Jun Takehara

Optimal design of tank shield model of transformer

A tank shield model of a transformer which is proposed by the Investigation Committee of IEE of Japan is analyzed. This is a model having the constraint that the maximum eddy current density should be less than a specified value. The automatic 3D mesh generation technique for hexahedral element is investigated for the optimal design of such a model. It is shown that reasonable results that satisfy the specified constraints can be obtained using Rosenbrocks method within the acceptable CPU time. The experimental verification is also carried out.

Finite element analysis of inrush currents in three-phase transformers

A new method for analyzing inrush currents in transformers is conceived by modifying the finite element method. Using this method, the detailed behaviour of the transient flux can be analyzed taking into account the residual magnetism and three-dimensional leakage flux. The new method is especially effective in the calculation of the inrush currents of three-phase transformers. The inrush currents are examined experimentally by using a new method for measuring the residual magnetism and an equipment which controls switching angles.

3-D optimization of design variables in x-, y- and z-directions of transformer tank shield model

By using the automatic 3-D mesh generation technique using hexahedral elements, which is applicable when design variables are changed in x-, y- and z-directions, a transformer tank shield model is optimized. The volume of tank shield can be considerably reduced by using the Rosenbrocks method (RBM) compared with the previous result having design variables in one direction. It is shown that the determination of initial values for RBM using the experimental design method (EDM) is indispensable for the practical application of the optimization method to obtain a desired result within an acceptable CPU time.

3-D finite element analysis of coupling current in multifilamentary AC superconducting cable

A method for analyzing the 3-D coupling current which is induced by an AC magnetic field in a multifilamentary superconducting cable is developed. In this method, such a superconducting cable, in which many twisted filaments are embedded in a matrix, is treated as macroscopic, having anisotropic conductivity. The method for treating the anisotropy of conductivity and the 3-D finite-element formulation are presented. The effectiveness of the technique is illustrated by the analysis of the 3-D coupling currents of superconducting cables. >

Metalorganic molecular beam epitaxy of III-V compounds using tertiarybutyl-V as group-V sources

Abstract This paper reports metalorganic molecular beam epitaxy of GaAs and InP on GaAs(100), and GaP on Si(100) using TBAs and TBP as group-V sources and TEGa and TMIn as group-III sources. It is found that the growth of GaAs is dominated by thermal decomposition of TEGa, while the growth of GaP and InP is influenced by both the reacting group-III and the phosphorus species. The hole concentration of the GaAs epilayers grown at 300 K decreases from 7.9×10 18 to 3.4×10 18 cm −3 with increasing substrate temperature, presumably due to a decrease in sticking coefficient of alkyls. PL spectra from the epilayers at 4.2 K show dominant emissions due to transition between free electrons and acceptors, which is in agreement with the electrical results.

Numerical and experimental investigations of current distribution at the joint between AC superconducting cable and normal conducting plate

The effect of the configuration of the joint between an ac superconducting cable and a normal conducting plate on the current distribution and the joule loss is investigated by using the 3-D finite element method. It is shown that the concentration of current can be reduced by changing the configuration of joint. The effectiveness of the analysis is verified by measuring the current distribution on the surface of a copper plate and the quenching current.

Study on Design of Superconducting Transformer with Amorphous Core Immersed in LHe

A simple and compact superconducting transformer with low loss amorphous core, of which both core and windings are immersed in liquid helium, is investigated. It is shown that the dimension of the new-type superconducting transformer is considerably smaller than those of conventional superconducting transformer and normal conducting transformer. Experimental investigation is also carried out.

3-D Analysis of Coupling Current in Large Capacity AC Superconducting Cable and Current Distribution at Joint with Normal Conducting Terminal Plate

A new method for analyzing 3-D coupling current which is induced by an ac magnetic field in a multifilamentary superconducting cable is developed. Its effectiveness is shown by comparing coupling loss calculated with measured one. The cause of quenching at the joint between a superconducting cable and a normal conducting terminal plate is clarified by analyzing 3-D current distribution at the joint.

Metalorganic molecular beam epitaxy of III–V compounds for solar cell application

Abstract This paper reports the metalorganic molecular beam epitaxy of GaAs, InP, and GaP using TBAs and TBP as group-V sources and TEGa and TMIn as group-III sources. It is found, that the growth of GaAs is dominated by thermal decomposition of TEGa, while the growth of GaP and InP is influenced by both the reacting group-III and phosphorus species. The GaAs epilayers grown using cracked TBAs show p-type conduction with hole concentrations being varied in the range of 7 × 10 16 − 1.7 × 10 19 cm −3 at 300 K as the cracking temperatures varied from 1300 to 1700°C. The hole concentration increases with the cracking temperature above 1450°C, suggesting that the carbon incorporation process is influenced by the reacting arsenic species from thermally cracked TBAs.