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A load line method has been used to calculate the critical current of superconducting magnets. However, in high-temperature superconducting tapes that have a rectangular cross section, as the critical currents vary depending on the direction of an external magnetic field, the load line method cannot be used to precisely calculate the critical currents of the HTS magnets because it cannot fully consider the magnetic anisotropy of the HTS tape. In nested HTS magnets that have multiple layers, calculating the critical current considering the magnetic anisotropy is very time consuming. This paper presents an efficient calculation method to calculate the critical current of nested HTS magnets. The secant method and the fixed-point iteration method are used to reduce the calculation time. The critical currents of two nested HTS magnets are calculated: a double magnet consisting of a YBCO inner coil and a BSCCO outer coil and a triple magnet consisting of a YBCO inner coil, a YBCO middle coil, and a BSCCO outer coil. The calculation results demonstrate that it is possible to very effectively calculate the critical current of nested HTS magnets by using a combination of the secant method and the fixed-point iteration method.

Open-type current sensors have been commonly used for DC motor controller, AC variable controller and Uninterruptible Power Supply. Recently they have begun to be used more widely, as the growth of renewable energy and smart-grid in power system. Considering most of the open-type current sensors are imported, developing the core technology needed to produce open-type current sensors is required. This paper describes the development and test results of open-type current sensors. Design of C type magnetic core, selection and test of a Hall sensor, design of current source circuit and signal conditioning circuit are described. 100A class DIP(Dual In-line Package) type and SMD(Surface Mount Devide) type open-type current sensors was made and tested. Test results show that the developed open-type current sensor satisfies the accuracy requirement of 2% and linearity requirement of 2% at 100 A of DC and AC current of 60Hz. Temperature compensation was carried out by using a temperature compensation circuit with NTC(Negative Temperature Coefficient) thermistor and the effect of the temperature compensation are described.

태양광 모듈 효율의 증가를 위해 렌즈나 반사판 등을 이용한 집광 시스템 개발이 활발하게 진행되고 있으며, 집광장치는 일반적으로 렌즈를 사용하거나 고집속비의 광학장치를 이용하여 태양광 추적형으로 설계하여 고집속화를 추구하고 있다. 그러나 집속비에 비례하여 열로 소산되는 에너지 밀도가 증가하므로, 고집속에 따른 태양전지 온도상승에 의한 태양전지 효율 저하를 방지하기 위해 집광장치의 냉각에 유의해야 한다. 본 논문에서는 이러한 여러 가지 제약 조건을 피하여, 저가격의 반사형 광학장치를 이용한 경제적인 저집광형 태양광 모듈 시스템을 연구 개발하였다. 일반모듈에 저집광장치를 사용하여 태양광 모듈의 발전효율을 증대 시키면서 집광으로 인해 발생하는 열을 냉각장치를 통해 방출하였다. 제안된 저집광형 냉각장치(MCS, Micro Cooling System)의 특징은 모세관력에 의한 자연 순환 방식으로서 외부 동력원이 불필요하며, 유체 상변환시의 잠열을 이용함으로써 고성능 냉각 구현이 가능하다. 117W 태양광 모듈에 반사판을 설치하고 냉각장치가 있는 모듈과 냉각장치가 없는 모듈을 비교 하였다. 냉각장치를 설치한 모듈에서의 발전량이 28% 증가하였다. 【To increase the efficiency of a solar module, the development of solar concentrator using a lens or reflection plate is being proceeded actively and the concentrator pursues the a concentration using a lens or an optical device of a concentration rate and designing as a solar tracking system. On the other hand, as the energy density being dissipated as a heat according to the concentration rate increases, the cares should be taken to cool the solar concentrator to prevent the lowering of efficiency of solar cell by the increasing temperature of the solar cell. This study, researched and developed an economical concentrator module system using a low priced reflection optical device. A concentrator was used as a general module to increase the generation efficiency of the solar module and heat generated was emitted by the concentration through the cooling system. To increase the efficiency of the solar concentrator, the cooling system was designed and manufactured. The features of the micro cooling system (MCS) are a natural circulation method by the capillary force, which does not require external power. By using the potential heat in the case of changing the fluid, it is available to realize high performance cooling. The 117W solar modules installed on the reflective plate and the cooling device in the cooling module and the module unit was not compared. The cooling device was installed in the module resulted in a 28% increase in power output.】

This paper examined the properties of an high-temperature superconducting (HTS) magnet, such as the Ic-B relation and critical current, with pancake windings of a 12-mm-wide Zr-doped HTS tape. Considering the width of the Zr-doped HTS tape was 12 mm, which was three times wider than that of a conventional 4 mm tape, the current distribution at the cross-section of the 12-mm tape was assumed to be non-uniform. The HTS magnet consisting of four pancake windings of the 12-mm tape was chosen as the model for calculations and measurements. The inner diameter and the number of turns of the pancake winding were 30 mm and 88 turns, respectively. When the critical current of the HTS magnet was calculated assuming the same critical current for all pancake windings, the critical current of the whole magnet was limited by the middle pancake windings. The limiting of the magnet current by the middle pancake windings was due to properties of the Zr-doped HTS tape. After allocating the pancake windings with higher critical current to the middle part of the HTS magnet, the critical current was limited by the top and bottom pancake windings.

The critical current of the HTS(High Temperature Superconductor) tape is governed by cooling temperature, magnetic field and its angle to HTS tape originated from its geometrical structure. At the HTS coil design stage, the critical current of the coil is calculated by considering the Ic-B characteristics of the 2G tape and the operating current is determined based on the critical current. The operating current and the structure of the 5 T coil are suggested through the FEM (Finite Elements Method) analysis and calculation. As a part of our on-going research on a 20 T LTS/HTS magnet, we have designed and constructed a 5 T HTS insert coil and tested it in liquid helium temperature.

This paper describes the operation characteristic of a single-phase PFC converter with 1-switch voltage doubler strategy for single-phase double-conversion UPS. A single-phase PFC converter with 1-switch voltage doubler strategy needs a diode bridge and one bidirectional active switch. Thus it is possible to reduce the material cost. However, the study results of operation characteristic and controller design has not been known after the converter circuit was proposed. For the performance evaluation of PFC converter, single-phase 3kVA double-conversion UPS was tested. The performance of PFC converter is experimentally confirmed with followings - input current reference traking, input power factor correction.

In a High temperature superconducting (HTS) tape with high aspect ratio, the magnetic field applied to the HTS tape can be different considerably within the HTS tape. The current distribution in the HTS tape is generally non-uniform becauthe current distribution is strongly se dependent on the applied magnetic field. Non-uniform current distribution in a HTS tape has not been properly considered when the critical current has been estimated. This paper shows the calculation of critical current of a HTS magnet consisting of pancake windings. Non-uniform distribution of current in the HTS tape is considered during the calculation of the critical current. Results of calculation show the current concentrated in the middle part of the HTS tape which is used for one pancake winding. self 1. INTRODUCTION A number of superconducting machines are being developed, such as, SMES (Superconducting Magnetic Energy Storage), NMR (Nuclear Magnetic Resonance), MRI (Magnetic Resonance Image) and magnetic separator [1-3]. Superconducting magnets are used for most of the superconducting machines. To guarantee the cryogenic stability of the superconducting magnets, it is important to estimate precisely the critical current of the superconducting magnets. In a HTS tape which is used for the HTS magnet with high aspect ratio, the magnetic field applied to the HTS tape can be different considerably within the HTS tape. The current distribution in the HTS tape is generally non-uniform because current distribution is strongly dependent on the applied magnetic field. In order to estimate the critical current of the HTS magnet, it is needed to consider the non-uniform distribution of the current in the HTS tape. Non-uniform current distribution in HTS a tape has not been considered when the critical current has been estimated . Current distribution in a HTS tape has been studied in some papers [4, 5].

In order to investigate the AC loss of the multilayer conductor in a high temperature superconductor cable, a voltage-lead was generally attached to the outermost layer of the conductor. But the conductor’s AC loss has not been completely cleared due to the various contact positions and arrangements of the voltage-lead. In this paper, we prepared a semi-triple layer conductor consisting of an inner layer and an outer layer with double layer structure. To measure the AC loss of the conductor, two voltage-leads (inner-lead, outer-lead) were soldered to the wires in each layer and arranged along their surfaces, as well as another voltage-lead (total-lead) was soldered to the inner layer and arranged on the surface of the outer layer. The results show that the AC losses for each layer measured from the inner-lead and the outer-lead, respectively, are identical to the sum of the wire losses. The AC losses in the semi-triple layer conductor measured from the total-lead and the outer-lead are identical for the uniform layer current density, and similar to the sum of the wire losses in both layers. However, the losses measured for the non-uniform layer current density from three voltage-leads are unequal to each other, and the loss from the total-lead significantly differs from the sum of the wire losses.

In this paper a robust voltage controller for a single-phase UPS inverter is newly presented. The voltage controller is designed using -based robust control scheme to simultaneously guarantee robust stability and robust tracking performance in the presence of load variations. Firstly the robust performance of the resulting controller is theoretically confirmed via -analysis. Then simulations and experiments for the single-phase inverter system with linear and nonlinear loads demonstrate feasibility of the proposed control method providing improved performance - good regulation and fast dynamic response.

When the aspect ratio of a magnet varies, the magnetic field in the magnet also varies. The critical current of a tape-shaped HTS wire varies with the direction and magnitude of applied magnetic field. Consequently when the aspect ration of a HTS magnet varies, the critical current of a HTS magnet varies. This paper shows the relation between the aspect ratio of a magnet and the energy and inductance of a HTS magnet. The critical current is also shown at various aspect ratio of the magnet. The length of the HTS wire, inner diameter of the magnet, and number of pancake are chosen to be variables which varies the shape of the magnet. For a HTS magnet consisting of pancake windings, calculation results show the number of pancake windings are the prime factor which varied the energy and inductance of the magnet. The inner diameter of the magnet varies the energy and inductance of the magnet a little.

When the length of wire used to make an HTS magnet is fixed, the magnetic properties of the HTS magnet including the central magnetic field and stored energy mostly depend on the aspect ratio of the HTS magnet. This paper presents calculations of the magnetic properties of a BSCCO HTS magnet at various aspect ratios. The HTS magnet was assumed to be made by pancake windings. The total length of the BSCCO wire was varied from 2 to 10 km. For a specific length of the BSCCO wire, the number of pancake windings was varied up to 70. The inner diameter of the HTS magnet was fixed to be 50 mm and 77 K. When the length of the BSCCO wire was 2 km, the central magnetic field was maximum when 34 pancake windings were used. The maximum central magnetic field and the current of the HTS magnet were 859.3 mT and 21.8 A, respectively. The number of turns of a single pancake winding and the aspect ratio of the HTS magnet were 171 turns and 2.54, respectively.

In a magnet with pancake windings, inserting a gap between the pancake windings can increase the central magnetic field. This paper shows the optimized length of each gap is able to maximize the central magnetic field. Inserting a gap also improves field uniformity because the pancake windings are spread across a wider area. A high temperature superconducting (HTS) magnet consisting of BSCCO-2223 pancake windings was chosen for the calculation model to show the effectiveness of the proposed method. The E-J relation was used to determine the critical current, and an evolution strategy was adopted for the optimization of gap length. The results of calculations show that the critical current and the central magnetic field increased by 86.0% and 33.7%, respectively, for a magnet consisting of ten pancake windings.

In order to electrically investigate the AC losses of the conductor and the shield in an actual HTS cable with shield, we attached two voltage-leads to the conductor and shield of a short cable which is the same as the Korea Electric Power Corporation (KEPCO) HTS cable under the field test, and examined it. The result shows that the polarities of the loss voltages measured from both voltage-leads are opposite. The ratio (1.6) between the losses for different transport periods measured from the conductor-lead is quite large. It is considered from these results that the conductor loss is the sum of the losses measured from the conductor-lead and shield-lead. And this conductor loss corresponds well with the numerical result too. Moreover, the total loss of the short cable measured from the proposed electrical method at 77 K was compared with that of the KEPCO cable by calorimetry at 66.6 K through our numerical model. The difference between the measured losses and numerical ones is almost the same. This means that the shield loss is measured from the shield-lead, and the conductor loss from both voltage-leads.

This paper proposes embedded System of two wheeled inverted pendulum robot designed by model based design method, using MATLAB/SIMULINK and LEGO NXT Mindstorms. At first, stability and performance of controller is verified through modeling and simulation. After that direct conversion from simulation model to C code is carried and effectiveness of controller is experimentally verified. Two wheeled inverted pendulum robot has basic function about autonomous balancing control using principle of inverted pedulum and it is also possible to arrive at destination. In this paper, state feedback controller designed by quadratic optimal control method is used. And quadratic optimal control uses state feedback control gain K to minimize performance index function J. Because it is easy to find gain, this control method can be used in the controller of two wheeled inverted pendulum robot. This proposed robot system is experimentally verified with following performances - balancing control, disturbance rejection, remote control, line following and obstacle avoidance.

Magnetic field and Electric field of High Temperature Superconducting magnet are very important to analysis of superconducting magnet. The maximum perpendicular magnetic field was applied to the outermost pancake windings. The critical current of all the magnet windings is limited by the critical current of the outermost pancake windings. The E-J relation was used to determine the critical current, and an evolution s trategy was adopted for the optimization of gap length between each pancake windins. The results of calculations show that the critical current and the central magnetic field and uniformity increased by 82.6% and 31.6% and 50.8%, respectively, for a magnet consisting of ten pancake windings. This paper did an analysis the cause of increase the critical current and central magnetic field and uniformity in no gap and optimal gap model.

The effects of a gap at a high temperature superconducting magnet which has an insert magnet and an outsert magnet are examined. Both magnets consist of pancake windings. The optimum gap of an insert magnet and an outsert magnet are calculated by using the response surface method. The insert magnet consists of 8 YBCO pancake windings. The number of turns of a pancake winding and the inner diameter of the insert magnet are 60 turns and 40 mm, respectively. The outsert magnet consists of 12 BSCCO-2223 pancake windings. The number of turns of a pancake winding and the inner diameter of the outsert magnet are 100 turns and 115 mm, respectively.

In this paper, embedded control system of segway robot using model based design is presented. Design of control program in embedded system can be implemented simply and easily by model based design method using MATLAB/SIMULINK. Segway robot is consisted of a NXT Mindstorms controller, two DC servo motors, a ultrasonic sensor, a gyro sensor, and a light sensor. It is a unstable nonlinear system and has a control problem of body pitch angle. So controller of segway robot is designed using state feedback LQR control. It is confirmed through design and experiment of controller that the model based design method, that is not depend on target processor, has merits compared with the text based design in aspects such as a program development, an error detection/modify, and an insight of software structure.

In a high temperature superconducting magnet consisting of pancake windings, the perpendicular magnetic field considerably reduces the value of the critical current of the outer pancake windings due to anisotropy. An air gap was inserted between each pancake winding in this paper to reduce the decrement of the critical current in each pancake winding. In a low temperature superconducting magnet, the central magnetic field decreases when there is an air gap between the pancake windings. On the other hand, the central magnetic field of a HTS magnet increases when an air gap is provided. The properties of the HTS insert/outsert magnet having an air gap between the pancake windings are examined in this paper. YBCO wire and BSCCO wire were used in the insert and the outsert magnets, respectively. An E - J relation and the evolution strategy were adopted to calculate the optimum critical currents of both magnets. The calculation results showed that there was an optimum air gap which maximized the central magnetic field. The optimum air gap was dependent on the specifications of the HTS magnet.

In an HTS magnet consisting of pancake windings, an air gap between the pancake windings can be used to increase the central magnetic field because the air gap increases the critical current of pancake windings. The effects of an air gap on the central magnetic field of an HTS magnet are discussed in this paper according to the various number of turns and also to the number of pancake windings. Results of calculation show the air gap could increase the central magnetic field and the field uniformity simultaneously. The optimum air gap which maximized the central magnetic field was about 4 mm at eight pancake windings and 50 turns per pancake winding. The central magnetic field increased 6.2% from 0.225 T (no air gap) to 0.239 T (4 mm air gap) at that case.

Due to the anisotropy of a tape-shaped HTS wire, the method to determine the operating current of an HTS magnet needs to be different from that of a LTS magnet. This paper presented estimation of the critical current of pancake windings excited by multiple power sources. Critical currents were determined by using field dependent E-J relation. A new method to define the magnetic field of the HTS wire has been proposed in this paper. Calculated critical currents of pancake windings were compared with measured ones of the HTS BSCCO magnet consisting of 10 pancake windings. Effects of multiple power excitation on the increment of the central magnetic field has been also described. Test results showed the estimated critical currents of pancake windings agreed well with that of measured ones and the central magnetic field was increased at multiple power excitation by 28.4% comparing with that of single power excitation.

HTS pancake windings have been commonly used for the insert coil of high field magnets. All pancake windings have been connected in series and excited by a single power source. In that case, currents of the whole pancake windings were limited by the minimum current of the top and the bottom pancake windings where maximum perpendicular magnetic field was applied. This paper proposed the multiple power excitation of the HTS magnet which consists of pancake windings. It was able to increase the magnetic field of the magnet by conducting critical currents to all pancake windings. Results of calculation by using a model BSCCO magnet shows that proposed method was able to generate higher magnetic field comparing with the conventional single power excitation.

When the HTS magnet consisting of pancake windings is excited by a single power source, most of the pancake windings operate under their critical currents because currents of the entire pancake windings are limited by the critical current of the pancake winding which has the lowest critical current. By using multiple power sources, all pancake windings are able to conduct their critical currents. This paper describes the HTS magnet with pancake windings which are excited by multiple power sources. Critical current of each pancake winding is determined by using optimization technique. Fabrication of the BSCCO magnet consisting of 10 pancake windings is described and test results of the BSCCO magnet are given. The magnetic field and the perpendicular magnetic field of the magnet excited by multiple power sources are compared with those of the magnet excited by a single power source.

A cylindrical high temperature superconductor (HTS) is often used in power applications such as power transmission cables and matrix fault current limiters. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density and one hollow conductor made of Bi-2212 bulk material. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analysed. The results show that the measured losses for all the conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with high critical current density is in good agreement with the numerically calculated one based on the polygon model, whereas the loss measured for the Bi-2223 conductor with low critical current density coincides with the calculated loss from the monoblock model.

Pancake winding and solenoid winding are commonly used ones in superconducting power transformers. This paper deals with AC losses of the pancake winding and solenoidal winding made of YBCO wire. The pancake winding and the solenoidal winding which had same number of turns and diameter had been made and tested. Inner diameter and number of turns of both windings were 100 mm and 30, respectively. Pancake winding and solenoidal winding which were made of BSCCO wire were also fabricated and measured. Results of measurements were compared with the AC losses obtained by numerical calculation.

The multi-stacked wires which are made of one type of wires, YBCO wires or BSCCO wires, are being currently used in superconducting machines. Property of hybrid multi-stacked (HMS) wire made of the combination of YBCO wire and BSCCO wire can be different from the uniform multi-stacked (UMS) wire. This paper presents the magnetization losses of HMS wires which were made of YBCO wires and BSCCO wires. HMS 2 stacked (YB) wire and HMS 4 stacked (YYBB, YBYB, YBBY and BYYB) wires were tested. Y and B stand for YBCO wire and BSCCO wire, respectively. The YBCO wire and the BSCCO wire which had similar width were chosen to fabricate the UMS wires and HMS wires. The losses of the HMS wires were compared with the loss of UMS wires. According to the measurement results of the HMS 2 stacked wire and HMS 4 stacked wires, the loss of HMS wire was between the loss of UMS BSCCO and UMS YBCO wire at low magnetic field and it was almost the same with those of UMS BSCCO and UMS YBCO wire at high magnetic field.

AC loss is one of the major topics in large AC power applications using high temperature superconductor such as power transformers, transmission cables and fault current limiters because it is closely related to operation efficiency. Multi-stacked tape conductors should be used to transport the large current in those power applications. A research of various arrangements of HTS tapes for multi-stacked tapes has been performed to increase the capacity of transport current in HTS power applications. In this paper, we studied magnetization loss and shield effect from several different arrangements of BSCCO tapes such as Face-to-Face type, regular matrix type (mtimes2) and irregular matrix type. The results show that the magnetization loss of the Face-to-Face arrangement was lower than those of the other matrix types for the same stacking numbers. We think that the result was due to the shield effect by demagnetization of adjacent HTS tapes which were located as face to face

AC losses generated in the HTS winding differ from that of the short sample because each turn of winding is magnetically affected by adjacent turns. In this paper, we calculated the AC loss of HTS pancake windings. Numerical calculation was carried out to figure out the magnetic field in the windings. During the AC loss calculation of both windings, AC losses were obtained by using the short sample AC losses data. According to the results of calculation, loss calculation by using the short sample data of multi-stacked tape was more approached to winding loss than that by using the single tape data. To prove the effectiveness of the calculations, AC losses of windings was measured and compared. Finally the single phase HTS transformer with multi-stacked tape was constructed and tested.

For large power application using high-T/sub c/ superconducting (HTS) tape, parallel face-to-face stacked tape conductor should to be used because single tape is limited in flowing of demanded large current, also, appropriate distance between tapes in stacked tape conductor is needed for high voltage insulation. The stacked tape conductor has different characteristics compared with single tape because of screening effect. In general situation, HTS tapes are used by winding in coil shape, so, magnetic fields generated in the coil are operated as external fields and have various direction to each tape in the coil. In this paper, we research the magnetization loss in stacked tape conductor exposed to external magnetic fields having various direction and compare measured results of stacked tape with those of single tape, and we also present influences of insulation thickness between tapes in stacked tape conductor by comparison to the measured results for noninsulation stacked tape. We solve the magnetization loss in stacked tape conductor by finite element method to examine the experimental results.

For large power applications, such as, HTS transformer, HTS motor and HTS power cable, stacked HTS tapes should be used because single HTS tape is limited in flowing of demanded current. Besides, insulation between layers is need for safe operation because high voltages are applied in those applications. The stacked HTS tapes have different characteristics compared with the single HTS tape because of screening effect. In this paper, we measured the magnetization losses in stacked HTS tapes of several samples having the various insulation thickness and various packing numbers of tape at 77 K. Properties of three different types of the stacks which consisted of 2, 3, and 4 tapes were measured and compared with that of single HTS tape. Also, numerical calculation by finite element method was done to compare with experimented data. Perpendicular magnetic fields were applied to the HTS stacks as external magnetic field. Results of measurement and calculation showed that magnetization loss of a stacked tape divided by stacking number of tape was smaller than the single tape's loss. This tendency was distinct as the distance between the tapes became closer and stacking number of tapes increased.

Motors with HTS wires or bulks have been developed recently. These are a large synchronous motor with HTS wires at the field winding in the rotor, hysteresis and reluctance motors with HTS bulk in the rotor. This paper presents the fabrication and test results of an HTS induction motor. Conventional end rings and short bars were replaced with HTS wires in the motor. Stator of the conventional induction motor was used as the stator of the HTS motor. Rated capacity and rpm at full rotor of the conventional motor were 0.75 kW and 1710 rpm. Two HTS wires are used in parallel to make the end rings and bars. The critical current of the BSCCO-2223 HTS wire which was used in the bars and end rings were 115 A. An electrodynamometer was coupled directly to the shaft of the rotor with HTS wires.

This paper described construction and test results of a 10 kVA HTS transformer. Three phase transformer with double pancake windings were constructed. BSCCO-2223 wire, silicon sheet steel core and FRP cryostats were used in that transformer. After the test of basic properties of the 3 phase HTS transformer using no load test, short circuit test and full load test, continuous operation of 100 hours with pure resistive load has been carried out. Test results proved overload capability and reliability of the HTS transformer.

One of the major issues in power application of the HTS transmission cable is the AC loss as it is related with power transmission capacity and efficiency. Although the HTS transmission cable has only transport current without external magnetic field, the magnetization loss as well as the transport current loss is generated because any tape constituting transmission cable is exposed to magnetic fields given by currents flowing in other tapes of cable. The magnetic field induced by layer flowing current in the transmission cable have two components, that is, axial component magnetic fields at inner region and azimuthal component at outer region of each layer for transmission cable axis due to winding structure of cable. Therefore, any tape in the cable experience parallel and axial component magnetic field for tape wide face. So, the magnetization loss must be calculated in consideration of this field configuration.

The superconducting transmission cable is one of the interesting parts in power application using high-temperature superconducting tape. An important issue in HTS transmission cable is AC losses because it is related with power transmission efficiency and the capacity of cryo-cooler in the case of operating below liquid nitrogen temperature. In power transmission cable, although it experiences no external field, any tapes constituting the transmission cable are exposed to magnetic fields given by currents flowing in other tapes of cable. Therefore, we think that magnetization loss as well as transport current loss is generated in transmission power cable. The magnetization loss has to be considered for cable design and efficiency estimation because it is about 30–50% of transport current loss in our calculation results.

In superconducting power machines, such as transformers and motors, an external magnetic field is applied to the superconducting wire. When the external magnetic field is applied to the superconducting wire, coupling loss is generated in the normal metal stabilizer. This paper describes the calculation of the coupling losses of the round HTS wires by the finite element method. Effects of filament arrangement and filament size of the round HTS wire are considered. Three types of filament arrangement (single layer, double layer and honey comb arrangement) are considered. Calculation results show that coupling loss of the single layer arrangement is the smallest among the three cases.

The superconducting transmission cable is one of interesting part in HTS power application using high temperature superconducting tape. One important parameter in HTSC cable design is a transport current sharing because it is related with a current transmission capacity and a loss. The current sharing is decided by cable length (inductance) and resistance (by joint and AC losses). The AC loss in power transmission cable is studied only transport current loss. But, although it is applied no external field, any tapes constituting transmission cable are experienced magnetic fields given by currents flowing in other tapes of cable. In this paper, the authors calculate current sharing for each layer of a 4-layer cable. The transport current loss and magnetization loss for various cable length considering the twist of each layer are also studied.

Bi-2223 tapes have been developed for low-field power applications at liquid nitrogen temperature. When the Bi-2223 tapes are used in an application such as a power transmission cable or a power transformer, they are supplied with an AC transport-current and exposed to an external magnetic field generated by neighboring tape's AC currents simultaneously. AC loss. taking into account such real applications. is a crucial issue for power applications of the Bi-2223 tapes to be feasible. In this paper, the transport losses for different AC current levels and arrangements of the neighboring tapes have been measured in a 1.5 m long Bi-2223 tape. The significant increase of the transport losses due to neighboring tape's AC currents is observed. An increase of the transport losses caused by a decrease of the Bi-2223 tape's critical current is a minor effect. The measured transport losses could not be explained by a dynamic resistance loss based on DC voltage-current characteristics in combination with the neighboring tape's AC currents. The transport losses do not depend on the frequency of the neighboring tape's AC currents but its arrangements in the range of small current especially.

This paper describes the construction and test results of a 10 kVA single phase HTS transformer. Double pancake windings with BSCCO-2223 HTS tape and GFRP cryostat with room temperature bore are used in the transformer. Two double pancake windings are connected in series to provide 94/spl times/2 turns and two double pancake windings are connected in parallel to conduct the secondary current of 45.4 A. Coefficients of the constructed transformer are obtained using fundamental tests of the transformer. According to the test results, a slightly larger leakage reactance than expected is observed due to the bulky core which surrounded the cryostat.

A superconducting induction generator (SIG) with two rotors is presented. The two rotors are called inner rotor and outer rotor, respectively. The inner rotor is located inside of the outer rotor and free to rotate. The inner rotor consists of an HTS winding and iron yoke. The outer rotor is made of a copper shell. It is driven by a mechanical power source. The outer rotor rotates at higher angular velocity than that of the rotating magnetic field generated by the stator current while the inner rotor rotates at the same angular velocity with the field made by the stator current. The HTS winding produces enough magnetic field to compensate the reactive armature current, which improves the power factor of the generator close to unity. A 1.5 kVA SIG was manufactured and tested to realize the concepts of the HTS free inner rotor. Good electrical characteristics were shown by experiment. Due to the simplified structure of the inner rotor cooled with LN/sub 2/, the SIG presented in this paper can be realized as a medium-sized generator, as well as a large one and used as a supplemental power source connected to a conventional power system.

A single-phase power transformer with windings made of T/sub c/ superconducting tapes was fabricated and tested. The tapes are made of Bi-2223 imbedded in a silver alloy matrix. The primary and secondary windings are made of double pancake coil. The rated voltages of the windings are 220/110 V. Four pancake type coil windings are stacked on the core. The inner two act as the primary winding. Fundamental characteristics are obtained through short circuit and no load tests. The overload capability and characteristics are investigated.