This paper proposes a new type of machine, in which two-stage runners counter-drive, respectively, the outer and the inner rotors of a generator without the usual stator, and discusses performances and internal flow conditions of the model machine. The maximum output power is obtained at the same counter-rotational speeds as expected in the design. Such a machine is suitable for boarding on a floating buoy supplied for the tidal current power generation, because the rotational torques of the machine are counter-balanced themselves. The desirable profile of the buoy is also investigated.
To cope with the warming global environment, the hydropower should occupy the attention of the electric power generation system as clean and cool energy sources. In such a situation, the tidal current has scarcely been utilized for the power generation, for instance, the Kanmon Straits in Japan has about 54 MW hydraulic energy. It may be suitable, for the tidal current power generation, to apply the high specific speed hydroturbine such as usual axial-flow types, cross-flow types (Toyokura et al.,1990) and/or Darrieus types (Furukawa et al, 1998). It is also desirable to make the machine compact size and simple composition, but the usual generator may reject such desires. That is, it is necessary, for getting sufficiently the electric power, to make the rotor diameter large or equip with the accelerator such as a gear-box, because the electric power is in proportion to the rotational speed in the magnetic field. Therefore, the authors have proposed and developed a new type of generator with counterrotating rotors instead of the usual mechanism, which can make the generator diameter small on account of relatively double the rotational speed.
