Root-Cause Analysis of Simultaneous Faults on an Offshore FPSO Vessel

The paper “Simultaneous Faults on the 11-kV System of an Offshore FPSO Vessel” by Haas provides a case study of simultaneous faults that occurred on December 5, 2009, on 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 12 000-hp compressor motor, damage to the transformer feeding an adjustable speed drive, and interruption of many loads on the ship. This paper shares analysis of the event, including initial responses and findings of the offshore technicians, event reports from two microprocessor-based protective relays, subsequent analytical work, and forensic work performed on the failed equipment. This paper includes additional analysis and forensic work that were not available at the time the previous paper on this event was published. Modeling of simultaneous faults, zero-sequence sources, and a fault 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. The importance of root-cause analysis in identifying problems before they result in significant damage is also discussed.