Naoki Maki

Development of 70 MW class superconducting generators

This paper describes recent progress in an 11 year project for research and development (R&D) of 70MW class superconducting generators in Japan. Three types of 70MW class superconducting generators (called model machines) have been developed. Two slow response excitation type rotors were completed and rotational excitation tests of them were conducted at each factory A quick response excitation type rotor is in manufacturing and static excitation tests have been conducted at the factory. Also, the characteristics of a stator, which is to be commonly used for three rotors at the verification test facility, were measured by combining with one of the slow response excitation type rotors at the factory Test run for verification tests on the first machine has been started in May 1997 Tests on the other two model machines will follow the test on the first one.

Aluminum-stabilized superconductor and superconducting coil, and method of manufacturing the superconductor

Disclosed is a superconductor which has an aluminum area at the center of the cross section of the superconductor and a copper-covered multifilamentary NbTi composite conductor at the periphery parts of the cross section formed around the aluminum area, wherein the cross-sectional area ratio of (Cu+Al)/NbTi is in the range of 0.5 to 3.0 and the cross-sectional area ratio of Al/Cu is in the range of 0.05 to 0.5.. The superconductor is provided by a method comprising a first step of providing a superconductor-copper composite hollow body in which copper films are applied around the superconductors, a second step of area reducing the composite hollow body, a third step of heat treating the body, a fourth step of inserting an aluminum body into the hollow of the hollow body, a fifth step of subjecting the body to working such as drawing, a sixth step of subjecting the body to working such as twisting, forming or the like, with an additional area reduction being carried out, if necessary, subsequent to the third step. A superconducting coil is made using the superconductor, and the coil is used for a magnetically levitated vehicle or a nuclear magnetic resonance apparatus.

Electrical properties of superconducting joint between composite conductors

To investigate the electrical properties of the joint between superconducting multifilamentary wires, the authors used a radio-frequency superconducting quantum interference device (RF-SQUID) voltmeter to measure the extremely small voltage induced across the joint. They measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the picovolt range was obtained with this apparatus. Comparisons of current decay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux-creep-like phenomenon was seen in the current decay for the cold-welded and spot-welded joints.

Design and Component Development of a 50 MVA Superconducting Generator

This report describes the design, mechanical characteristics and key components of a 50 MVA, 3600 rpm superconducting generator.

Electromagnetic force and eddy current loss in dynamic behavior of a superconducting magnetically levitated vehicle

A magnetically levitated vehicle is being designed to travel between Tokyo and Osaka in about 1 h at a 500-km/h speed. When the car runs at a high speed, it moves laterally and vertically from its balanced position at low frequencies. The authors present calculations of electromagnetic forces and eddy currents generated in the onboard cryostat containing the superconducting magnet as a result of these motions. They show that the electromagnetic forces, eddy current losses and damping constants of the motion, especially for the lateral and vertical motions, depend on the materials of the radiation shield and the inner vessel in the magnet and change with the frequencies of car motion. The magnitudes of forces, losses, and damping constants in lateral motion are compared with those in vertical motion. To evaluate these quantities, numerical calculations were performed with a two-dimensional finite-element method.<<ETX>>

Quench analysis of superconducting magnet systems

A computer program QUENCH-M, which is applicable to the quench analysis of various superconducting magnet systems, has been developed. The program was applied to some typical systems. The authors discuss the circuit calculation of quench analysis for superconducting magnet systems. The graphical outputs of voltage and temperature distributions within superconducting coils were shown to be very useful for understanding the quench process. This program was found to be very useful for estimation of the maximum voltage during quench, because the maximum voltage is estimated not only from the resistance of the normal zone, but also from the voltage distribution within the coil. >

On-board power supply system of a magnetically levitated vehicle

A possible on-board power supply system for a magnetically levitated train is presented and its obtainable electrical power is estimated. The system uses special superconducting magnets, which are used only for generating electrical power. Some induction coils to pick up high-frequency components are set in front of the magnets. The special superconducting magnets and the induction coils will be mounted only at the head car and the tail car out of 14 cars in a train. The estimation shows that it is possible to obtain more than 630 kW of electrical power. >

Test results of 50 MVA superconducting generator

A 50 MVA superconducting synchronous generator with a superconducting field winding was developed. This paper describes its features and test results. The saddle-shaped field winding, impregnated with epoxy resin, was mounted on a torque tube and fastened with prestressed non-magnetic stainless steel wires. A free convection cooling system, which uses the thermosiphon effect, was adopted for the field winding. Cooldown of the rotor was carried out with a constant liquid helium feed rate of 50 l/h and it was completed smoothly within about 40 hours. After that, the rotor could rotate stably at 3600 rpm. Electrical tests of no-load, short-circuit and sudden short-circuit characteristics were also carried out. Finally, the 50 MVA generator was connected to a power network and confirmed to operate successfully for 80 minutes as a syncronous condenser with a small capacity.

Superconducting Rotor Development for a 50 MVA Generator

A superconducting rotor for a 50 MVA generatoi with a superconducting field winding was developed. This paper describes rotor development, and field winding static and rotating rotor excitation tests. Two electromagnetic damper shields, one for ambient temperature and the other for low temperature (50 K), were used to protect the field winding from time varying flux. The thermal strain that occurs between field winding supports and outer parts of the rotor body when a winding is cooled was prevented by providing individual supports for the winding and rotor body at one end of the rotor. The field winding was a concentrated saddle-shape type, inpregnated by epoxy. The rotor was tested using a small stator with an air gap armature winding. An output of voltage of about 1.5 kV and current of about 1.5 kA was obtained when a generating test was carried out at 3000 rpm.

Field winding model test of 70 MW class superconducting generator

A national project for development of a superconducting generator has been continuing since 1988 in Japan. In this project, the authors have been developing a superconducting field winding. An aluminium stabilized double standard superconducting cable has been developed for the winding. In the rotor, the centrifugal force field is 5000 G, and consequently liquid helium has a cooling ability ten times larger than that in the 1-G gravitational field. Therefore, a cryostable winding design can be used. A field winding model having 40% of the 70-MW-class generator field winding was tested in a nonrotated cryostat. The specification and structure of the cable and the test results are outlined.<<ETX>>