Masao Morita

Improvement of a claw pole motor using additional ferrite magnets for hybrid electric vehicles

This paper presents a design and experimental study of a rare-earth less motor for hybrid vehicles. Claw pole motor was chosen for base topology and additional ferrite magnets are installed into the rotor poles in order to increase high torque capability and to reduce low field excitation loss. Some design criteria, test results and comparison with Nd-Fe-B magnet motor are shown.

Design parameters influencing non-uniform current distributions in superconducting multi-stage stranded cables

We have suggested that non-uniform currents occur due to certain design parameters, for example a combination of cabling pitches, in a previous study. In the present study, we evaluate the occurrences of non-uniform current distributions in terms of design parameters, i.e., the combination of cabling pitches, winding methods (solenoidal and pancake winding) and cross-sectional shape of the cable by numerical analyses. Finally, some basic design concepts to solve this problem are proposed.

Designing stable and high-current density rotor windings of superconducting generator

A method to statistically predict quench training characteristics of a rotor windings of a superconducting generator is presented. In the method, energy of a disturbance due to a conductor motion and a quench current is statistically estimated. The authors apply this method to a rotor of the 70 MW class superconducting generator being developed in the Super-GM project and study the dependence of the stability on parameters of the rotor conductors, such as amount of copper stabilizer, accuracy of conductor dimensions and operating current density. To predict the stability, compliance of the rotor winding pack is a key parameter and estimated by a finite clement method. In the study, it is shown that there is an optimum value of ratio of copper to superconductor to maximize the current density of the winding pack keeping necessary stability. Based on the study, a designing method for stable and high current density rotor winding is discussed.

Normal propagation velocity and quench energy of the rotor model for a 70 MW class superconducting generator

A rotor model was fabricated to estimate the performance of the 70 MW class superconducting generator. The normal propagation velocity and quench energy for the rotor model in the rotational field are measured at various rotating speeds. An analytical model is proposed in order to explain the experimental data. In the calculation, the heat transfer and the temperature rise of liquid helium in the rotational field are considered. The calculated results are compared with the experimental data, and these agree well. Therefore it becomes possible to precisely design field windings of superconducting generator.

Numerical analyses for ramp rate limitation from the standpoint of heat generation during current redistribution [in superconducting cables]

The ramp rate limitation (RRL) must be improved for large applications, for instance fusion machines. In superconducting multi-strand cables, adding to the coupling loss, the heat generation during current redistribution (moderation of a nonuniform current) causes temperature rises. Especially for cables in conduit-type conductors (CICC), the relation between the heat capacity of the coolant and the total heat dissipation determines the temperature rise. When this rises above the current sharing temperature, the conductor must quench. To establish stability against nonuniform current distribution, a small contact resistance between strands is preferable. However a smaller contact resistance results in a larger inter-strand coupling loss. Therefore, the contact resistance must be optimally designed to prevent the cable from RRL. In this study, the authors analyzed the current redistribution in a three-strand cable with electrical contact between strands. The heat generation due to: (1) normal resistance; (2) contact resistance between strands; and (3) terminal joint resistance were evaluated in the cases of a variety of contact resistances and cooling conditions. Finally, some of the particular phenomena reported as being found in experiments with multi-strand cables were simulated by analyses and then discussed.

The Superconducting Properties for La–Sr–Cu–O Systems

Superconducting oxides, La–Sr–Cu–O and Y–Ba–Cu–O were prepared using nitrate mixture by spray dry method and/or oxide and carbonate powder mixtures followed by pressing and sintering. The superconducting properties such as critical temperature (Tc) and critical current density (Jc) were measured by resistive and inductive methods, and transport current and magnetization measurements, respectively. The Tcs(the resistive offset) were 32, 91 K for La and Y system, respectively. The Jc(77K) of 1,840 A/cm2 was observed for Y system by transport current measurement.

Cryogenic and electrical performance at a factory test of a rotor for 70 MW class slow-response excitation type superconducting generator

70 MW class superconducting generators are under development as a national project in Japan. This is an eleven-year program which commenced in 1988. The manufacturing of the slow response excitation type rotor was completed at the beginning of 1996, and performance test of the rotor was carried out in the factory at the beginning of 1997. The factory test has been completed successfully. This paper describes the factory test results of the cryogenic performance and the electrical performance.

Fundamental characteristics of a claw pole motor using additional ferrite magnets for HEV

This paper presents a specification of a claw pole motor that has a field excitation coil for hybrid electric vehicles. The characteristic of the claw pole motor is no use of Dy and Tb which can increase torque capability. The filed excitation which can be generated by controlling filed current in a rotor provides us controllable efficiency. Additional ferrite magnets are installed between the rotor poles for the purpose of increasing torque capability due to moderating magnetic saturation of each claw. FE analysis and experimental results are shown in this paper.

Quench characteristics of rotor winding of superconducting generator in static and rotating conditions

Previously, we have developed a theory to statistically estimate the training characteristics of a superconducting coil considering stresses to the conductor, structure of the cross section and mechanical properties of the conductor. In this paper, we estimate quench characteristics of the rotor windings for the superconducting generator in static and rotating conditions of the rotor by applying our theory, and compare the theoretical data with the experimental results. The theory explains the experimental results.

Nb/sub 3/Sn superconducting coil for AC use

Nb/sub 3/Sn superconductors were developed for AC use, and a coil was fabricated. The Nb/sub 3/Sn superconductors were manufactured using the internal diffusion process. To reduce AC losses, the spacing between Nb filaments was designed to be 0.5 mu m; consequently, the space factor of Nb filaments was 6%. The diameter of a strand was 0.2 mm, and the diameter of a Nb filament was 0.4 mu m. AC losses in the strand were 180 kW/m/sup 3/ at 0.5 T (60 Hz, peak value). A coil was made using the wind-and-react method using conductors composed of 7*7 strands. The Specifications of the coil were an inner diameter of 156 mm, an outer diameter of 188 mm, a height of 34 mm, and a number of turns of 17 turns*4 layers. To reduce wire motion, the coil was impregnated with epoxy resin. The quench current for DC operation was 1280 A, and the maximum magnetic field of the conductors was 1.6 T. Coil degradations were not observed. The magnet was tested under AC 60-Hz operation. The quench current was 340 A (r.m.s.). The cause of quenching is thought to be the temperature rise of the conductors due to coupling losses among the strands.