Ji-Kwang Lee

Design of HTS Magnets for a 600 kJ SMES

Development of a 600 kJ Superconducting Magnetic Energy Storage (SMES) system is in progress by Korean Electric Research Institute (KERI). High-temperature superconducting (HTS) wires are going to be used for the winding of the system. The design of the HTS windings for the system is presented in this paper. We considered BSCCO-2223 wire for the HTS windings. The operating temperature of the winding was decided to be 20 K which will be accomplished by conduction cooling method using cryo-coolers. Auto-Tuning Niching Genetic Algorithm was adopted for an optimization method of the HTS magnets in the SMES system. The objective function of the optimal process was minimizing the total amount of the HTS wire. We also estimated the AC loss which can be generated in the discharge period. These HTS windings are going to be applied to the SMES system whose purpose is the stabilization of the power grid

Stress Analysis of HTS Magnet for a 600 kJ SMES

Auto tuning niching genetic algorithm was used to design optimal HTS magnets for the 600 kJ class SMES system under several design constraint conditions. Constraint conditions were operation loss of magnet (less than 2 W), inductance of magnet (less than 24 H), the number of double pancake coils (about 10 DPCs), the number of turns of DPC (less than 300 turns), outer diameter of DPC (close to 800 mm) and total length of HTS wire in a DPC (less than 500 m). As a result of optimum design, we obtained design parameters for the 600 kJ SMES magnet according to two operating currents, 360 A and 370 A. However, even though the HTS magnet was designed optimally in respect to the electromagnetics, consideration of mechanical integrity due to the stress by Lorentz force must not be neglected for the stable operation of the SMES system. Therefore, we developed a program, through the finite element method (FEM), for stress analysis due to Lorentz force in operation of the SMES system. In this paper, the stresses (radial and hoop stress) imposed on the designed HTS magnets were calculated by the program, and the results of stress analysis were discussed.

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.

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.

Conceptual Design of HTS Magnet for a 5 MJ Class SMES

Superconducting magnetic energy storage (SMES) systems with High Temperature Superconducting (HTS) wires have been actively developed world-wide. A 600 kJ class SMES with Bi-2223 HTS wire has been in development as a national project since 2004 and is currently approaching the final testing stage of the first of three phases. In the second phase of the project, several MJ class HTS SMES will be developed. In this paper, designs of magnets for 5 MJ class SMES with DI-BSSCO and YBCO coated conductor are presented and compared.

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.

AC Loss and Thermal Stability of HTS Model Coils for a 600 kJ SMES

A 600 kJ superconducting magnetic energy storage system (SMES) project with high temperature superconductor (HTS) started as a national project in Korea. The HTS model coils were designed and fabricated for a preliminary test prior to the creation of a full scale prototype. Single reinforced BSCCO-2223 wires were used for the model coils and the operating temperature was decided to be 20 K. Even though an SMES is not an AC-powered device, time-varying currents during the charging and discharging periods lead to the generation of time-variation magnetic fields applied to the model coils and the generation of AC loss. In this paper, AC loss and the temperature distribution of model coils are analyzed and discussed.

Reduction Effect on Magnetization Loss in the Stacked Conductor With Striated and Transposed YBCC Coated Conductor

Recently, it is proposed to make striations on the YBCO coated conductor and to transpose each other as one of the solutions to decrease the perpendicular magnetization loss. For large power application using HTS, the stacked conductor packing the YBCO coated conductors should be used because the current carrying capacity of a single conductor is limited. The stacked conductor has different AC loss characteristics from single conductor because the screening currents in the adjacent conductors affect the local magnetic field at the position of each conductor in the stacked conductors. In this paper, we research the effect by the stack, striation and transposition on magnetization loss of YBCO coated conductors in perpendicular magnetic field. To estimate the reduction effects of perpendicular magnetization loss, several short samples as the stacked conductor with striation and transposition are prepared and tested. We compare the measured results of the conductors with that of the single YBCO coated conductor to estimate the reduction effects.

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.