Industrial accident: Performance of a 12 cell battery pack in a subsea control system during the BP Macondo / Transocean Deepwater Horizon Oil Spill. The forensic issues included the battery's ability to deliver specific levels of current and voltage at various depletion levels. The testing conducted by DNV was preformed at both normal and subsea temperatures.
The packs were used individually to provide a nominal 9 volts, and with three in series to provide 27 volts. The analysis of forensic testing included the individual lithium cells as well as the effects of the pack's internal components. The power loss of diodes, thermal cutoff protection, and polyswitch overcurrent protection. were evaluated at various operating conditions.
Further analysis was done to evaluate the approximate battery state during the accident based on voltage and current testing done after recovery of the BOP control pods. The investigation analyzed the ampacity curves for the lithium cells when subjected to various load levels at several stages of cell depletion.
Additional investigation was done in regard to the use of primary (non-rechargeable) and secondary (rechargeable) batteries in the BOP control system. The Mark II control system did not use rechargeable batteries, and had no ability to monitor the battery condition on the seafloor. Subsequent BOP control system designs provided both rechargeable batteries as well as online battery monitoring.
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