The article gives general aspects of superconducting alternator, which is noticed as an application of superconductivity on electrical machine recently. A careful consideration is required to design the machine composed of some unique parts. Electrical characteristics of superconducting machine have been found considerably different from conventional machines owing to lack of iron core. Mainly, superconducting alternator has been considered to be useful as large turbo-generator for central power station, but it is expected to be useful as electrical ship propulsion system and as synchronous condensor also. Finally, present status of development is reviewed.
This paper is a review tracing the development of superconductive communication cables. A 1.6mm superconductive coaxial line constructed of Pb conductors and FEP dielectric has been developed, which has the characteristic impedance of 50±0.3 ohms and the attenuation of about 0.6dB/Km at 1GHz and 4.2K. The attenuation up to 4GHz is mainly due to dielectric losses. Superconductive coaxial lines are arranged in a helium conducting tube and refrigerated by liquid helium. The helium tube is insulated thermally from room temperature environment by multilayer insulators, shield conductors and vacuum space. At present, the total heat inflow into cryogen in the refrigerant conductor is about 100W/Km.
A. c. losses of superconducting solenoidal coils are measured by calorimetric method under applying uniform a. c. magnetic field or flowing through a. c. current to them. The circular cross-sectional wires, which have five sorts of copper ratio over a range from 2.1 to 8.3, are composed of twisted 271 filaments of Nb-Ti-Zr 50μ in diameter embedded in a matrix of low resistivity copper. The range of applied a. c. currents is 0-15 rmsA and magnetic field 0-200 Oe, at 50Hz. In these conditions, the observed a. c. losses result from eddy current losses due to “proximity effect” and are proportional to the square of magnetic field or current. The a. c. losses in the fine multifilamentary superconducting wires decrease in about 1/4 of those in the pure copper wires with the same diameter as them. The losses of solenoidal coils can be calculated by introducing a mean magnetic field in the winding and a numerical constant to the eddy current loss formula, whether both ends of coils are open or close and the magnetic field is an applied field or self field.
Heavily doped n-type GaAs, whose carrier concentration is about 1×1018cm-3, exhibits magnetic-field-independent and temperature-insensitive Hall coefficient up to 100kG and 100°C. Since such characteristics are excellent at liquid helium temperatures, Hall element prepared from this material is especially useful for superconducting magnet. A convenient digital gaussmeter employing this Hall element is confirmed, by means of NMR calibration, to indicate the exact response at 1mV/10kG and the resolution down to ±10G.