Toshiki Hirao

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.

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.

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.

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.

Experimental results of field windings and concepts of rotor component development of superconducting generator

Superconducting field windings of superconducting generators are wound in slots which are cut on the outer surface of a support tube, and they are supported by wedges against centrifugal and electromagnetic forces. To improve reliability of field windings, AC losses due to flux change and ohmic losses due to the winding connections must be small and field windings must be tightly compressed by wedges. This paper presents experimental results of AC losses, ohmic losses, compression-displacement measurements of field windings, and design concepts of our rotor component development project.