Mitsugi Yamaguchi

A study on performance improvements of HTS coil

It is of great concern for magnet designers to address their critical currents at a given field and bore size. In the case of high temperature superconducting magnets wound with BSCCO Ag-sheathed tapes, they have a strong magnetic anisotropy and therefore the critical current of magnets defined by an average voltage drop over an entire coil cannot be easily determined like low temperature superconducting magnets. An analytical way to obtain the critical current of HTS magnets is described by means of the electric and magnetic field analyzes based on the measured data of BSCCO Ag-sheathed tapes. A performance improvement of HTS magnet is studied by pursuing an optimum coil cross section.

Angular dependence of E-J characteristics and dissipative properties in Bi-2223/Ag tape

We study the angular dependence of E–J characteristics and dissipative properties due to thermal disturbance in the Bi-2223/Ag multifilamentary tape in the low-voltage region. In order to simulate the dissipative properties, we take into account the analytical expressions of the E–J characteristics as a function of temperature, external magnetic field and field direction, which agree well with the experimental data. It is shown that the simulation results of the dissipative properties agree with the experimental data semi-quantitatively. The relationship between the current sharing rate and its contribution to the temperature increase is also discussed, based on the simulation. These results are crucial for high-Tc superconducting power application systems with a persistent current mode where even low-power dissipation is detrimental to the performance.

Numerical evaluation of AC loss in high temperature superconducting coil

An approximated method to estimate the electro-magnetic AC loss in high temperature superconducting coil was proposed. We applied this method to estimate the AC loss characteristics of the high temperature superconducting coil made by stacking pancake coils which are wound by Bi2223/Ag tape. The analytical AC losses of the HTS coil were compared with the measured AC losses before and after impregnation by epoxy resin obtained in the previous work by National Institute of Advanced Industrial Science and Technology. The analytically estimated electro-magnetic AC losses in the HTS coil were much smaller than the measured AC loss of the coil. The AC loss characteristics could not be explained by the method proposed in this paper. The main reason of this discrepancy was considered that the measured AC losses in the HTS coil contained large amount of the mechanical AC loss due to the AC vibration of the winding even if the HTS coil was impregnated.

Theoretical and experimental study on AC loss in HTS tape in AC magnetic field carrying AC transport current

AC loss characteristics of high temperature superconducting tape in external AC magnetic field carrying AC transport current were theoretically and experimentally studied. We measured the AC transport current and magnetization losses in a conventional Bi2223/Ag multifilamentary tape in the external AC magnetic field carrying the AC transport current. The measured AC magnetization loss, AC transport current loss and total AC loss were compared with the numerical results. The measured AC loss characteristics of the tape can not be explained by the critical state model. Numerical calculations on the AC losses in the tape were performed by using our analytical model introducing the electric field and current density relation locally determined in the filamentary region of the tape. The numerical losses by our model reasonably agree with the measured data.

Performance evaluation of high temperature superconducting coil

Abstract The current–voltage characteristics of Ag-sheathed Bi-2223 tape for high-temperature superconducting coils are measured as a function of the magnetic field and its flux angle to the tape at liquid nitrogen temperature. The approximate characteristic equations on critical currents and n values are obtained from this result. Then, the electric field distribution inside the coil can be calculated with the approximate characteristic equations. The current–voltage characteristics of high-temperature superconducting coil are analyzed and compared with the test result of conduction-cooled coil, producing relatively good agreements. The coil performances can be made clearer with the assistance of characteristic equations at the coil design stage and, further, the optimum coil design will be made possible.

Study on open gradient magnetic separation using multiple magnetic field sources

A new type of open gradient magnetic separator using multiple magnetic field sources was proposed. As an example, a open gradient magnetic separation using quadrupole magnetic field was focused in this paper. Simulation study was performed to investigate the basic separation characteristics of our separation method by analyzing the dynamic behavior of magnetic particles. The simulation results show that the continuous separation of paramagnetic particles of several tens micrometer diameter is enough feasible. We demonstrated the validity of proposed method by an experiment using quadrupole electromagnet.

Application of single DC reactor type fault current limiter as a power source

This paper presents an application of single DC reactor type fault current limiter (FCL) with a gate turnoff (GTO) thyristor bridge as an emergency power source. A DC reactor type FCL stores electrical energy in a superconducting coil at a steady state. When a power transmission stops due to line faults, the FCL supplies stored energy to the load. This conception can be realized by operating the GTO thyristor bridge as an inverter. On the other hand, the function of fault current limitation is possible by keeping all GTO thyristors turned-on. The proposed FCL is numerically tested in a three-phase distribution system.

A single DC reactor type fault current limiting interrupter for three-phase power system

The authors propose a single DC reactor type fault current limiting interrupter (FCLI) for a three-phase power system. The device uses a single high temperature superconducting (HTS) coil that operates in conjunction with a modified half control bridge composed of thyristors and diodes connected to a transformers secondary windings. One variety is an automatic interrupter, which automatically blocks fault current through the application of DC bias current to the bridge. Another is a gate interrupter, which does the same thing by locking the thyristors gate pulses. The authors examine the results of various simulations on a new device that both limits and interrupts fault current in a three-phase power system.

Numerical evaluation of measured AC loss in HTS tape in AC magnetic field carrying AC transport current

Numerical study to evaluate the validity of the measurement method of AC loss in high temperature superconducting tapes in external AC magnetic field carrying AC transport current was done. The AC transport current loss and the magnetization loss in a conventional Bi2223/Ag-sheathed multifilamentary tape in the external AC magnetic field carrying the AC transport current were measured by the four terminal method and the pick-up coil method respectively. Numerical calculations on the AC losses in the tape were performed by using our previously developed analytical model. The measured losses were compared with the analytical results and the errors of the AC loss measurement were evaluated.

Three-phase fault current limiter with one DC S/N transition element

The authors developed a DC S/N transition type three-phase fault current limiter, the primary element of which, is made of the superconducting bulk material, Bi-2223. This element is connected to secondary windings of transformers, through a modified half control bridge. This unique, single element device simultaneously limits and interrupts fault current, in three-phase power systems. This paper describes the results of tests, using a small scale model and simulation results.