Jin-Ho Han

Characteristic tests of a 1 MVA single phase HTS transformer with concentrically arranged windings

A 1 MV A single phase high temperature superconducting (HTS) transformer was manufactured and tested. The rated voltages of primary and secondary of the HTS transformer are 22.9 kV and 6.6 kV respectively. BSCCO-2223 HTS tape was used for HTS windings of 1 MV A HTS transformer. In order to reduce AC loss generated in the HTS winding, the type of concentric arrangement winding was adopted to a 1 MV A HTS transformer. Single HTS tape for primary windings and 4 parallel HTS tapes for secondary windings were used considering the each rated current of the HTS transformer. A core of HTS transformer was fabricated as a shell type core made of laminated silicon steel plate. And a GFRP cryostat with a room temperature bore was also manufactured. The characteristic tests of 1 MV A HTS transformer were performed such as no load test, short circuit test and several insulation tests at 65 K using sub-cooled liquid nitrogen. From the results of tests, the validity of design of HTS transformer was ascertained.

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.

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.

Persistent Current Mode Operation of A 2G HTS Coil With A Flux Pump

A flux pump is a kind of power source that energizes superconducting magnets usually embedded in the cryogenic system. Therefore, heat loss through current leads is eliminated, allowing for more efficient cooling design. A winding technique, the so-called “wind-and-flip,” had been proposed by the authors to realize a jointless HTS coil for a perfect resistanceless closed loop, which may enable to induce a persistent current in an HTS coil wound with second-generation HTS tape. In this paper, we investigated charging/discharging characteristics and a possibility of persistent current operation of a jointless HTS coil with a flux pump. Results are discussed with regard to current capacity and temporal stability with a prototype jointless HTS coil.

Analysis of perpendicular magnetic fields on a 1 MVA HTS transformer windings with flux diverters

In high temperature superconducting (HTS) transformer with double pancake windings, the perpendicular component of leakage magnetic flux density (B/sub r/) applied to HTS tapes of double pancake windings is larger than that of solenoid windings, which acts as a cause to decrease the critical current in HTS tape and increase AC loss. In this paper, in order to reduce the B/sub r/ applied to HTS windings, the use of ferrite flux diverters is presented. Flux diverters are located in between the primary windings and the secondary windings, and must be made of low-loss materials to minimize the heat. And electromagnetic analysis of a single-phase 1 MVA 22.9 kV/6.6 kV HTS transformer with flux diverters in HTS windings was accomplished. The variation of B/sub r/ applied to the secondary windings and magnetic flux density in flux diverters were analyzed by changing their relative permeability of flux diverters respectively. Suitable relative permeability of flux diverters to reduce B/sub r/ applied to HTS windings was selected, considering flux diverter losses by increment of B in flux diverters.

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.

Characteristic test of a 1 MVA single phase HTS transformer with pancake windings

A 1 MVA single phase high temperature superconducting (HTS) transformer was fabricated and a part of experimental test for characteristics of the transformer was performed. The rated voltages of primary and secondary of the HTS transformer are 22.9 kV and 6.6 kV respectively. BSCCO-2223 wire was used for HTS windings whose shapes are double pancake arranged reciprocally. Single HTS wire for primary windings and 4 HTS wires for secondary windings were used considering the rated current of the transformer. Four HTS wires in secondary windings were transposed at the connection between double pancakes 3 times. The electrical insulation and transport current test were performed at 77 K using liquid nitrogen. The rest of the test for the characteristics of the transformer is in progress.

Analysis of AC losses in HTS pancake windings for transformer according to the operating temperature

AC loss is one of the most important parameters in high-temperature superconducting (HTS) ac devices. Among the HTS ac power devices, the transformer is the essential part in the electrical power system. But unfortunately, the transformer is the worst device concerning ac loss because of very large magnetization loss due to high magnetic field applied to the HTS wire. We calculated the magnetization losses in HTS pancake windings for transformer according to the operating temperature. Two kinds of arrangements of HTS pancake windings were adopted for calculation of ac loss of shell-type transformer, and the analysis results were presented and discussed.

The Optimal Design of 600 kJ SMES Magnet Based on Stress and Magnetic Field Analysis

In the development of large scale superconducting magnetic energy storage (SMES) systems, the problem of mechanical stresses induced in the windings by Lorentz force becomes more critical as dimensions of system and magnetic field increase. In this paper, an optimal design process of a 600 kJ SMES magnet combined with mechanical stress analysis is presented. A stress analysis method based on electromagnetic finite element analysis (FEA) is explained in detail. The results of the analysis led to the development of an optimum design, electro-magnetically and mechanically, of a single-pole double pancake coil (DPC) type 600 kJ SMES magnet. The stress in each DPC are described along with recommendations for winding tension in the manufacturing process to minimize radial and hoop stress in each DPC.