Simultaneous faults on the 11 kV system of an offshore FPSO vessel

This paper provides a case study of simultaneous faults that occurred December 5, 2009, within the 11 kV power system of a floating production, storage, and offloading vessel located in the Norwegian sector of the North Sea. The event resulted in severe damage to a 9.2 MW compressor drive motor, damage to the transformer feeding an adjustable speed drive, and interruption of many loads on the ship. Background regarding the power system on the vessel and the state of the system at the time of the event is provided in Section I and Section II. This paper shares an exhaustive analysis of the event, including initial responses and findings of the offshore technicians, event reports from two microprocessor-based motor protection relays, subsequent analytical work, and forensic work performed on the failed equipment. This paper highlights the importance of event analysis, including the value of time-aligned event reports from devices throughout a power system. Modeling of simultaneous faults, zero-sequence sources, and faults at the neutral point of an ungrounded-wye induction machine are also discussed. This paper shares the lessons learned as a result of the event, including proposed improvements to the protection system.