The major activities of SMES research in the organization of Japanese government (New Energy Development Organization, NEDO) and of private sectors (Engineering Advancement Association, ENAA) have been reported. In this activities, the 5GWh SMES which will be usefull for peak shaving of the utility network has been conceptually designed and the economic prospect has been discussed. The superconducting coil with a diameter of 400m will be constructed underground in a depth of 150m. The Nb3Sn cables carrying 700KA currrent will be laid in a package of conductor assembly which includes the structure for axis-oriented electromagnetic forces. The rock bears the radial electromagnetic forces of the coil through thermally insulated plastic composite. The wall of liquid helium vessel is mechanically supported by hook pins to the coil assembly. The vaccum wall is fixed to the rock by bolts compatible with rock stabilization. All of these coil assembling will be performed during 4 years term. The term of total construction including pre-construction works has been estimated to be 8 to 9 years. Finally the direct construction cost can be estimated by taking into account the weight of each materials, material unit cost and labour cost. The estimation of the total construction capital for 5GWh SMES has been performed including the indirect capital and contingency. Thus the economic discusion has been performed comparing the construction capital with the economic break even cost. At last they came to the conclusion that the construction of 5GWh SMES is feasible in a technical view point and the unit can meet an economical requirement of into utilities at the year 2000.
The energy counting rate of acoustic emission (AE) has been measured as a function of energizing current for several dry wound superconducting solenoid in order to pursue the frictional motion of the conductor during the energization. A simple theory based on the frictional motion predicts that the AE rate increases monotonically with increasing current. This has been confirmed by the experiment for some test coils. Some practical magnets, however, exhibit different behaviors, depending on the type of winding: layer winding and pancake winding. For the layer wound coils, the AE rate has a peak in the high current region when the current is increased. For the pancake wound coils, the AE rate has a peak in the low current region. These behaviors are also discussed on the basis of the conductor motion.
So as to increase both of the shielding effect for protecting the superconducting field winding against asynchronously rotated armature-reactive magnetic fields and the damping effect for rotor swings in transients, the double electromagnetic shielding scheme has been lately established in superconducting alternators. One of elctromagnetic features, which stem from the adoption of a shielding system with relatively large time constant and the superconducting field circuit with exceptionally large time constant, is that an excitation voltage ceiling should be enormously raised in the case of typical field forcing control to provide supplementary damping force of the rotor, to ensure a good dynamic voltage regulation, and then to guarantee a power system stability. Nevertheless, in such a superconducting system, a high value of field current variation could ont be acceptable from points of the limitation of a critical magnetic field changing rate, a temperature rise caused by ac losses in superconductors and other cryogenic rotor components, and so on. Even though a great deal of field forcing might be acceptable, only very little improvement could be achieved in the dynamic performance. Hence it might be of necessity that new alternative contol schemes have been proposed, for instance, a shield winding control and a static reactive power compensator control connected at the terminal of the generator, instead of the conventional field forcing control. The paper has reviewed such new control schemes besides the conventional typical control, and discussed their control performances based on computer simulations which the author has done up to now.
A new parameter which is obtainable with a breaf calculation is introduced for simplification of the design procedure of current leads for superconducting magnets. The parameter enables us to draw a useful design chart without explicit consideration of such quantities as conductor length, cross-sectional area, heat transfer coefficient and cooling perimeter. This chart gives to a wide variety of current leads the detailed information on the optimum design-viz. geometric dimension, heat flow into liquid helium and pressure drop of coolant. An adiabatic approximation derives a simple expression for reliability of current leads in the case of an accidental decrease or stop of the coolant flow. Change in the cross-sectional area along the conductor is shown to improve the current lead performance to some extent.
A liquid helium temperature fatigue testing system was developed at the National Research Institute for Metals, Tsukuba Laboratories. The system is equipped with a recondenser installed in the test machine cryostat. Helium mist is transferred to the recondenser from the refrigerator, and the evaporated helium gas in the cryostat is recondensed into liquid helium. Thus, the liquid helium level in the cryostat is kept constant without the addition of liquid helium during testing. Continuous operation of about 1000 hours has been achieved with this fatigue testing system.
Acoustic emission (AE) from small superconducting coils has been analysed aiming at the application to the monitoring system of large-scaled magnet. It was clarified that AE monitoring was useful for investigation of mechanical disturbances in the magnet. The origins of AE during magnet operation were investigated, and confirmed that it was originated from mechanical disturbances such as wire motion and/or epoxy cracking. The AE during cooling down or that after the quench has also been analysed to detect the instabilities. The results suggest that the AE from the magnet accompanied with temperature change reveals the degradatios of the magnet performance.
In order to obtain the fundamental data for the application of the forced cooling method to a pulsed magnet, the thermal and hydrodynamic behavior of the supercritical helium in the forced flow cooling superconductor was experimentally investigated with the hollow superconductor (L=6.5m) and the stainless steel tubing (L=3.0m). (1) In case of giving a stepwise heat input to the entire conductor, the transitional stage was observed after heating, which was accompaning the decrease and oscillation of the mass flow rate in the conductor, and as a result, it was found that cooling power of supercritical helium decreased and that the temperature distribution along the conductor had the maximum at the middle of the conductor. (2) In case of repeating pulse heat input, the thermal characteristics of supercritical helium and conductor was influenced by the period of heating. Especially, when the period of heating became short, cooling power of supercritical helium decreased after heating because the thermal characteristics of supercritical helium under pulse heating resembled that under continuous heating.
Thermal and mechanical properties of advanced composite materials have been studied in order to examine their applicability to cryogenic use. Carbon, silicon carbide and alumina fiber unidirectionally reinforced epoxies were prepared as advanced composite materials and their cryogenic properties were compared with that of glass fiber reinforced epoxy. Thermal conductivity and thermal contraction have been measured in both directions parallel and perpendicular to fibers in the temperature range down to liquid helium and liquid nitrogen temperature, respectively. In order to investigate mechanical properties, four point flexural test was also performed at room, liquid nitrogen and liquid helium temperature and Young's modules and breaking stress were calculated. Considering the specific modules and the ratio of breaking stress to thermal conductivity, the advanced composite materials are found to be suitable for cryogenic structural support members.