Fire that led to Heathrow shutdown caused by issue detected years ago
The substation fire that led to Heathrow being shut down on 20 March was caused by an issue detected years ago that was never appropriately addressed.
This is according to the final report into the outage at the North Hyde Substation published by the National Energy System Operator (NESO).
NESO found that the outage was caused by a ‘catastrophic failure’ of one of the substation’s transformers which caused it to catch fire. This failure was most likely caused by moisture entering a high-voltage bushing, causing an electrical fault.
Importantly, oil samples taken in July 2018 at the substation found an elevated moisture reading in the bushing, but appropriate actions were never taken to mitigate the problem.
Following this discovery, National Grid Electricity Transmission has initiated an end-to-end review of its oil sampling process and all recorded oil samples to ensure appropriate actions have been taken where required.
The review also found that the configuration of Heathrow Airport’s private internal electrical distribution network meant that the loss of one of its three independent supply points would result in the loss of power to some of the airport’s operationally critical systems.
To address this, Heathrow Airport reconfigured its internal electrical distribution network to take power from the other two supply points upon failure of the substation. The process to enact this is estimated to take 10-12 hours, a timeframe which was not known to energy companies.
As a result of the substation fire, Heathrow closed for most of 21 March so that its internal network could be reconfigured to take power from the two other supply points and to perform safety checks. The airport reopened for some flights late on 21 March and was fully operational from 22 March.
NESO noted that the impacts of the substation fire beyond Heathrow Airport were significant, affecting nearby essential services including hospitals, road, and rail infrastructure, as well as thousands of homes and businesses.
“The power outage and closure of Heathrow airport were hugely disruptive and our report seeks to improve the way parties plan for and respond to these incidents, building on the underlying resilience of our energy system,” said NESO Chief Executive Officer Fintan Slye.
“NESO’s final report into the North Hyde Substation outage sets out the root cause and a clear set of recommendations to further improve the resilience of Great Britain’s energy system, and the resilience of its critical national infrastructure.”
“All parties involved are focussed on working together to deliver these important recommendations and much of this work is already underway with NESO’s full support,” Slye said.
