other improvements will be carried out by the end of 2017. ACM monitors the implementation of these improvements.