Myungjin Park

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.

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.

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.

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.

Design of the Cryogenic System for 100 MVA HTS Transformer

A 100 MVA, commercial class high temperature superconducting (HTS) transformer was designed. In this paper the cryogenic system to extract the heat generated at the winding due to the AC loss and the heat penetration through the wall and the current lead and keep the winding temperature under design temperature is presented. The operation temperature is set at 67 K to increase the critical current and reduce the amount of HTS tape usage and the volume. The HTS winding was concentrically arranged to reduce the AC loss. The system consists of main cryostat with the windings and secondary cryostat with cooler, cryopump and the heat exchanger inside. The liquid nitrogen is entering the main cryostat at 65 K and assumed to be leaving at 67 K. The winding temperature distribution is simulated with the anticipated heat load using Fluent. The effect of the liquid nitrogen flow rate, inlet location is investigated and discussed.

Non-Contact Measurement of Current Distribution in Parallel Conductors by Using Hall Sensors

A parallel HTS conductor to flow large current is essential for applications of HTS power device. Non-uniform current distribution in the parallel conductor is caused mainly due to the difference of inductance. There are a contact method which measures current directly and a non-contact method which measure indirectly. But current distribution of each conductor in parallel conductors can not be measured with conventional method. In this paper, we researched a measurement method to identify current distribution of the parallel conductor indirectly with Hall sensors and compared with the analysis results by 2-D FEM.

Conceptual Design of a 5 MVA Single Phase High Temperature Superconducting Transformer

HTS transformers are being developed by one of 21st Century Frontier R&D Programs in Korea. The final target of the program for the HTS transformer is to develop a 3 phase 100 MVA HTS power transformer. Before then, we proposed a single phase 5 MVA HTS transformer using 2 G wires. It is not for commercialization but for the preliminary research for fabricating the 100 MVA HTS transformer. We supposed volt per turn of 100. It has primary, secondary and tertiary windings. Its size is almost same with that of a 33 MVA single phase HTS transformer in previous work. AC losses due to the winding methods and the variations of other parameters are analysed.