[Show abstract][Hide abstract] ABSTRACT: We have been developing a 1 MW, 1 sec UPS-SMES for the protection of production lines of an industrial plant or large-scale experimental devices such as a fusion device from a momentary voltage drop and an instant power failure. A conduction cooled prototype LTS pulse coil of 100 kJ class was developed as a key component of the UPS-SMES. The prototype coil has demonstrated excellent thermal characteristics during cooling and exciting tests. In this paper, measurements of the temperature in the coil during experiments and thermal analysis by using two-dimensional finite element methods were compared to clarify the high heat transfer properties of this prototype coil. This coil was wound with a NbTi/Cu Rutherford cable, which is extruded with aluminum. In order to realize the conduction cooled LTS pulse coil, FRP with polyethylene fibers (Dyneema FRP) and Litz wires were used as spacers. Dyneema FRP improves the heat transfer from layer to layer in the windings. Litz wires increase the heat transfer from turn to turn in the windings and enable conduction cooling of the coil by attaching the end of the Litz wires directly to the cold heads of the cryocoolers. It was clarified that these spacers were very effective and the coil has a large stability margin in terms of the design values
IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The output limit of the available power of a prototype conduction-cooled low temperature superconducting (LTS) pulse coil is clarified for the optimization of the coil. The winding conductor of this coil is a NbTi/Cu Rutherford cable, which is extruded with aluminum. Dyneema® fiber reinforced plastics (DFRP) and Litz wires are used as the spacers of this coil. A prototype coil with a stored energy of 100 kJ was successfully fabricated and tested, and the coil performed excellently. In this paper, the stability margin of this coil is clarified by thermal analysis, using a two-dimensional finite element method, taking into account the effects of both types of spacers, DFRP and Litz wires. Additionally, the maximum output power of the coil is estimated at about three times the rated output.
[Show abstract][Hide abstract] ABSTRACT: Interstrand contact resistances of Bi-2212 Rutherford cables for SMES coils were evaluated from a comparison between measured data and 2D-FEM analyses on interstrand coupling losses in these cables. The cables were composed of 30 non-twisted Bi-2212 strands with a diameter of 0.81mm and a cable twist pitch of 90mm. Three samples were measured; one of them had NiCr cores and the others had no cores. One of the latter two samples repeatedly experienced bending. The interstrand coupling losses were measured in liquid helium for the straight samples under transverse ac ripple magnetic fields superposed on dc bias magnetic fields. The transverse magnetic field was applied to the samples in directions both perpendicular and parallel to the flat face of the cable. The effect of the bending on the interstrand coupling losses could be neglected for the non-cored samples. The interstrand coupling losses of NiCr cored sample decreased by about 30% compared with the non-cored samples, in case the direction of the transverse magnetic fields applied to the cable is perpendicular to the flat face of the cable. Using these results and 2D-FEM analyses, taking into account that interstrand contact conditions vary from the center to the edge in the cross-section of cables, gave us the conclusion that the between side-by-side strands contact with metallurgical bond only in both edges of the cables.
Physica C-superconductivity and Its Applications - PHYSICA C. 01/2006; 445:1078-1082.
[Show abstract][Hide abstract] ABSTRACT: The stability of a prototype conduction-cooled LTS pulse coil for UPS-SMES of 100 kJ was evaluated. This coil has been developed as a first step of a project to develop a 1 MW, 1 UPS-SMES to protect semiconductor chip production equipment and nuclear fusion experimental devices, etc, from momentary voltage drop and power failure. The winding conductor is an NbTi/Cu Rutherford cable, which is extruded with aluminum. This conductor has both low AC losses and high stability under specified orientation of changing transverse magnetic fields. The 100 kJ-coil are wound by the new winding method. In order to improve the heat conduction properties in the coil, Dyneema FRP and Litz wires are used as spacers. Litz wires were connected with the cryocooler as cooling paths. On the pulse operation, the operating current is reduced from 1000 A to 707 A in 1 s. In this paper, the thermal properties of the 100 kJ-coil are calculated by finite element method under pulse operation. In order to estimate the stability, a calibration experiment was carried out. Results indicated that our prototype LTS pulse coil has high stability to enable to allow over 10 times as large heat as AC losses.
IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We are planning to develop a 1 MW, 1 sec UPS-SMES for a protection from a momentary voltage drop and an instant power failure. As the first step, we have been developing a 100 kJ class prototype UPS-SMES, using a low temperature superconducting coil because of its better cost and performance over the high temperature superconducting coil. However, the difficulty to utilize a pool-boiling LTS pulse coil is the reliability of operation. To solve this problem, a conduction-cooled LTS pulse coil has been designed and fabricated as a key component of the UPS-SMES. The reduction of AC loss and high stability are required for the SC conductor for the conduction-cooled coil because of a limited cooling capacity. The SC conductor of a NbTi/Cu compacted strand cable extruded with an aluminum is designed to have the anisotropic AC loss properties to minimize the coupling loss under the specified orientation of the time varying magnetic field. The coil was wound with a new twist-winding method in which the variation of twist angle of the conductor was controlled with the winding machine designed specifically for this purpose. The fabrication technique and performance of a conduction-cooled prototype LTS pulse coil are described.
IEEE Transactions on Applied Superconductivity 01/2005; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have been developing the UPS-SMES as a protection from momentary voltage drop and power failure. The superconducting system is suitable as electric power storage for large energy extraction in a short time. The most important feature of superconducting coil system for the UPS-SMES is easy handling and maintenance-free operation. We have selected low temperature superconducting (LTS) coils instead of high temperature superconducting (HTS) coils from the viewpoint of cost and performance. However, it is difficult for the conventional LTS coils to fulfill maintenance-free operation since the cooling methods are either pool boiling with liquid helium or forced flow of supercritical helium. Thus, a conduction cooled LTS pulse coil has been designed as a key component of the UPS-SMES. The development program of 1 MW, 1 sec UPS-SMES is explained.
IEEE Transactions on Applied Superconductivity 07/2004; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In order to develop the 100 kJ class UPS-SMES as a protection from momentary voltage drops, design of the conduction cooled LTS pulse coil was carried out and special winding machine has been developed. Such coil is required to simultaneously attain low AC loss and high stability and the distributions of temperature in the coil are sensitively controlled. For this purpose, an aluminum stabilized conductor with circular cross-section composed of a Cu stabilized NbTi Rutherford cable was used as the winding conductor, and in the winding process the twist angle of the conductor around its axis was controlled to adjust the direction of edge-on orientation to the Rutherford cable to direction of local transverse magnetic fields applied to the conductor in winding area of the coil. The developed winding machine is used for this winding method. As a result, conduction cooled LTS pulse coil can be expected to operate stably in adequate temperature margin.
IEEE Transactions on Applied Superconductivity 07/2004; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In our previous paper, we proposed a new method for designing compact stranded superconducting conductors as a solution to the dilemma that low loss and high stability could not be simultaneously attained in commonly used conductors. By adjusting the twist pitches and directions of the sub-cables in the conductor, inter-sub-cable coupling losses in it are decreased. As a result, not only the total coupling loss in the conductor is decreased, but also high stability is maintained due to the low contact resistance between the sub-cables. The fundamental performance of the conductors designed using our method has been confirmed through measurements of the coupling loss and the minimum quench energies in the conductor. Our measurements are, in this case, carried out using Rutherford cables with strands instead of the conductors with sub-cables. The results obtained successfully show the validity of our new design method.
[Show abstract][Hide abstract] ABSTRACT: Electrical loss-measurements were carried out in liquid nitrogen for long Bi-2223 tapes wound into a solenoidal-coil under various external conditions of ac transport currents and ac magnetic fields. In this experiment a new measuring-system, which is an extension of our original measuring-system applicable to short and straight HTS tapes, was developed. In this new system, the Poynting vectors at the outer and the inner surfaces of the sample coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil; The moving direction is the coil axis and its distance is one pitch of coil windings. Several samples were prepared in order to clarify fundamental electromagnetic-properties of Bi-2223 coils with various windings. The obvious difference of loss properties among these samples was observed for some external conditions of ac transport currents and ac magnetic fields.
[Show abstract][Hide abstract] ABSTRACT: A new electrical system was developed for measuring ac losses of long HTS tapes or wires wound into a solenoidal-coil. This coil-loss measuring-system is an extension of our original ac-loss measuring system that is applicable to short, straight HTS tapes under various external conditions of transport currents and transverse magnetic fields, and is useful for fundamental studies of various windings of practical multi-layered coils. In this new system, the Poynting vectors at the outer and the inner surfaces of the coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil. The moving direction is the coil axis and its distance is one pitch of coil windings. The value of ac losses can be obtained by summation of the Poynting vector at many positions during the movement. The applicability of this system was confirmed by ac loss measurements on a solenoidal-coil wound loosely with Ag-sheathed, multifilamentary Bi-2223 tapes.
IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new winding method was proposed to reduce ac losses in stable LTS pulse coils. The suitable conductor for this winding method is a multi-layer type conductor composed of stacked Rutherford type cables with low resistive contact between strands. In this winding method, the twist angle around axis of the conductor is controlled during winding process to adjust the direction of edge-on orientation to stacked cables to direction of local magnetic fields applied to the conductor in winding areas. Inter-strand coupling losses in this coil are expected to be small in spite of low resistive contact between strands in the wound conductor. In order to clarify the effect of this winding method, firstly, a test conductor was fabricated and ac losses in short samples of the conductor were measured. This was an aluminum stabilized conductor, and a Rutherford cable composed of 8 Cu/Nb-Ti strands was used as the core of this conductor. The loss is measured with the transverse magnetic fields applied either perpendicular or parallel to the broad cable face, the "face-on" (FO) and "edge-on" (EO) orientations, respectively. From observed data, it is found that EO loss is 0.12 times FO loss . Secondly, ac losses in test coils wound with this conductor were calculated. The result showed that this winding method was very effective.
IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new method for designing compact stranded superconducting conductors is proposed as a solution to the dilemma that low loss and high stability cannot be simultaneously attained in the commonly used conductors. In our design, the twist directions of the conductor and those of the sub-cables in it are the same. In addition, the twist pitch of the sub-cables is relatively longer than that of the conductor. The sub-cables crossover each other in the conductor. Under the changing transverse magnetic fields oriented perpendicular to the broad face of the conductor, the induced voltages between the above-mentioned crossover sub-cables become small, so inter-sub-cable coupling losses are decreased. As a result, not only the total coupling loss in the conductor is decreased, but also high stability is maintained due to the low contact resistance between the sub-cables. Our method theoretically indicates such high performance as attaining both low ac loss and high stability. An example of our design is shown for a large-scale compact stranded superconducting conductor.
TEION KOGAKU (Journal of the Cryogenic Society of Japan) 01/2003; 38(6):285-290.
[Show abstract][Hide abstract] ABSTRACT: Measurements of minimum quench energy (MQE) of a new type Rutherford cable were carried out. This cable has low resistive paths located near each edge of cable's cross-section, enabling quick transfer of transport currents from one strand to other strands when a part of normal state appears locally in the strand. In addition, this cable has relatively longer strand twist pitches in relation to the cable twist pitches so as to decrease coupling losses in the cable under changing transverse magnetic fields with face-on orientation. In order to evaluate the effect of current transfer on cable stability, measured MQE were compared with numerically calculated values for a single strand. Measured MQE was greater than 18 times the calculated single strand value (18 strands in our cable). This indicates that current transfer between strands effects MQE of our cable. And our cable has almost the same MQE per unit volume as standard Rutherford cable without stainless steel cores. Thus we confirmed that our Rutherford cable has high stability.
Physica C Superconductivity 01/2002; 378:1154-1157. · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new winding method was proposed for fabrication of high performance coils wound with Bi-2223 tapes, which have anisotropy of both critical-current and magnetization-loss properties depending on direction of applied magnetic fields. In the winding process, continuous control of twist angles around tape axes is adopted to reduce face-on oriented magnetic fields applied to the wound tape in coil operation. For an example of large-scale solenoid coils cooled at 77, 66 or 20 K, great improvement of the current capacity was theoretically predicted. This result implies that compared to the old coil, and under identical operating currents, the new type coil would allow a great reduction in the amount of Bi-2223 tapes needed. It was also shown theoretically that a one-order reduction of magnetization losses could be achieved. A preliminary experiment was carried out on the fundamental problem of the strain effect of twisting and bending tapes on the critical current, and the observed data suggested that the effect can be neglected.
Physica C Superconductivity 01/2002; 372:1402-1405. · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new type of high temperature superconducting wire with
transposed filaments is fabricated and tested to confirm reduction of
transport current losses. Sample wires of 1 meter long are made of four
Bi2223 multifilamentary pre-tapes which are wrapped spirally into two
layers around the silver core wire without any insulation. The wrapping
direction and pitch for the two layers can be changed easily so that
both the opposite and the same direction wires are prepared for the
present experiment. The sample parameters are chosen to achieve uniform
distribution of transport currents inside the opposite-direction wire.
These wires, obtained after heat treatment, have relatively high
critical currents of 99-122 amperes in liquid nitrogen in no external
magnetic fields. In the range of currents higher than a half of the
critical current, the observed hysteresis loss due to ac transport
currents in the opposite-direction wire is about 60% as large as that in
the same-direction one. This experimental result for the loss reduction
agrees closely with our theoretical prediction
IEEE Transactions on Applied Superconductivity 04/2001; · 1.20 Impact Factor