Proceedings of OMAE 2004: 23rd International Conference on Offshore Mechanics and Arctic Engineering 20-25 June 2004 Vancouver, Canada OMAE2004-51213 CONVERTING KINETIC ENERGY IN SMALL WATERCOURSES USING DIRECT DRIVE GENERATORS Karin Nilsson 1 Email: karin.nilsson@hvi.uu.se Erik Segergren 1 Email: erik.segergren@hvi.uu.se Jan Sundberg 1 Email: jan.sundberg@hvi.uu.se Elisabeth Sjöstedt 1 Email: elisabeth.sjostedt@hvi.uu.se Mats Leijon 1 Email: mats.leijon@hvi.uu.se 1 Uppsala University, Department of Engineering Science Box 534, SE-751 21 Uppsala, Sweden ABSTRACT Tidal currents, ocean currents and unregulated watercourses are all large sources of energy that can be converted into electricity. Several technical and economical solutions within this research area have been demonstrated. In literature there exists two different turbine types, horizontal and vertical axis. The present paper focuses on the design of a permanent magnetized generator directly coupled to a vertical axis turbine. The proposed theoretical concept is adapted to data measurements regarding water current velocities and flow profiles from a Swedish watercourse. A high electromagnetic efficiency of 90 % is obtained. Keywords: current power, direct drive generator, permanent magnetized, vertical axis turbine INTRODUCTION One of the difficulties in electric conversion from unregulated watercourses is an economical use of the natural variations of the flow velocities. Most systems for converting energy from marine currents use a conventional high-speed generator including a gearbox between the turbine and the generator [1-6]. However, due to its moving parts, a gearbox is a weak part of the system, associated with a frequent need for maintenance. Since the maintenance costs increases drastically once the device is placed under water, the number of components and moving parts should be reduced to a minimum. A system with a direct drive generator reduces the number of components considerably and thus prolongs the intervals between maintenance. However, a directly coupled generator will have a very low rotation speed and a varying frequency, determined by the natural movement of the water current. Rectifying the output current solves this problem. Extensive overloads are difficult to handle with mechanical solutions, but a direct drive generator can be designed to handle these overloads electrically. Besides, turbine load variations can be converted into electricity with high efficiency. A further way to simplify the construction is to use permanent magnets in the rotor, since no electric coupling to the rotor will be needed [7]. One of the major environmental issues for hydroelectric power production is mortality of turbine passed fish and it is a major environmental goal to increase the survival of downstream-migrating fish at hydroelectric dams [8]. The concept proposed in this paper has promising advantages in this area. Compared to conventional hydropower plants, where large proportions of the migrating salmonids passing a turbine are killed [9], the fish mortality is expected to be nearly zero at a current power plant. For Swedish conditions the main interest in this research area is the possibility to use renewable kinetic energy in unregulated or partly regulated watercourses. The suggested concept allows a construction without noise and visual disturbances and corresponds well with the effort to minimize the environmental and ecological impact. In this paper a permanent magnetized generator is adjusted to the flow velocities in a partly regulated watercourse (measurements performed by the Swedish Meteorological and Hydrological Institute, SMHI). The design of the generator is 1 Copyright © 2004 by ASME