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We developed a prototype of a high-Tc superconducting (HTS) linear synchronous motor (LSM) and evaluated its operational performances to obtain the preliminary design data for a test vehicle having a speed of 518.4 km/h. The HTS electromagnet was fabricated using a non-insulated (NI) GdBCO HTS coil, which was designed to produce a magnetomotive force of 300 kA-turns at a cooling temperature of 20 K. A two-stage Gifford-McMahon cryocooler was used to cool the electromagnet. The prototype was tested up to 2.7 kN sufficient to the required thrust of the test vehicle. The thrust characteristics shown by changing the operating conditions were also consistent with the simulation results. The HTS electromagnet was successfully operated during the test, and there was no fault in the NI HTS coils. Finally, we confirmed the design feasibility of HTS LSM for a test vehicle.

The super high field magnets using superconducting wires have been promisingly applied for thermonuclear fusion power generation such as Korea Superconducting Tokamak Advanced Research (KSTAR) and International Thermonuclear experimental reactor (ITER) systems. The quench detection system (QDS) is essential for high reliability in the super high field magnet facilities. Generally, the quench voltage detection system, which uses resistive voltages, has been adopted. Such an ITER magnet, the maximum operation current and voltage of superconducting keeps over 60kA and 50 kV DC. Generally, in the case of medium power, the power transformer has been adopted for QDS as an isolated power due to stable insulating and durable characteristics. However, unfortunately, the magnetic saturation of electric steel for power transformer remained fragile as well as the volume is increased under super high field magnet. From this reason, authors suggest the electron quench detection device (EQDD) module. The main functions of EQDD are to convert high voltage signals of magnet into voltage-drop, and then send into quench monitoring system through optic cable. The EQDD module needs to isolate power system since EQDD module should be operated under high voltage insulation. From this reason, authors apply the wireless power system for EQDD module as a reasonable option instead of power transformer since the wireless power system can transfer power through any non-metallic media between resonance antenna (Tx) and receiver (Rx) coils. In this study, authors describe the possibility of conceptual design for quench detection system with high insulation under super high field magnet using wireless power transfer technology. As the EQDD including isolated wireless power should be electrically shielded, the shielding effects for Tx coil is investigated under different intervals of shielding barrier. Additionally, to expand the delivery distance between Tx and Rx coils, the operation and thermal characteristics for transfer efficiency are investigated under 370 kHz and 750 kHz RF generators, respectively.

Our research team has developed a wireless power charging system for a high-speed superconducting magnetic levitation train based on the strong resonance coupling method to improve the transfer efficiency and stability. Especially, the range of resonance frequency is one of main key design parameters to fabricate the system since the high resonance frequency can improve the transfer distance easily. On the other hand, since the sensitivity of impedance matching between antenna and receiver coils is increased in the range of higher frequency, the technique of stable impedance matching design including elaborated rectifying subcircuit has been required to commercialize under high-power transfer applications. For this reason, the various transfer characteristics under different ranges for resonance frequency conditions should be evaluated to accomplish improve the transfer efficiency. Thus, in this paper, the transfer efficiency of the moving position of receiver (Rx) coil and consumption of liquid nitrogen were measured at 100 and 370 kHz with 250 W, respectively. In addition, the operating characteristics of the cooled copper Rx and HTS Rx coil were evaluated under 100 and 370 kHz with 250 W, respectively.

The wireless power transfer (WPT) using magnetic resonance coupling method has been known to have the advantage of being able to transfer power across large air gap with considerably high efficiency. As well as, as such a method can eliminate the physical contact loss in the system, it provides an ideal solution for the problem of contact losses in the power applications. Especially, since it is difficult to reduce the energy loss at connectors in the high temperature superconducting (HTS) magnet system, the WPT technology has been promisingly expected as a noble option to transfer electric power without physical contact from room temperature to very low temperature cooling vessel. From this point of view, authors proposed the combination WPT technology with HTS coils, it is called as, superconducting wireless power transfer (SUWPT) system. The SUWPT technique can be expected to solve the problem of the contact loss in the HTS joints, as well as, use with high levels of and low study, safety maintenance. In this authors examined transfer profiles between copper enameled antenna and HTS receiver coil with the usable frequency range at 13.56 MHz of RF power amplifier as long as the receiver is within 1.5 m distance under Styrofoam and stainless cooling vessels, respectively.

Since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power during movement. Above all, the WPT technology in the MAGLEV can reduce the cost of tunnel construction since the space of conventional power line doesn’t required. From these merits, the WPT systems have been started to be applied to the wireless charging for various power applications such as transportations (train, underwater ship, electric vehicle). In this study, as a practical approach, authors investigate transfer efficiency and cooling cost for multi-Tx and multi-sized single Tx coils under different size of Rx coils arrays, respectively. Additionally, authors investigated transfer ratio at HTS Rx with helix and spiral Tx coils under different interval. As well as, authors evaluate cooling cost of different sizes of HTS receiver under long single and multi-copper antenna arrays based on nitrogen evaporation method.

A flux pump is one possible way to reduce the heat load of a superconducting magnet system by replacing mechanical connections with magnetic coupling. However, the heat loss of the flux pump should be analyzed so that it can be applied to conduction-cooled magnets because of the low temperature margin in conduction-cooled systems. In this paper, the simplified thermodynamic behavior of a linear-type flux pump system is investigated. The system is assumed to be cooled by a conduction cooling system. The heat generation of a linear-type flux pump is calculated based on the ac loss theory. The temperature stability of a thermal link for the flux pump system is analyzed with different design parameters. A design method is suggested for the thermal conductivity of the thermal link in a flux pump of conduction-cooled magnet by summarizing the results of the analysis.

The rotary flux-pump using HTS tape has been studied for superconducting rotating machinery application. The charging speed and saturation current of the rotary HTS flux-pump is closely related to magnetic flux linkage passing through the HTS tape. To analyze charging parameters that effect pumping rate and saturation current of the flux-pump, methods of changing the rotating speed, shape of permanent magnet, width of HTS tape, and magnetic flux intensity have been investigated in previous studies [1] – [3] . In this paper, we have tried to test three cases to investigate the pumping rate and saturation current: 1) two different background materials, iron and Bakelite, were used to compare the magnetic flux linkage reinforcement; 2) two HTS tapes were overlapped to extend the magnetic flux linkage area, and each HTS tape was connected to an HTS coil; and 3) the parallel joint was conducted between the flux-pump and the HTS coil to compose a closed loop for persistent current mode. In order to measure the charging speed and pumping rate, a Hall sensor was installed at the center of the HTS coil.

High-temperature superconductors (HTSs) have a much larger thermal margin than low-temperature superconductors, owing to their high critical temperatures. This characteristic allows HTS magnets to tolerate extremely high heat loads that may arise from radiation. Therefore, research on the development of HTS quadrupole magnets is progressing widely. Quadrupole magnets are commonly used for focusing the transported beams of particles in accelerators. In order to focus the beam, the quadrupole magnet uses an iron yoke with a hyperbolic contour. However, the iron yoke induces nonlinear magnetic characteristics because of saturation. Therefore, an air-core HTS quadrupole magnet is proposed to improve the magnetic characteristics. In this paper, we design air-core and iron-core HTS quadrupole magnet models using a harmonic matching method. The field gradient and effective length of both magnets are 12.1 T/m and 550 mm, respectively. In order to verify the performances of the proposed air-core quadrupole magnet, the magnetic field gradient, field uniformity, and effective length are analyzed for operating currents ranging from 50 to 400 A.

Our research team has been developing a wireless power charging (WPC) system for electric vehicle (EV) using superconducting and normal conducting resonance coils in order to improve the transfer efficiency and stability. In the practical approach, the EV, which is installed outside, is wirelessly charged without moving. The antenna (Tx) coil is disclosed by rain or snow and so on. From this reason, the transfer characteristics surrounded by water circumstance, i.e., fresh water or salt water, should be evaluated to commercialize In addition, the high-voltage WPC system generates strong electromagnetic fields (EMFs) around Tx and receiver (Rx) coils. As the human safety with respect to EMFs is an important measure, it is required to identify the condition under which human exposure complies with the safety regulations. Thus, in this paper, as a fundamental approach, the spatial spots of current around Tx and Rx coils were measured. As well as, the transfer efficiencies of a WPC unit under different water circumstances of Tx and Rx coil were measured with an RF generator of power of 150 W, 370 kHz.

Recently super high-speed magnetic levitation (MAGLEV) using high-temperature superconducting (HTS) magnet has been expected as next-generation transportation since superconducting magnet can keep mighty levitation force. The superconducting magnet at MAGLEV train should be continually charged with high power in order to keep stronger and stable levitation force. Practically, since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance-coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications, such as transportations (train, underwater ship, electric vehicle). However, it has obstacles to commercialize, such as delivery distance and efficiency. To solve the problems, authors proposed the technical fusion using HTS resonance coil in the WPT system since the superconducting wire has merits a larger current density and higher Q -value than normal conducting wire. In this study, authors described the conceptual design of HTS receiver (Rx) coil with multi-copper antenna (Tx) coils. The priority characteristics of moving HTS receivers under multi-copper Tx coils are compared with and various copper Rx coils with radio frequency power of 370 kHz below 300 W.

The superconducting wires have been developed for high field magnet, transformers, motors and so on. The quench detection and protection system are essential for safety operations of the HTS facilities. The high voltage signal conditioner (HVSC) method is generally used for the quench detection and protection, however especially for high voltage operation magnet such as international thermonuclear experimental reactor (ITER) magnet (56 kV, DC), it is difficult to apply to HVSC method due to the risks in terms of high voltage sparks. As well as, the power supply for HVSC should be isolated since the ITER magnets, which is supplied by 15 MA, generate about 10 T (tesla) strong magnet. To solve these problems, insulation resistance of power supply should be larger than 500 MΩ; a lower resistance can affect the common-mode voltage of the differential amplifier in the HVSC system. From these reasons, the wireless power transmitter (WPT) system has been considered as one of reasonable options to solve insulation resistance obstacles since WPT system can transfer power through any non-metallic media between antenna (Tx) and receiver (Rx) coils. In this study, authors described the conceptual design and fundamental performances of quench detection system for high field magnet based on resonance coupling method with RF power of 370 kHz 200 W.

Our research team has been developed wireless power charging (WPC) system for electric vehicle using superconducting resonance coils in order to improve the transfer efficiency and stability. The strong eletromagnetic fields (EMFs) are generated around antenna (Tx) coil and receiver (Rx) coil in the high power applications of wireless power transfer (WPT) technology. As the Human Safety with respect to EMFs is an important measure, it is required to identify the condition under which human exposure complies with the safety regulations. Since the WPC system based on the resonance coupling method provides basic restrictions for EMFs in terms of internal electric field and specific absorption rate (SAR) to prevent effects on nervous system functions and excessive localized tissue heating, the effect of EMFs should be investigated. Especially., as the strong EMFs of high power applications such as electric vehicle (EV) and train charging system can affect the human body., various researches have been required in order to commercialize. In this paper., as a fundamental approach, authors indirectly investigated the influence of EMFs for food elements using fruits and vegetable since it is practically difficult to make clinical trial for human body. Thus, in this study, authors presented thermal distributions by EMFs between Tx and Rx coils under different frequency of 370 kHz and 750 kHz, respectively. As well as authors investigated rates of browning reactions in vegetable (potato) and fruits (banana, apple, pear), which are evaluated under exposure and non-exposure of EMFs with 370 kHz RF generator of 200 W.

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electrical vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. However, there are challenges in its commercialization, such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using high-temperature superconducting (HTS) resonance coil in the WPT system, which is called superconducting wireless power transfer for electric vehicle (SUWPT4EV) system. Since the superconducting wire has merits, i.e., a larger current density and a higher Q value than normal conducting wire, the HTS antenna coil enables to deliver a mass amount of electric energy in spite of a small-scale antenna, as well as is possible to keep much stronger magnetic fields out in the peripheral regions. Thus, the SUWPT4EV system has been expected as a reasonable option to improve the transfer efficiency of large electric power. In this study, as an advanced approach, we proposed the advanced SUWPT4EV system with inserted resonator using noncooled copper, cooled copper, and HTS resonators, respectively, in order to expand the transfer distance and improve the transfer ratio. In this paper, we presented operating characteristics of the advanced SUWPT4EV system and achieved the improvement and effects of transmission power for inserted resonators within 40-cm distance under radio frequency power of 370 kHz below 600 W.

In this paper, characteristics of a thermally and magnetically triggered switch for a high-Tc superconducting (HTS) power converting system are experimentally analyzed. For verifying the efficiency of the suggested switch, current charging and discharging tests using heater-triggered switch with or without an external magnetic field are performed. Charging tests are performed with two charging sequences, i.e., CS1 and CS2. Each sequence is experimented with two kinds of heater currents to maintain different temperatures. Saturation current and saturation time are detected to calculate the pumping rate. Two discharging sequences, i.e., DS1 and DS2, are used for discharging tests with heater current to maintain 120 K. From the results, normalized load energies are calculated and compared.

This paper deals with the effect of magnetic flux diverters on the current decay behaviors of high-temperature superconducting (HTS) coils which operate in semipersistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machines, the HTS field coil can be designed to operate in PCM to obtain a steady magnetic field during operation. Due to the alternating magnetic field from the armature winding, the HTS field winding experiences an external magnetic field. As a result, the additional magnetization ac loss in the field coil would be induced, and it affects the current decay characteristics. In order to improve the current decay behavior of the HTS field coil, the use of flux diverter made of magnetic material can be considered. In this paper, we experimentally investigated the current decay characteristics of HTS field coils with magnetic flux diverters under alternating magnetic field. The measurement setup, which is composed of HTS field coil and armature coil, was fabricated. The measurement test of the current decay on the HTS field coil in PCM operation was carried out as functions of the amplitude and frequency of the armature coil.

This paper deals with the analysis of the electromagnetic and mechanical properties of a high-temperature superconducting (HTS) coil, as well as its characteristic as determined through tests using strain gauges. When an operating current is applied to an HTS coil, strain is generated by electromagnetic force. However, additional strain effects in the HTS coil are formed by the Joule heating during quench. Strain was measured with a full-bridge strain gauge mounted directly over the turns. We fabricated an HTS coil wound in a single pancake type to investigate strain characteristics. We also investigated structural analysis by a finite-element method to calculate the strain of the HTS coil. In tests, the strain in the HTS coil was measured during excitation. Test results of the HTS coil have been compared with the theoretical results. Finally, we performed quench propagation tests and could verify the strain effect during quench. The reaction times of the strain gauge at 30 and 80 A are 31.8 and 4.3 s, respectively.

This paper presents experimental results of the designed high-Tc superconducting (HTS) power converting system with multiple GdBCO magnets. The system is tested by various sequential controls of four heater-triggered switches and an electromagnet, which consists of two energy storage magnets (ESMs). The experiments are mainly composed of two modes. The first one is a simultaneously operating mode (Mode1), and another is an alternative operating mode (Mode2). Each two sequences are performed at Mode1 (CS1 and CS2) and Mode2 (CS3 and CS4) for charging the ESMs, respectively. In those experiments, the average pumping rate of each sequence is calculated at about 17.55, 41.26, 10.25, and 25.83 mA/s, respectively. In the discharging test, two sequences are tested. Load energy is calculated from load voltage and current due to the difference between precharged energy to verify which operating mode is more effective. Load energy of each sequence reached about 47.97 and 38.83 J after 2000 s, respectively.

The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various HTS wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n value intrinsically, they are required to be charged from external power system through leads or internal power system. The portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for superconducting HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system.

As the wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications such as transportations (train, underwater ship, electric vehicle). Especially, in the case of high speed magnetic levitation (MAGLEV) train, The MAGLEV systems inherently have advantages in higher efficiency due to smaller air gap for wireless power transfer system between guidance and train. Even though it makes possible a convenient power charging system based on strong resonance coupling method, the transfer efficiency is limited structurally. This study aims for the design of inserted resonance coil (Sx) between antenna (Tx) and receiver (Rx) coils with high efficiency and stability in wireless power charging system for high speed MAGLEV train. In this study, authors described design methodology of inserted resonance coils to improve the efficiency for form of different sizes of Sx coil with radio frequency (RF) power of 370 kHz 400 W.

As the wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications such as transportations (train, underwater ship, electric vehicle). This study aims for the design and analysis of antenna and receiver with high efficiency and stability in wireless power charging system for superconducting magnetic levitation (MAGLEV) train. Authors have already been developed superconducting wireless power charging (WPC) system for MAGLEV train using resonance copper antenna (Tx) coil HTS receiver (Rx) coil. Since the Tx and Rx coils can be placed on guidance and superconducting magnet at train, respectively, the installation cost of Tx can be considerably reduced. In this study, authors described and compared the practical design of permanent magnet between copper Tx and HTS Rx coils to improve the transfer efficiency through rectifying module since the permanent magnets can play a role to shift the transferred AC magnetic field. Authors measured rectifying currents under inserted permanent magnets with radio frequency (RF) power of 370 kHz below 150 W.

This paper presents the analysis of a high-Tc superconducting (HTS) power converting system, as well as its operational characteristics. The converting system can be used to charge and discharge a magnet made of series-connected pancake coils. The HTS converting system consists of two heaters, a primary copper winding, a secondary HTS winding, a series-connected HTS pancake coil, an iron core and a conventional copper load. In the experiments, the charging and discharging periods were 7.5 and 2 s, respectively. A partial region of the superconducting tape in a secondary HTS winding is switched to a normal region by a buried heating coil. To measure the converting-current with respect to the magnet flux changes, a hall sensor was installed at the center of the pancake coil. In this experiment, the charging-current and discharging-energy reached about 51.7 A and 36.8 J, respectively. The experimental results have been compared with theoretical predictions by using the finite difference method.

This paper deals with the current decay characteristics of a high-T c superconducting (HTS) coil operated in persistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machine applications, such as linear synchronous motor (LSM), the superconducting coils are designed to operate in PCM to obtain steady-magnetic field with DC transport current. This superconducting coil operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the field coils are subjected to an external time-varying magnetic field, it is possible to result in a current decay for those coils in PCM operation due to electrical AC loss. In this research, a current decay measurement system, which consists of field coil and armature coil, was fabricated to verify current decay characteristics of field coil in PCM operation against external alternating magnetic field. The current decay rate for the field coil was measured by using a hall sensor as a function of amplitude and frequency of armature coil.

This paper deals with the electrical and thermal characteristics analysis of stacked coated conductors (CCs) for current lead application. A test sample is fabricated using YBCO CCs with a stainless steel laminated stabilizer and has a heater made of the Ni-Cr wire to generate external heat disturbance. In order to evaluate a thermal stability behavior, minimum quench energy, voltage, and temperature trace are measured as a function of operating current. To verify thermal behavior in stacked CCs, numerical analysis on temperature trace is carried out using the finite-element method. The numerical simulation results are compared with the experimental data to check the validity of the simulation model.

— The electrical insulation design for a superconducting system is important when developing a high voltage superconducting apparatus as a substitute for a conventional one. In this paper, the degradation characteristics of 2G high temperature superconducting (HTS) wires, with respect to electrical breakdown tests, were studied. It was found that the superconducting materials in 2G HTS wires can be damaged in electrical breakdown and the damaged structure of 2G HTS wires results in the degradation of the Ic and index number. As a result, it was found that the degradation characteristics of the 2G HTS wires were affected by the stabilizer material and applied breakdown voltage. Thus, the hardness and electrical conductivity of a stabilizer material can be considered as design parameters in developing a high voltage superconducting coil. Finally, the cross sectional views of 2G HTS wires were presented using a scanning electron microscope (SEM).

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charg- ing without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electri- cal vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenience, safety, and fearless transmission of power. However, it has obstacles to commercialize such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using a high-temperature super- conducting (HTS) antenna in the WPT system, which is called superconducting WPT for electric vehicle (SUWPT4EV) system. Since the superconducting wire has the merits of a larger current density and higher Q value than a normal conducting wire, the HTS antenna enables to deliver a mass amount of electric energy in spite of a small-scale antenna. To apply copper-stabilizer HTS (GdBCO) coil for EV charging system practically, the transfer efficiency characteristics for the HTS wires should be investi- gated. In this study, we examined transfer characteristics with copper-stabilizer HTS antenna at 77 K and copper antenna at 77 K, respectively. The transfer distance is at 30 cm, and RF power of 370 kHz below 500 W is adopted. Moreover, in order to improve the transfer efficiency, the design considerations for the SUWPT system were described. Index Terms—Cooled copper antenna coil, electric vehicle, electromagnetic resonance coupling, high-temperature supercon- ducting (HTS) antenna coil, superconducting contactless power transfer.

The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various high temperature superconductor (HTS) wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n-value intrinsically, they are required to be charged from external power system through leads or internal power system. Thus the portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system. This feasible study deduced the design and analysis methods of the novel WPC4SM.

The contactless power transfer (CPT) technology based on strongly coupled electromagnetic resonators has been recently explored to realize the large power delivery and storage without any cable or wire across a large air gap. As the CPT technology makes possible the process of connector-free charging, it has been studied for practical applications to a variety of power applications. In the superconducting magnet system, a widespread method of electric energy supply is realized by the current lead which is one of indispensable subsystems in the power transfer equipment; however, it causes energy losses. To overcome such a problem, the combination CPT technology with HTS receiver coils has been proposed. It is called as, superconducting contactless power transfer (SUCPT) system. Such a technique has been expected a reasonable approach to provide a safe and convenient way of charging or storage without connecting joints in the superconducting applications. In this study, we presented the feasibility and various effects of transmission property from room temperature to very low temperature vessel within 40 cm under different material’s cooling vessels using radio frequency (RF) generator is 370 KHz.

As contactless power transfer (CPT) technology using strongly coupled electromagnetic resonators is a recently explored technique to realize the large power delivery and storage without any cable or wire, this technique is required for diffusion of electric vehicles (EVs) since it makes possible a convenient charging system. Typically, since the normal conducting coils are used as a transmitting coil in the CPT system, there is limited to deliver the large power promptly. From this reason, we proposed the combination CPT technology with HTS transmitting antenna, it is called as, superconducting contactless power transfer for EV (SUCPT4EV) system. As the HTS coil has an enough current density and high quality factor Q value, it can deliver a mass amount of electric energy and improved efficiency in spite of a small scale antenna. The SUCPT4EV system has been expected as a reasonable option to improve the transfer efficiency of large electric power. In this study, we examined the improvement of transmission efficiency and properties for HTS transmitted antenna coils within 40 cm distance at radio frequency (RF) generator of 60 W, 370 kHz. In addition, we achieved impedance matching conditions for different material coils between HTS and normal conductors.

Electrical breakdown voltages of liquid nitrogen (LN2) are measured by dielectric experiments, according to the gap between electrodes, and the diameter of electrodes. Also, the distribution of electric field intensity at sparkover is calculated and analyzed by the finite element method. The dielectric characteristics of LN2 depend on the amount of bubbles, as well as the duration time of the bubbles. Therefore, it is important to observe and analyze the bubble suppression characteristics of LN2 according to the conditions of the applied voltage type, electrode material, and system pressure. The bubble suppression characteristics of LN2 according to these conditions are experimented by measuring the duration time. Also, the amount of bubbles generated after the electrical breakdown is monitored by a high-speed camera system. AC and lightning impulse voltages are applied to the sphere to plane electrode system made of stainless steel, copper, and iron to compare and analyze the bubble suppression characteristics of LN2. It is found that the electrical breakdown and bubble suppression characteristics of LN2 are determined by the electrode material. Also, the bubble suppression characteristics of LN2 with the system pressure (from 0.1 MPa to 0.4 MPa) are observed and analyzed.

With the fast development of various wireless charging applications such as cell phones and electric vehicles, there is substantial interest in contactless power charging across an air gap. The contactless power transfer (CPT) system based on the resonance coupling method, which is composed of separate coils with the same resonance frequency, is feasible for exchanging energy within 2 m. However, generally, because the contactless charging system adopts a normal conducting wire, the size of the antenna is too large to be equipped to deliver a large amount of power promptly. From this point of view, we propose the combination of CPT technology with high-temperature superconducting (HTS) transmitter antenna, which we call the superconducting contactless power transfer (SUCPT). The superconducting transmitter antenna can deliver a mass amount of electric energy in spite of a small-scale antenna. The SUCPT technique is expected as a refined option to transfer a large amount of power and extend the distance. In this study, our research team achieved the improvement of transmission efficiency and extension of transfer distance using an HTS antenna in the inserted resonator coil between the HTS antenna and normal conducting receiver coils. We achieved improved transfer distance and quantity of about 25% compared with the normal conducting antenna under the same power conditions.

This study introduces 600-km/h wheel-type railway concept propelled by linear synchronous motor (LSM) and deals with the conceptual design for LSM system. The LSM is designed to be of a coreless type, which uses high- Tc superconducting electromagnet (SC-EM) as on-board field magnet. From tentative train parameters, we suggest a conceptual LSM model and its design parameters to achieve the train performances. As high- Tc SC material, we use currently available YBCO tape in designing the SC coil. We produce three SC coil models and estimate tentative design values of each model. The feasibility study described herein provides informative design ranges of LSM for 600-km wheel-type railway.

This paper describes the design and test of a high-Tc Superconducting (HTS) power conversion system with the GdBCO magnet and presents its operational characteristics through tests. The HTS power conversion system can be employed to charge and discharge an Energy Storage Magnet (ESM). The HTS power conversion system consists of two heaters, a transformer, and a GdBCO pancake magnet. The energy stored in the dc magnet is converted to ac power via a transformer consisting of an HTS secondary and a normal copper primary. The timing sequential control and thermal transition of heaters are important factors to generate charging and discharging in ESM. In this paper, we verified the feasibility of the HTS power conversion system and obtained the design and manufacturing techniques for scale-up of the system. Based upon the tests, the operating current of 12 A in the transformer and the heater current was optimally derived. The magnetic energy was stored about 46.7 J. In discharging test, the system was converted from dc to ac power at 0.5 Hz and 1 Hz. The efficiency of the system reached about 96%.

This paper introduces a novel flux switching synchronous generator (FSSG) using high-temperature superconducting (HTS) field coils. Unlike conventional superconducting synchronous generators, the HTS field coils in the proposed FSSG are mounted in the stator and do not rotate during operation. Therefore, the design and fabrication of the cooling and excitation systems for HTS field coils are easier than those for the conventional superconducting synchronous generator. To verify the feasibility of the structure, a 15 MW-class FSSG was designed using a fundamental design methodology considering the mechanical stress of the rotor core. The design methodology uses mechanical and electromagnetic equations. It defines the size of the rotor first using mechanical equations for the rotor and designs the HTS field winding and armature winding using the electromagnetic equations and an FEM analysis. In addition, the operational characteristics of the FSSG were analyzed by a transient motion analysis using the FEM program. This paper could be utilized to develop superconducting synchronous generators.

This paper presents a numerical analysis on MW-class high-temperature superconducting (HTS) synchronous generator, especially focusing on damper layer design. Our research program to develop a large-scale HTS wind turbine generator (WTG) core technology, a two-dimensional electromagnetic FEM model of the direct-drive HTS WTG, comprised of 24 air-core type HTS race track coils (24 poles), has been built. The damper is used for stable operation of HTS field coil against varying magnetic field by change of rotation speed. This model is designed to obtain basic operating parameters for HTS WTG, including magnetic field distribution and induced electromotive force, in static and transient condition. First, the parameters in static condition, which means that the rotating speed is constant, are compared with our design parameters to confirm the feasibility of our numerical analysis. Second, in transient condition, we focused on the reaction between rotating magnetic field and its stator components, damper, and armature winding. By changing damper material having different electrical conductivity and magnetic permeability, we concluded our damper design to be applicable to our MW-class HTS synchronous generator model.

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electrical vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power. However, it has obstacles to commercialize such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using HTS antenna in the WPT system, it is called as, superconducting wireless power transfer for electric vehicle (SUWPT4EV) system. Since the superconducting wire has merits a larger current density and higher Q value than normal conducting wire, the HTS antenna enables to deliver a mass amount of electric energy in spite of a small scale antenna. Thus, SUWPT4EV system has been expected as a reasonable option to improve the transfer efficiency of large electric power. Authors already demonstrated the efficienct effects for inserted resonator using simply copper tube wires, which structure is helix type of multi layers. In this study, as a practical approach, authors evaluated the SUWPT4EV system with inserted copper type resonator, which structure is a rectangular shape of single layer to reduce installation volume. Based on the evaluation results, authors deduced the practically alternative structure for the inserted resonator to reduce the installation space as well as to improve transmission power, compared with non-resonator SUWPT4EV system under radio frequency (RF) power of 370 kHz below 500 W.

The contactless power transfer (CPT) systems have been recently gaining popularity widely since it is an available option to realize the power delivery and storage with connector-free devices across a large air gap. Especially, the CPT with electromagnetic resonance coupling method is possible to exchange energy within 2 m efficiently. However, the power transfer efficiency of CPT in commercialized products has been limited because the impedance matching of coupled coils is sensitive. As a reasonable approach, we combined the CPT system with HTS wire technology and called as, superconducting contactless power transfer (SUCPT) system. Since the superconducting coils have an enough current density, the superconducting antenna and receiver coils at CPT system have a merit to deliver and receive a mass amount of electric energy. In this paper, we present the feasibility of the SUCPT system and examine the transmission properties of SUCPT phenomenon between room temperature and very low temperature at 77 K as long as the receiver is within 1.0 m distance.

We already fabricated a proto-type HTS charging system with photovoltaic (PV) system and obtained design parameters for DC converter and HTS charging system. In order to develop the real scale charging system efficiently, we suggested a maximum power point tracking (MPPT) controller using a perturb and observe (P&O) MPPT algorithm for PV system. In this paper, we designed and simulated the MPPT controller for the real scale HTS charging system. As well as, the PV module has been analyzed by solving solar cell equivalent equations. The simulated and theoretical results presented here are being considered the next study which addresses the design and fabrication parameters.

In terms of electrical energy, the technical fusion with solar energy system is promisingly applied in order to improve the efficiency in the power applications, since the solar energy system can convert an eternal electric energy in all-year-around. As one of such power applications, we proposed a current charging system for HTS magnet combined with solar energy (CHS). As this system can operate without external utility power to charge the HTS load magnet due to the solar energy, the operating efficiency is practically improved. The power converter, which is interfaced with solar energy and HTS magnet systems, plays an important role to transfer the stable electric energy and thus, the stabilized performance of the converter with solar energy system is one of essential factors. In this study, we investigated various charging performances under different operating conditions of the converter. In addition, operating characteristics have been analyzed by solving solar cell equivalent equations based on circuit simulation program.

We have been constructed a proto-type electromagnetic suspension (EMS) based maglev vehicle system. The maglev concept utilizes magnetic forces for noncontact suspension, guidance and propulsion. The suspension system with high temperature superconducting (HTS) hybrid electromagnet (EM) is composed of HTS coils and normal coils, which consume little power to keep large suspension gap. The magnetic forces realize to guide the vehicle, propel the vehicle along the guide-way and assist in braking action. The proto-type EMS-based Maglev model is designed to keep the suspension gap of 20 mm. This paper presents the theoretical analysis of the maglev vehicle based on the EMS model to obtain the designing parameters for levitation and propulsion forces. The magnetic field distributions of the electromagnetic forces with hybrid EM and propulsion stator coils are analyzed based on three dimension (3D) finite element method (FEM) analysis. From the simulation results, appropriately design parameters of the suspension, guidance and propulsion were obtained.

A technical fusion is an important option to establish renewal development in the mutual fields. We have proposed a novel superconducting power supply that is combined with superconducting power supply and solar energy system. An eternal electric energy can be converted by solar energy system, which contains solar panel, photovoltaic (PV) controller and energy-storing battery, can be utilized in the utility power of superconducting power applications. The novel power supply could operate without external utility power to charge the HTS load magnet due to the solar energy. We can improve the operating efficiency and install it in remote locations where utility power is not available. In this paper, as a first step of this work, we showed the possibility of technical fusion between a superconducting power supply and a solar energy system.

It has been widely established that gaseous helium (GHe) can be injected into a sub-cooled liquid nitrogen (LN2) cooling system to control the pressure of such a system because of its non-condensing characteristics. A sub-cooled LN2 cooling system is known as one of the most promising method to develop a large scale superconducting machine. Unfortunately, the electrical breakdown voltage of GHe is not good enough for developing a high voltage electric machine such as a superconducting fault current limiter (SFCL). To enhance the dielectric characteristics of current leads placed in GHe, the use of solid barriers is regarded as an efficient method. In this study, experiments are made on the dielectric characteristics of GHe and the barrier effects and results are analyzed in order to improve the dielectric performance of a high voltage SFCL using a sub-cooled LN2 cooling system. The dielectric experiments of the energized sphere and the grounded plane in GHe are examined according to various pressures with a solid insulating barrier. The dielectric experiments are performed by installing barriers made of glass fiber reinforced plastics (GFRP) between two electrodes and the electrical breakdown voltage according to the pressure of GHe and the position of a barrier is observed. As a result, it is found that the position of a solid barrier and the pressure of GHe are important in enhancing the dielectric characteristics of a sphere-to-plane electrode system with quasi-uniform field.