The fire that destroyed two Tesla Megapacks among the 212 units that make up the Victorian Big Battery was caused by coinciding short circuits in two locations, according to an investigation by Energy Safe Victoria

The fire in late July most likely resulted after a cooling system leak caused a short circuit in an electrical component in a Megapack.

These events occurred while the Megapack was off-line in a service mode, which meant that fault protections were removed and the problem was able to go undetected. This resulted in heating that led to a thermal runaway and fire in an adjacent battery compartment within one Megapack, which spread to a second Megapack.

Chain of events

An independent report into the fire will be released by November but Energy Safe Victoria has pointed to contributing factors that, had they not been present, “would likely have been identified and either manually or automatically contained”.

• The supervisory control and data acquisition (SCADA) system for a Megapack took 24 hours to ‘map’ to the control system and provide full data functionality and oversight to operators. The Megapack that caught fire had been in service for 13 hours before being switched into an off-line mode when it was no longer required as part of the commissioning process. This prevented the receipt of alarms at the control facility.
• A key lock was operated correctly to switch the Megapack to off-line service mode (which was no longer required for ongoing commissioning) but this caused:
  • telemetry systems for monitoring the condition of the (now out of service) Megapack to shut down and so remove visibility of the developing event
  • the battery cooling system to shut down
  • the battery protection system to shut down, including the high voltage controller (HVC) that could have operated a pyrotechnic fuse to disconnect the faulty battery unit.

Prevention

The findings were informed by testing undertaken by Tesla, examination of the scene by ESV (and other Victorian agencies), video and telemetry data from the original incident.

Energy Safe Victoria has required additional safety measures, including: Megapack cooling systems are fully pressure tested when installed on site; Megapack cooling systems are inspected for leaks after testing; shorter connection times to the SCADA system to help alert Tesla with specific alarms; a new battery module isolation loss alarm has been added, and; procedure changes for Megapack protection systems.

Designers are also working to ensure that Megapacks are engineered to fully mitigate the risk of fire propagation from one unit to another under Victorian climatic conditions.

Energy Safe Victoria requires Tesla to provide the final results of its investigation into why the fire resulted in the loss of a second Megapack and what it is to do to prevent that circumstance arising again. It will now determine if there have been any breaches of the Electricity Safety Act 1998 (Vic) and supporting regulations and, if so, whether enforcement action is warranted.

Testing to restart

The 300MW/450MWh Victorian Big Battery, under construction at Moorabool near Geelong, is one of the world’s largest battery storage projects and will unlock up to 250MW of additional peak capacity for Victoria.

Project owner Neoen will restart testing of the battery on Wednesday September 29. If all goes well, it hopes to be providing services to the grid through another hot Victorian summer.

Neoen’s 193MWh Hornsdale Power Reserve has been operating in South Australia since it was commissioned in December 2017. It was expanded from 129MWh late last year.

Energy Safe Victoria is the state’s safety regulator for electricity, gas and pipelines and is responsible for licensing and registering electricians. It delivered its findings following an almost two-month investigation, analysing data from Neoen and contractors UGL and Tesla.