Gueesoo Cha

Comparison of AC losses of HTS pancake winding with single tape and multi-stacked tape

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.

Test and characteristic analysis of an HTS power transformer

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.

Optimum design of linear synchronous motor using evolution strategy combined with stochastic FEM

The random based evolution strategy (ES) in conjunction with stochastic finite element method (SFEM) is applied to the optimum design of electromechanical devices. (1+1) ES is adopted as an optimization method. Optimum pole shape is designed to increase the levitation and propulsion forces of the linear synchronous motor (LSM) which is used in a Maglev vehicle. The SFEM analyzes performance uncertainty due to the uncertain system parameter in the devices. The degree of randomness of objective function value is expressed by its expectation and variance. The optimization process is influenced by these values. To show validity of the proposed algorithm, results of ES combined with SFEM are compared with those of the conventional ES.

Development of a HTS squirrel cage induction motor with HTS rotor bars

Efficiency at full load and starting torque at starting are basic performance criteria of the induction motor. Conventionally deep bar or double cage bar have been used to increase the efficiency and starting torque of the induction motor. Effective resistance of the deep bar and double cage differs from starting to full load operation. To increase the efficiency and starting torque, HTS tapes can be used as the rotor bars. The resistance of HTS tapes develops at starting because of large starting current which exceeds the critical current of the HTS tape and it vanishes as the speed builds up. This paper presents the construction and test results of a HTS induction motor. End rings and short bars were made of HTS tapes. Stator of the conventional induction motor was used as the stator of the HTS motor. Rated capacity of the conventional motor was 0.75 kW. Performances of the HTS induction motor were compared with those of the conventional motor with same volume and specification. Test result showed that the speeds of the HTS induction motor were the same with synchronous speed up to 2.6 Nm and 1788 rpm at 9.7 Nm. It guarantees the high efficiency of the HTS motor. Starting torque of the HTS motor was more than twice of the conventional motor.

Test of an induction motor with HTS wire at end ring and bars

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.

Computation of three-dimensional electromagnetic field including moving media by indirect boundary integral equation method

We present a general analysis method for three-dimensional (3-D) eddy current problems with a moving conductor. The indirect boundary integral equation method (IBIEM) is employed for 3-D electromagnetic field problems including an arbitrarily shaped conductor with constant relative velocity. Since the 3-D motion effect is taken into account in the fundamental Greens function for the governing equation of diffusion type, this approach gets rid of spurious oscillations which usually occur in solutions obtained by the Galerkin finite element method. That is, the proposed method uses an elaborate fundamental Greens function for magnetic diffusion instead of artificial upwind techniques of the finite element method. In addition, a new accurate integration technique for very local functions related to the Greens function for magnetic diffusion is adopted, a technique that plays an important role in accuracy and stability of numerical solutions. The electromagnetic field and eddy current at any point are calculated through the numerical integration of the equivalent magnetic surface sources obtained by the integral system equation. The proposed method is numerically tested and validated through the analysis model where a conducting slab under a fixed rectangular coil moves with a constant velocity.

Effect of the stack in HTS tapes exposed to external magnetic field

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 tapes loss. This tendency was distinct as the distance between the tapes became closer and stacking number of tapes increased.

AC loss calculation of a multi-layer HTS transmission cable considering the twist of each layer

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.

Magnetization Loss and Shield Effect in Multi-Stacked Tapes With Various Stacking Configurations

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

Magnetization loss in HTS stacked tapes by various directional external magnetic fields

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.