Dynamic positioning power plant system reliability and design

Power plant reliability is critical for the operation of dynamic positioning vessels. There are several common-mode failures of the engine, synchronous machine, governor, and exciter system that can cause a complete blackout of the on-board power system and millions of dollars in revenue loss. Closed bus-tie operation of power plants provides superior tolerance for dynamic positioning power plant faults. However, a vessel operating with closed bus-tie breakers is not guaranteed to retain thrusters during certain types of power system failures. In these situations, rapid recovery of equipment is critical for meeting the minimum requirements of station keeping. Open bus ties are often used when rapid recovery is inadequate to meet operational needs and retention of thrusters is necessary. Operating with open bus ties reduces overall power plant reliability but maintains the availability of thrusters during any equipment fault. This paper presents a design that provides the desired reliability of closed bus-tie operation, while providing nearly the same thruster retention capability as open bus-tie operation. Using advanced fault detection and plant management techniques, faults that typically result in the loss of all thrusters on a closed bus-tie power plant can be handled such that sufficient thrusters remain operational to continue dynamic positioning operation, even after the fault. This paper explains several critical protection areas for offshore vessel failure modes currently affecting these vessels and concludes with a design discussion of the latest technology in the area of protection and control.