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A conduction-cooled high temperature superconducting (HTS) magnet for the SPMS was fabricated and tested. To achieve an adequate uniformity of background magnetic field, a split-pair winding configuration is used. Room temperature bore of this magnet was 38 mm (length) × 134 mm (width) × 360 mm (depth) in dimension. The magnetic field uniformity of HTS magnet was achieved lower than 1% within the virtual sample region 15 mm (width) × 100 mm (depth). Also, this HTS magnet could be operated to generate 3 T for 7 h.

The authors designed and manufactured a toroidal-type superconducting magnetic energy storage (SMES) system. The toroidal-type SMES was designed using a 3D CAD program. The toroidal-type magnet consists of 30 double pancake coils (DPCs). The single pancake coils (SPCs), which constitute the double pancake coils, are arranged at an angle of 6° from each other, based on the central axis of the toroidal-type magnet. The cooling method used for the toroidal-type SMES is the conduction cooling type. When the cooling method for the toroidal-type SMES was designed, the two-stage Gifford–McMahon (GM) refrigerator was considered. The Bi-2223 HTS wire, which was made by soldering brass on both sides of the superconductor, is used for the magnet winding. Finally, the authors connected the toroidal-type SMES to a real-time digital simulator (RSCAD/RTDS) to simulate voltage sag compensation in a power utility.

This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of 22 of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.

A 600 kJ HTS SMES is developed and tested in Korea. The HTS SMES consists of 22 double pancake coils wound on each aluminum alloy bobbin. It is cooled by two GM cryocoolers down to around 6 K and current is charged through HTS current leads up to 275 A. Beside the heat penetration from room temperature structures, heat generation in the HTS coil is inevitable because of the joint resistances and the intrinsic property of the HTS tape such as index loss. Moreover, during the charging and discharging operation, AC loss of the HTS conductor and eddy current loss in the coil bobbin and metallic structures are generated. Therefore, the heat generation should be effectively removed by the cryocooler to ensure the stable operation of the coil. In the HTS SMES, aluminum alloy conduction plates outside the each coil are used as thermal paths to the cryocoolers. This paper describes the thermal characteristics of the HTS SMES for the charging and discharge operation.

In order to measure the superconducting transition temperature, the critical current and the alternating current (ac) loss on short samples of high temperature superconducting (HTS) tape, a conduction cooled cryostat has been designed and built. Two closed-cycle coolers provide cooling with an ultimate sample temperature below 20 K. The main temperature sensors are located on the sample mount (B1), on the CVI cold head (B2), and on the Dakin cold head (B3). Temperature regulation is provided by 50 W of electrical heater that opposes the cooling power from the cold heads. Temperature control feedback is by means of temperature sensors co-located with the heaters on the second stage of the cryocoolers. AC losses on the HTS tape sample were measured at 30 K so that the developed device performance was evaluated. In this paper, the design, fabrication and test results on the conduction cooled cryostat are presented.

The operation of the SMES system can be divided into three modes such as charging, operating and discharging. During the charging and the discharging modes, a magnetic field variation due to the current increase and decrease generate eddy current losses in the SMES system. The eddy current loss in discharging mode is the major factor to be considered because the operating time in the mode is fixed, whereas the charging mode has the arbitrary operating time which is not fixed. In this paper, we present the analysis results of the eddy current losses which are generated in the 600 kJ class HTS SMES system during the discharging mode.

Superconductor is developed for applications in high-power devices such as power-transmission cables, transformers, motors and generators. In such applications, HTS tapes are subjected to various kinds of stress or strain. AC loss is also important consideration for many large-scale superconducting devices. In the fabrication of the devices, the critical current ( I c ) of the high temperature superconductor degrades due to many reasons including the tension applied by bending and thermal contraction. These mechanical loads reduce the I c of superconducting wire and the I c degradation affects the AC loss of the wire. The I c degradation and AC loss of Bi-2223 HTS tape were measured under tension and bending conditions at 77 K and self-field. Moreover, the frequency characteristics of AC loss was measured at the 30–480 Hz. As a result, self-field penetrates the deeper into the conductor at the lower frequency, which means higher self-field losses per cycle.

HTS power transmission cables appear to be the replacement and retrofitting of underground cables in urban areas and HTS power transmission cable offers a number of technical and economic merits compared to the normal conductor cable system. A 30 m long, single-phase 22.9 kV class HTS power transmission cable system has been developed by Korea Electrotechnology Research Institute (KERI), LS Cable Ltd., and Korea Institute of Machinery and Materials (KIMM), which is one of the 21st century frontier project in Korea since 2001. The HTS power cable has been developed, cooled down and tested to obtain realistic thermal and electrical data on HTS power cable system. The evaluation results clarified such good performance of HTS cable that DC critical current of the HTS cable was 3.6 kA and AC loss was 0.98 W/m at 1260 Arms and shield current was 1000 Arms. These results proved the basic properties for 22.9 kV HTS power cable. As a next step, we have been developing a 30 m, three-phase 22.9 kV, 50 MV A HTS power cable system and long term evaluation is in progress now.

Research and development on superconducting magnetic energy storage (SMES) system have been carried out to realize efficient electric power management for several decades. Korea Electrotechnology Research Institute (KERI) has developed a 3 MJ/750 kVA SMES system to improve power quality in sensitive electric loads. It consists of an IGBT based power converter, NbTi mixed matrix Rutherford cable superconducting magnet and a cryostat with HTS current leads. A computer code was developed to find the parameters of the SMES magnet which used minimum amount of superconductors for the same energy storage capability, and the 3 MJ SMES magnet was designed based upon that. This paper describes the fabrication and experimental results of the 3 MJ/750 kVA SMES system.

A high temperature superconductor (HTS) power transmission cable is usually made of several layers of helically wound superconductor tapes. The current distribution among the conductor tapes is controlled mainly by pitches and winding directions of the layers, because the inductance of the layer is determined by the pitch and the winding direction. Two winding directions––right and left––are possible for each layer, and we can list up many possible combinations of winding directions. If we choose a good combination we can find the optimal pitches and make an even current distribution. However, with a bad combination of the winding direction, it is almost impossible to find a solution. We developed a software code to calculate the currents of the layers. With this software we studied the effect of the winding direction on a four-layer cable by a statistical way. A brief description of the software, calculation results and discussions will be presented.

The fabrication and the test results of the superconducting magnet for a whole body MRI are presented. The magnet consists of a main coil with six solenoids, a shielding coil with two solenoids, and six sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore to compensate the inhomogeneous field components that originated in insufficient tolerances, installation misalignments, and external ferromagnetic materials near the magnet. In addition, the magnet is enclosed by a horizontal type cryostat with the room temperature bore of 80 cm. According to the test of the MRI magnet, the central field of the magnet is 1.5 T with a field homogeneity of 9.3 ppm on 40 cm DSV (the diameter of spherical volume). Some magnetic resonance images for human body have been achieved by employing this magnet.

The studies on the conduction-cooled superconducting magnets are actively underway with rapid advancement in refrigeration technology recently. YBCO coated conductor (CC) is one of the promising conductors for a conduction-cooled superconducting magnet because of increasing the operation temperature of magnets and being able to have cost collectiveness with conventional copper conductor in the future. However, it is known that quench propagation velocity in high-temperature superconductor (HTS) is two or three orders of magnitude slower than that in low-temperature superconductor because of its large heat capacity and the high operating temperature. The hot spot will emerge in local region if a critical current is non-uniform along the length of HTS tape and eventually, it causes permanent destroy for the whole HTS tape. Based on the protection of YBCO CC, it is necessary to determine a suitable stabilizer thickness for YBCO CC so that the temperature of hot spot in local area does not exceed the permissible temperature. In this study, we have established a suitable thermal analysis model, and analyzed minimum quench energy and thermal properties for three kinds of YBCO CC samples with different stabilizer thickness, which are fabricated by Superpower Incorporated, using finite element method.