Pollution
Humain
Environnement
Economique

A 63 kV/20 kV transformer caught fire at around 12:20 p.m. at a wire factory that had been shut down for two months. Two 63 kV lines led to a high voltage busbar that could be remotely controlled by the electric utility company. The remote control system worked only if the operator’s 20 kV network was online. The transformer and 63 kV network were located outdoors. The operator’s 20 kV network led to a building containing capacitor batteries, connectors, control devices, and the alarm management system.

Complicated response efforts

The failure of the 20 kV network prevented the electric utility cutting the current on the busbar and forced it to cut the electricity supplying the 63 kV line well upstream of the factory. However, the electricity supply of a Seveso plant co-supplied by the same line cannot suddenly be cut off. The utility therefore waited for two hours so that the machinery at the nearby Seveso plant could be safely shut down before cutting off the electricity supply. This cut in power did not appear to have had an impact on the nearby plant.

However, it caused the safety equipment (alarm, sprinklers) at the wire factory to malfunction despite the fact that chemicals storages were still at the factory. The overheating of the transformer caused it to spill its oil. The soil around the transformer was excavated. The resulting damage amounted to several thousand euros.

The accident’s causes are yet to be determined

While maintenance was being carried out on one of the factory’s transformers, the 20 kV network may have short-circuited and caused the 63 kV/20 kV transformer to overheat, in turn overheating its cooling oil and raising its internal pressure. This pressure may have then been vented by the transformer’s valve, spraying out oil in the process.

Measures taken by the operator

While the electricity supply was being restored, a security firm conducted rounds to look for a three-phase diesel generator to power the boiler, the computer and telephone systems, and the guardhouse’s alarms and equipment.