In this special edition the results of a national project on the development of superconducting generators (SCGs) are reported. Before these reports, the history of developing conventional generators, (that is, a larger generator needs higher technology for cooling) motivation for developing SCGs (which is on way of better cooling technologies for larger generator), key technologies of SCGs except superconducting technology, features of SCGs, (that is, larger capacity, small size, high efficiency, good characteristics for power system operation and so on, ) present situation of the development and some comments of real application are described.
A 70MW class model superconducting generator was designed, manufactured, and tested from 1988 to 1999 as phase I. This was a national project on applications of superconductive technology to electric power apparatuses that was commissioned by NEDO as part of the New Sunshine Program of AIST, MITI. And phase II is now being carried out in the same formation as phase I. A 70MW class model superconducting generator had been developed to establish technologies for the 200MW class pilot generator in phase I. The world's highest output (79MW), the world's longest continuous operation (1, 500 hours), and other excellent characteristics have been achieved on a 70MW class model superconducting generator, and the key technologies of design and manufacture required for the 200MW class pilot generator were established. This project contributed to the progress of R & D of power apparatuses. Super-GM has started the following project (phase II), which develops the key technologies for the larger-capacity and more-compact machine, and is scheduled from 2000 to 2003. Phase II will be the first step for the commercialization of superconducting generators.
Since 1988, the development of a practical superconducting generator has been carried out in Japan. The authors have developed a rotor with a highly stabilized superconducting field winding and a stator with an air gap winding composed of double transposed copper coils. A series of tests were completed at the end of 1997. The output of 78.8MW was recorded, which was the highest value obtained worldwide. The development of the generator and the test results are described.
Some 70MW class superconducting generators have been developed in Japan to verify the basic technologies for a 200MW class superconducting pilot generator. The manufacture of a 70MW rotor with a slow response excitation had begun in 1992, and factory tests were conducted in 1996. Succeeding the factory tests, the rotor was combined to the stator with air gap windings at the verification test facility in Osaka power station, and verification tests were conducted in 1998. The advantages and reliability of superconducting generators had been clarified by these tests. In this paper, verification test results containing stability of superconducting field windings and helium cooling characteristics are described. The main results are summarized as follows: (1) The advantages of the superconducting generators, such as increasing generation efficiency and improving power system stability were verified. And the operational reliability was confirmed by the long-term operation. (2) The superconducting stability against constant current and rapid current changes corresponding to the load conditions of the 200MW class slow-response pilot generator were confirmed to be satisfactory. (3) Helium cooling characteristics such as cooling down and heat loss wore confirmed to be also satisfactory.
The development of a superconducting generator had been carried out for 12 years under the first stage of a Super GM project. The 70MW class model machine with quick response excitation was manufactured and evaluated in the project. This type of superconducting generator improves power system stability against rapid load fluctuations at the power system faults. This model machine achieved all development targets including high stability for rapid excitation control. It also connected to the actual 77kV electrical power grid as a synchronous condenser and proved advantages and high-operation reliability of the superconducting generator.
The present paper reports the development of the refrigeration system that is applied to 70MW class superconducting generators (SCG). The main subject in developing the refrigeration system for verification tests on site was to develop technology for removing impurities in helium gas, which largely affects its reliability, and to further improve the reliability and efficiency of its main components as screw compressors, turbo expanders, and a low temperature adsorber. Thus this paper deals with its planning and performance testing as well as automatic control in different modes of operation (such as cool-down, steady-state and heat run) and also the reliability analysis. It was verified that the developed refrigeration system demonstrated a higher reliability of 14, 637 hours (MTBF), larger than 10, 000 hours. The total operation time at steady state has reached 9, 320 hours with no failures in the entire testing period.
The present paper reports the development of the highly reliable refrigeration system (3 types), which is applied for 70 MW class superconducting generators (SCG). R & D of the oil-free turbo type: In the turbo type of advanced refrigeration system, a complete oil-free 80K cold compressor was developed. Moreover, the cold compressor driven by a coaxial turbine was developed to enhance the system efficiency and to save space. R & D of the oil-free screw type: In the oil-free screw rotors, taper rotors were planned to maintain a radial clearance between male and female rotors and the casing, to compensate their thermal deformation because of the heat of compression. Moreover, a seal technique was established that used a magnetic fluid and gas seals to prevent lubricating oil from bearings and the timing gear chamber into the rotor housing, under a higher rotational speed of 25, 000rpm
Super-GM and the Kansai Electric Power Co., Inc., demonstrated a field test of a 70MW class superconducting generator. The model machine, which was operated as a rotary condenser, was connected to a 77kV commercial power grid through 77/6.6kV transformers. It supplied leading 40MVar to the electric power system. The model machine showed an ability to operate stably through all the tests to the various load changes in the service electric power system. The results show that a superconducting generator has effects on voltage stabilization because of small synchronous reactance of the generator and also on the increase of leading reactive capacity compared with a conventional generator.