This paper describes the design and performance of a 10kW partially superconducting homopolar dc generator with an ambient temperature rotor on the Faraday disc principle and with the field supplied by a stationary superconducting coil. This configuration of machine could, in very large ratings, compete with conventional machines. A simple solenoid field coil is wound with a fully stabilized Nb-Ti composite wire and produces a central field of 40kG. The inner dia., outer dia., and length of the coil are 21.5, 34, and 25cm, respectively. The disc type rotor consists of 8 copper discs of 13cm diameter connected electrically in series by the inner and outer brushes and its overall length is 50cm. The maximum output power of the generator was obtained 10V-1, 000A-10kW and the current density of a brush was up to 100A/cm2, which was five times as high as that of conventional machines.
The large superconducting magnet may be usually cooled down by a large amounts of liquid helium. But its procedure is not considered as the best way for cooling down method. We have established the direct cooling method for small superconducting magnet by the use of external remote delivery tube. And by the way for combining the liquefier with the specially designed long transfer tube. We succeeded to cool-down the large saddle-type superconducting magnet.
The effects of the cooling perimeter on the terminal voltage-current characteristics were investigated for various superconducting strips. When the critical current was higher than the recovery current and when the adhesion between superconducting wires and copper substrate was poor, then the current carrying capacity and the recovery current were found to degrate with decreasing the magnitude of the cooling perimeter. Particularly in case of zero cooling perimeter, the equivalent heat flux obtained was not zero, but of a finite value. This may be thought to be due to the longitudinal thermal conduction in the conductor. Many small voltage jumps, like a step, were often observed in the terminal voltage vs current curves, which was mainly due to the irregularities of the critical current of each wire embedded in the copper substrate and to those of the surface resistance between wires and copper substrate.
Experiments of boiling heat transfer to liquid helium is described. Variation of critical heat flux qc with gap width and distance from inlet of cooling channel was measured. The gap widths of vertical channels, of rectangular cross section, were 1, 2, 3, 4, 5mm and open. The lengths of the channels were 5, 10, 20 and 40cm. Comparison of our experimental results with the data obtained by Wilson and Lehongre showed good agreement. By using simple assumptions, mechanism of heat transfer in channels was analysed qualitatively. Also the results in the case of inclined channel are presented.