Dublin Utility: Power Outage Not Caused by Lightning Strike

The local power company in Dublin, Ireland now says a lighting strike was not the cause of the utility power outage that triggered downtime for major data centers operated by Amazon and Microsoft. The Electricity Supply Board (ESB) said the outage remained under investigation, but was caused by an equipment failure rather than lightning.

The power company issued its statement after readers in the comments of our post and in other media outlets raised questions  about the utility's initial finding that lightning caused the outages -  an explanation which Amazon and Microsoft then shared in status updates for users and media.

ESB Networks confirms that it suffered a failure in a 110kV transformer in City West, Dublin at 6:16 p.m. local time on Sunday, August 7. "The cause of this failure is still being investigated at this time but our initial assessment of lightning as the cause has now been ruled out," EBS Networks said in a statement. "This initial supply disruption lasted for approximately 1 hour as ESB Networks worked to restore supply. There was an ongoing partial outage in the area until 11pm.  The interruption affected about 100 customers in the Citywest area, including Amazon and a number of other data centres.  Another Amazon data centre served by ESB in South County Dublin was not directly affected by the outage, though it did experience a voltage dip which lasted for less than one second.”

The one-second voltage dip had been cited in a separate media report which added to the confusion about Sunday's events.

ESB made it clear that in referencing a lightning strike, Amazon was sharing its best information at the time.

"Amazon accurately reported the information which had been passed to them from workers at the site," said Marguerite Sayers, Head of Asset Management at ESB Networks. "Both the explosion and fire were localized to the bushings or insulators of the transformer and did not require the attendance of the emergency services. The extent of associated internal damage to the transformer was serious and resulted in supply interruption to a number of customers, and also impacted Amazon’s systems, as they have reported."

Advanced data centers like the Amazon and Microsoft facilities usually continue operating through utility outages, relying on backup diesel generators to supply power. Both companies have said that fluctuations in the incoming utility power interfered with its automated systems to start backup generators once the power failed.

"When the transformer failed, there was a voltage dip experienced by customers in parts of Dublin for the duration of the fault," Sayers said, who said she couldn't comment on individual customers' UPS or standby generator performance. "However, I can certainly confirm that this was an unexpected fault situation, with absolutely no advance warning, which did result in a voltage dip for many customers, in addition to supply loss for approximately 100 customers."