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Hot-spot temperature limits for YBCO epoxy-impregnated coil to be safe from damages caused by quenches are experimentally investigated using small-scale test coils. In the authors’ previous study, it is found that the hot-spot temperature limits for YBCO paraffin-impregnated coils are around 500 K where the critical current of YBCO wire is degraded thermally. However, in the cases of the epoxy-impregnated coils, it is shown that the hot-spot temperature limits are around 300 K, much lower than those of the paraffin-impregnated coils. In this paper, a reason for those lower hot-spot temperature limits of the epoxy-impregnated coils is discussed.

In this work, heat transfer characteristics of HTS wire in a conduction-cooled epoxy-impregnated HTS coil are studied by making winding pack stacking pieces of Bi/Ag sheathed wires insulted by Kapton tapes. To check the validity of the measured data, hot-spot temperature is calculated for an epoxy-impregnated experimental coil wound of Bi/Ag sheathed wire by a thermal equilibrium equation using the measured data, and quench damages of the coil are estimated. The estimated results are compared with quench-test results of a Bi/Ag sheathed wire coil, and it is shown that the both results reasonably agree with each other.

A quench detection method of a high-temperature superconducting (HTS) coil using a cowinding method is studied. It is experimentally shown using a small YBCO test coil that the cowinding method is highly effective in canceling the inductive voltage component and can detect a quench occurring in an HTS coil with high sensitivity, compared with a commonly used bridge-balance method. An HTS coil is damaged by a quench when hot-spot temperature exceeds a certain threshold. The authors also experimentally investigated conditions to keep the hot-spot temperature of coils wound of YBCO tapes below a safe level, using the highly sensitive cowinding quench detection method.

HTS wires in coils are subjected to hoop stresses due to electro magnetic forces and thermal contractions. Influence of repeated and non-repeated hoop stresses is investigated by making an experimental apparatus to apply hoop stresses mechanically to dry (non impregnated) and epoxy-impregnated HTS test coils. In the experiment it was found that a critical current of a dry coil was more degraded by the hoop stresses than that of an epoxy-impregnated coil. In the paper, distribution of hoop stresses to layers in HTS coils are investigated and based on the experimental results, differences of critical current degradations of dry and impregnated coils are studied.

In order to stop the global warmth due to the CO2 concentration, the energy use should be decreased. The investment of building construction industry in Japan is about 20% of GDP. This fraction is much higher than in most developed countries. That results the Japanese building construction industry including residential use consumes about one third of all energy and resources of the entire industrial sectors. In order to save energy as well as resource, the recycle of the building materials should be urgent to be carried out. In this paper, we focus on the potential energy savings with a simple calculated method when the building materials or products are manufactured from recycled materials. We examined three kinds of residential buildings with different construction techniques and estimated the decreased amount of energy consumption and resources resulting from use of recycled materials. The results have shown for most building materials, the energy consumption needed to remake housing materials from recycled materials is lower than that to make new housing materials. The energy consumption of building materials in all case-study housing can be saved by at least 10%. At the same time, the resource, measured by mass of building materials (kg) can be decreased by over 50%.

Sure quench protection of HTS coils is essential for their sustainable operations in their real applications to HTS power devices. The authors investigate conditions to safely protect HTS coils from quench damages by a detect-and-dump-type active method. In the previous work, the safe area in the V qs versus τ plane was identified by experiment using test coils wound of Bi/Ag-sheathed wires, where V qs is the quench detection voltage, and τ is the decay time constant of the coil current in the active protection method. In this work, the safe area is obtained by numerical calculation, making a simulation model of a winding pack of a coil wound of Bi/Ag-sheathed wires. The analytical results well agree with those of the experimental results, and it is shown analytically that condition to safely protect a coils wound of Bi/Ag-sheathed wires from a quench damage can be analytically predicted.