Transformer fire at Blount Street substation causes Madison, Wisconsin outage

In July 2019, a transformer at American Transmission's Blount Street substation on East Main Street in downtown Madison, Wisconsin, failed, resulting in an explosion and fire. Insulating fluid burned in the fire, producing a thick smoke column visible over a wide area. Shortly after the fire began, the local distribution utility de-energised the substation to allow firefighters access, which interrupted supply to downtown Madison customers. Distribution crews worked through the day and all affected customers were reported reconnected by early evening. Transmission equipment at the connected East Campus substation was also damaged, although the distribution utility's equipment at that site was reported undamaged. The Wisconsin state environmental regulator supervised cleanup of the Blount Street site. Some insulating fluid burned in the fire, the remainder was pumped from the transformer over the following weekend, and an environmental contractor used a skimming method to separate dielectric fluid from firewater that had flowed from the substation. American Transmission stated publicly that the fluid was a dielectric fluid commonly used for insulating electrical equipment, and the environmental regulator confirmed that it did not contain PCBs.

Publicly reported information was limited. American Transmission stated that a transformer failure had occurred and that it was examining the transformer components to identify the root cause. No root cause was published at the time of reporting. The reported burning and release of dielectric fluid is consistent with loss of containment from the transformer, although the failure mechanism was not published.

1. Transformer fires at substations in built up areas produce visible smoke, road closures and public safety concern in addition to the customer outage, so prepare public communication and stakeholder notification protocols before an event.
2. Burning dielectric fluid and contaminated firewater create an environmental response obligation, so establish contact routes and expectations with the environmental regulator and a retained environmental contractor in advance.
3. Confirming the composition of insulating fluid, including whether it contains PCBs, is an early information need during emergency response, so hold current fluid documentation for each transformer in a form that can be released quickly, particularly for older units.
4. De-energisation to allow firefighter access requires coordination between the transmission asset owner and the local distribution operator, so document the switching sequence and the interface responsibilities in joint emergency plans and test them.
5. Design site drainage and bunding so that firewater and released fluid are captured for controlled disposal rather than discharged off site.
6. Damage to equipment at an electrically connected substation shows that consequences can extend beyond the site of the fire, so include propagation to adjacent and connected assets in substation fire risk assessments.
7. Same day restoration depends on prepared resources, so review spares holdings, crew availability and switching plans that allow supply to be restored by alternative routes while the damaged asset remains out of service.
8. Root cause analysis on a failed transformer requires component examination, oil sampling and internal inspection, so plan for an extended investigation period in remediation and reporting programmes.

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