The discovery of high temperature oxide superconductors has stimulated us much interest in superconductivity applications to electric machines and apparatus again. Focused on the feasibility of such superconductors for electric rotating machines or motors, here are discussed perspectives and features of many sorts of electric motors such as to be available at present.
The Japan Atomic Energy Research Institute (JAERI) is conducting Demonstration Poloidal Coil (DPC) program for investigation of superconducting pulsed-coil technology for fusion. The DPC cryogenic system is designed to cool three forced-cooled superconducting coils being fabricated in this program and the system is composed of newly developed cryogenic circulation pump, cold compressor, and vapor-cooled current leads. The installation of these componets was completed in December of 1987 and the performance test of the whole system was carried out in March, 1988. In this test, we have demonstrated that the cryogenic system meets the specifications for cooling the coil system.
A new compact cryogenic cold compressor was developed by Japan Atomic Energy Research Institute (JAERI) in collaboration with Isikawajima-Harima Heavy Industries Co., Ltd. (IHI) in order to produce the supercritical helium below 4.2K for Demonstration Poloidal Coils (DPC) which are forced-flow cooled type superconducting pulse coils. This compressor is one of key components for DPC test facility. The cold compressor reduces pressure in liquid helium bath, which contains liquid helium of around 3, 000l, down to 0.5atm efficiently. Consequently, supercritical helium down to 3.5K is produced and supplied to the DPC coils. A centrifugal compressor with dynamic gas bearing is selected as a compressor mechanism to realize high adiabatic efficiency and large flow rate. In this performance tests, the compressor was operated for 220h at saturated condition from 0.5 to 1.0atm without any failure. High adiabatic efficiency (more than 60%) is achieved with wide flow range (25-65g/s) and the design value is fully satisfied. The compressor can rotate up to 80, 000rpm at maximum then the coil supply temperature of supercritical helium is 3.5K.
The world largest supercritical helium pump is developed by Japan Atomic Energy Research Institute (JAERI) in collaboration with Kawasaki Heavy Industries, Ltd. (KHI) in order to supply supercritical helium for the Demonstration Poloidal Coil (DPC) which are forced-flow cooled type superconducting pulse coils. The helium pump is one of key components of the DPC test facility, which was completed in the middle of March 1988. This pump development is a step for a large helium pump development for the Fusion Experimental Reactor (FER) which requests supercritical helium with mass flow rate of a few thousand gram per second. Double acting bellows mechanism is adopted for this pump to realize a high pump efficiency with large mass flow rate. In the performance test, the design flow rate of 350g/s is achieved with a pump head of 1.0 bar at both working pressure of 10 bar and 6 bar. The pump efficiency, indicated by adiabatic efficiency, is measured to be 64% in the design operation points, which exceeds to the design value of 60%. Maximum flow rate of 680g/s and 640g/s are obtained with pump head of 1.0 bar at the preliminary performance test and the final performance test in the DPC test facility, respectively.
A tape conductor composed of Nb3Sn and copper is presented in order to exemplify the conductor design based on the magnetic stability criterion. The tape can carry an overall current density as high as 300Amm-2 in a magnetic field of 10T. The influence of transient thermal disturbances on the stability of the tape conductor has been analyzed theoretically. Two distinct processes characterize the recovery of a transient temperature rise. One is the cool-down of copper due to the heat transfer to the coolant and the other is controlled by the thermal diffusion in Nb3Sn. These two processes lead to two conditions to be met for stability provided that disturbances are of transient distributed nature. It is proven that these conditions are equivalent to a single criterion of the magnetic stability. The energy density of the maximum tolerable disturbance is also discussed.
It is important for rotors of superconducting generators to maintain a stable flow pattern of liquid helium to prevent an accidental transition of superconducting field windings into the normal state. Liquid helium within the rotating helium pool of superconducting generators has two major flow patterns. One is a gravity dominant flow pattern and the other is a centrifugal force dominant flow pattern. The former has a flat horizontal surface of a liquid, and the latter has a cylindrical one. This paper describes the transition phenomena between these two flow patterns. The results of a visual experiment using water, fron 113 and silicon oil were presented in the first report of this paper. The second report at first describes experimental data of liquid helium obtained using a rotating helium pool, and then compares these experimental data with the results of a visual experiment.