Battery storage container destroyed by fire during commissioning at Perles-et-Castelet substation

During acceptance testing of a newly installed hybrid battery and supercapacitor storage unit at the Perles-et-Castelet RTE transformer substation in Perles-et-Castelet, Ariège, France, operated and owned by RTE, with the storage system supplied by Ingeteam as manufacturer and integrator, temperature and smoke alarms activated shortly after the equipment was energised. Personnel evacuated the control room as smoke emerged from one of two stacked containers. Around 45 minutes later, an overpressure event blew open the container doors and a fire broke out, ultimately destroying the storage container despite an extended firefighting response. Investigation established that one battery rack suddenly discharged into an adjacent rack, with the resulting current flowing only through part of the second rack. Insulation resistance in the first rack had fallen close to short-circuit levels. Investigators proposed that a failed electrical connection contacting the rack's metal frame, combined with an insulation fault on a busbar linking a module to its protection unit, may have caused an electric arc upstream of a fuse.

Investigators identified a probable insulation fault at electrical connections passing through the battery rack support frame, potentially combined with a failed electrical connection contacting the metal frame, which may have produced an electric arc not cleared by the fuse protection. The precise root cause of the insulation fault itself could not be determined.

1. Verify that all critical measurement functions are recorded and stored remotely so that post-incident data is not lost with the damaged equipment.
2. Give particular attention to the design and inspection of electrical connections that pass through metal rack frames, since chafing or contact faults in these locations are difficult to detect.
3. Implement automated, continuous monitoring of insulation resistance at both rack and module level rather than relying on periodic checks.
4. Ensure electrical protection devices are sized and coordinated to reliably interrupt fault currents arising from internal rack-to-rack faults.
5. Review the sizing of fire extinguishing systems and the feasibility of rapidly isolating energy supply during commissioning tests, when protective systems may not yet be fully proven.

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