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Thermal runaway root cause of Tesla megapack fires that shut down Australian ESS

Mon, 10/04/2021 - 09:29 -- paul Crompton

Thermal runaway in a Tesla megapack was the likely cause of a three-day fire that halted testing at Neoen’s 300MW/450MWh energy storage system (ESS) in Australia.

The fire at French firm Neoen’s Victorian Big Battery project occurred during initial testing of the ESS on 30 July and caused the system to be temporarily disconnected from the grid.

Two Megapacks (each being a shipping container-sized battery unit) were completely consumed by the fire. 

Neoen International SAS and its contractors UGL Engineering and Tesla Motors Australia), who respectively own and operate the site, have worked with safety regulator Energy Safe Victoria (ESV) throughout its investigation. 

Tesla’s engineering investigation and recreation of events found the most likely cause of the fire was a leak within the megapack cooling system, which caused a short circuit that led to a fire in an electronic component. 

This resulted in heating that led to a thermal runaway and fire in an adjacent battery compartment within one megapack, which spread to an adjacent second megapack. 

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

A number of other factors contributed to the destruction of the entire megapacks and, had they not been present, the initial fault would likely have been identified and either manually or automatically contained, said Neoen. 

Those factors are: 

  • 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.

ESV requires Tesla to provide the final results of its investigation (when available) into why the fire resulted in the loss of a second megapack and what it is to do to prevent that circumstance arising again. 

Having completed its technical review, ESV 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.

Back on line

Neoen confirmed re-energisation testing of the Victorian Big Battery would recommence on 29 September, in preparation for operations this Australian summer. 

Neoen and Tesla are continuing to work towards delivering the project in time for the Australian summer. 

The Victorian Big Battery will unlock up to 250MW of additional peak capacity on the existing Victoria/New South Wales Interconnector (VNI) over the next decade, playing a key role in the transition of the electricity sector towards lower emissions. 

ESV has advised Tesla that it has no objection to the recommencing of commissioning at the VBB providing a number of measures were installed.

The actions to prevent a recurrence of this incident are: 

  • Each Megapack cooling system is to be fully functionally and pressure tested when installed on site and before it is put into service 
  • Each Megapack cooling system in its entirety is to be physically inspected for leaks after it has been functionally and pressure tested on site 
  • The SCADA system has been modified such that it now ‘maps’ in one hour and this is to be verified before power flow is enabled to ensure real-time data is available to operators 
  • A new ‘battery module isolation loss’ alarm has been added to the firmware; this modification also automatically removes the battery module from service until the alarm is investigated 
  • Changes have been made to the procedure for the usage of the key lock for megapacks during commissioning and operation to ensure the telemetry system is operational 
  • The high voltage controller (HVC) that operates the pyrotechnic fuse remains in service when the key lock is isolated 

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, with proposed mitigation procedures to be rolled out to applicable megapacks globally.

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