Susumu Maeda

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.

Research and development of slow response type 70 MW class superconducting generator with high-current density superconductors

Abstract Some 70 MW class superconducting generators have been developed in Japan to verify the basic technologies for a 200 MW class superconducting pilot generator. The manufacture of a 70 MW rotor with a slow response excitation began from 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 including 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 variations corresponding to the load conditions of the 200 MW class slow response pilot generator were confirmed to be satisfactory and (3) helium cooling characteristics such as cooling down and heat loss were confirmed to be also satisfactory.

Design Concepts and Experimental Results of Superconductor for Field Windings of 70mw Class Superconducting Generator

AC losses and critical currents of three types of superconductors were measured to evaluate the characteristics of the superconductors which are designed to meet the requirements for the field windings of a 70MW class superconducting generator with low response excitation system. The superconductors used for the test are compacted stranded cables composed of Cu-CuNi-NbTi strands, and have the same cable size. The cross sectional structure of the strands and matrix ratios for tested cables are different. This paper presents the results of the experiment and design concepts of the superconductor for the 70MW class generator.

Temperature dependence of insulation resistance and current components for generator stator bars

Insulation resistance measurement is one of the widely used methods to diagnose insulation conditions of turbine generators. Since insulation resistance tends to decrease with the increasing temperature, it needs to be evaluated on exactly the same basis. Insulation resistance of the epoxy-mica based insulation system does have temperature dependence in the temperature range over 40°C, but the insulation resistance is nearly constant in the temperature range under 40°C. In order to study the mechanism of the temperature dependence, current components such as conduction current IG, surface leakage current IL and polarization current IP were measured by applying a DC high voltage across the main insulation under the temperature range of 10°C to 80°C and the time range of 0 to 30 min. The dominant current component of 1 minute value is IP, and it is nearly-constant less than 40°C and tends to increase over 40°C. Therefore the temperature dependence of the insulation resistance is determined by that of IP. Since the insulation resistance is nearly-constant under 40°C, no temperature correction is required as long as it is measured under 40°C.

Acoustic emission monitoring on a model field winding for the 70 MW class superconducting generator

Abstract Acoustic emission monitoring on a model field winding for the 70 MW class superconducting generator was performed during cooldown, excitation and quenches to diagnose the integrity of the model field winding and improve the reliability of the field windings for the generator. The results confirm that the acoustic emission signals are mainly due to conductor motions which cause premature quenching of the winding. It is therefore important to support the field windings as rigidly as possible to prevent conductor motions and to increase the stability of the field windings.