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www.sname.org/sname/mt July 2013 Further, beyond the limited-scale testing at RITE, the clear commercial potential for this MHK technology is at larger per- turbine scales and power levels at deeper sites with faster ows. Accordingly, another (related) criterion for this development has been scalability, and we have preliminarily extended the basic Gen5 design to systems of at least 10 m diameters and 250 kW per unit. Gen5 KHPS design e Gen5 KHPS design builds upon the lessons learned from the fabrication and in-water operation of the previous generation sys- tems. ere are two fundamental di erences between the Gen4 and Gen5. First, unlike the Gen4 design, which relied as much as pos- sible on o -the-shelf components, the Gen5 turbine has been designed based on custom components and designs and materi- als better suited to volume production. is has enabled dramatic mechanical integration and parts count reduction, as well as closer tailoring of the design to the environment, such as redun- dant sealing. Enhanced reliability and longevity have been the result, along with cost reduction. Second, the Gen5 turbine incorporates a failsafe? brake. is spring-applied electrically-released brake protects the rotor, drive- train, and structure from overloads, and reduces wear. It also enables installation safety improvements. is change further entailed a sig- ni cant update of system control hardware and strategy. Rotor development To meet the requirements of longevity and scalability, in terms of strength and corrosion-resistance, an entirely new composite rotor blade was developed for the Gen5 KHPS. We were assisted in this work by the National Renewable Energy Laboratory (NREL) and Sandia National Labs under cooperative research agreements. In addition, a DOE Advanced Water Power Program award permit- ted further analysis by the University of Minnesota St. Anthony Falls Laboratory, and the fabrication of blades and testing of the new rotor at full scale in the lab at NREL and in the water at RITE in 2012. As before, the rotor blades are non-pitching, and have to perform well in a range of water speeds into a near- xed speed load. An all-composite blade was designed to be mounted to a cast ductile iron hub. is new design had to improve upon the structural capabilities of the prior blade and enable economical volume berglass fabrication, while not sacri cing the previous e ciency. Extensive modelling and analysis were performed using multiple modi ed wind turbine codes on both the Gen4 design and evolving Gen5 designs. A further constraint was avoid- ance of cavitation, and a novel design methodology was used, resulting in a signi cant improvement. e blade designs were subjected to multiple independent computational uid dynamics analyses, and ultimately the full rotor and turbine. e performance results also were compared with empirical Gen4 data from RITE in-water dynamometry. e blade and its mounting component designs were also ana- lyzed for static and fatigue stresses under the speci ed loads. e fabrication methodology for the new blade has been carefully coor- dinated throughout the design process to ensure an economical manufacturing process for initially low-volume, but increasing to high-volume production. Our blade fabrication partner, Energtx Composites of Holland, Michigan, was able to meet the initial costs and has the potential for achieving further cost reductions through evolving methodologies and volume production. Turbine design As described earlier, the Gen5 is a ground-up design with regard to the use of custom components designed to optimize per- formance and reliability, and to provide economical volume production. Key Gen5 enhancements include: ? composite (epoxy berglass) blades ? cast iron hub and nacelle/pylon connection ? integrated extreme-life drivetrain, including gearbox, shaft housing, bearings, lubrication, and seals ? redundant dynamic (shaft) and static sealing ? customized environmentally capable generator ? failsafe brake ? utility-grade data acquisition and control and supervisory control ? non-toxic fouling-release coating system ? manufacturing under a quality management system. Several structural elements have been simpli ed and reduced in cost for volume production by replacing steel weldments with ductile iron castings. ese include the rotor hub and the pylon to nacelle joint. Indeed, the main central nacelle section is a sin- gle casting that replaces a weldment of a steel tube and milled ange. Further, various minor components have been simpli ed. e main drivetrain components of shaft, bearings, and gear- ing, along with the mechanical dynamic shaft sealing has been re-developed as a single integrated whole, drastically reducing the parts count and enabling improved geometry and cost-e ective assembly. It also has permitted incorporating several ultra-reliability features designed to enable extended service intervals for the pecu- liar requirements of this kinetic hydropower service, including those related to gear and bearing lubrication and sealing. e new generator is customized with regard to materials, treatments, and seals for added protection in our application. e failsafe brake and associated electrical sensors and controls have been selected and implemented for maximum reliability,