The time evolutions and three-dimensional temperature profiles in a cryocooled superconducting bulk disk have been investigated using a finite element method (FEM) after applying pulse field magnetization (PFM). The bulk is either cooled down along the ab-plane through the brass support component and magnetized using a split-type coil, or cooled along the c-axis and magnetized using a solenoid coil. The temperature rise ΔT due to the magnetic flux intrusion in the case of the “ab-plane cooled type” is experimentally small and the trapped field BTP is enhanced as compared to the “c-axis cooled type”. The calculated temperatures T'(t) can effectively reproduce the measured T(t) with an appropriate assumption of the heating area and total generated heat Q. The heating area is wider and the Q value is relatively smaller in the “ab-plane cooled type” as compared to the “c-axis cooled type”. These analytical results suggest that, in the “ab-plane cooled type”, cooling along the high thermal-conductive direction in the bulk magnet and the increase in total heat capacity due to close contact of the bulk magnet and the brass support component are effective for reducing ΔT and enhancing BTP.
We recently proposed a new design for a high-temperature superconducting thin-film fault-current limiter (FCL), which uses high-resistivity Au-Ag alloy shunt layers instead of the pure gold (or silver) shunt layers conventionally used. Due to the much larger resistance of the Au-Ag alloy layers, the FCL elements withstood very high electric fields (> 40 Vpeak/cm), and realized a very high switching power density, ∼2.0 kVA/cm2. The composition of our FCL element is very simple, and the achieved power density is more than five times higher than conventional devices, which leads to a dramatic reduction in the amount of expensive superconducting thin films required. Similarly, Kinder et al. recently proposed a new coated-conductor-based FCL element, which achieved a relatively high electric field of 2.7 Vpeak/cm. We estimated the cost of our thin-film FCL elements used in a typical 6.6 kV FCL that is introduced in a distributed power supply site. We also estimated the cost of coated conductors used to produce the FCL, and compared the two.
We studied the use of bamboo as a material of low environmental impact. Bamboo is widely distributed in warm climates, naturally decomposes and is characterized by the properties of excellent elasticity and ability to absorb water. We believe that a bamboo-ice composite system can be used as a substitute for glass fiber reinforced plastics (GFRP), which do not naturally decompose, in electrical insulation systems that operate at cryogenic temperature. In this paper, we report the effect of field direction on alternating-current (ac) breakdown properties of the bamboo-ice composite system in liquid nitrogen. The ac breakdown properties of the bamboo-ice composite system show strong anisotropism.