Late on March 20, 2025, a transformer fire at the 275kV North Hyde substation in west London knocked out the entire station. Heathrow — Europe’s busiest airport — closed for nearly a full day, disrupting over 270,000 passenger journeys; 66,919 customers lost power, hospitals were affected, three data centers ran on backup generation, and nearby residents were evacuated overnight.
The UK National Energy System Operator’s final report revealed a startling truth: the fire stemmed from a catastrophic failure of a high-voltage bushing — moisture ingress triggered an electrical fault, short circuit, and ignition of insulating oil. Crucially, elevated moisture had already been detected in oil samples back in July 2018, but no proportionate action followed, and basic maintenance scheduled for 2022 was deferred.
In other words, the warning came seven years before the incident. A moisture-compromised bushing is a textbook scenario for insulation degradation and partial discharge — degrading insulation typically “makes noise” through sustained PD activity before breakdown. PD testing and trend tracking on that bushing, with data-driven replacement prioritization, would very likely have prevented the event. Heathrow’s lesson for every asset manager: detecting an anomaly is only step one — predictive maintenance only works when monitoring data becomes action.
Wintech Electric’s PD testing and online monitoring solutions help utilities catch bushing and transformer insulation degradation before it becomes a disaster.
