H.M. Kim

Numerical Analysis and Design of Damper Layer for MW-Class HTS Synchronous Wind Turbine Generator

This paper presents a numerical analysis on MW-class high-temperature superconducting (HTS) synchronous generator, especially focusing on damper layer design. Our research program to develop a large-scale HTS wind turbine generator (WTG) core technology, a two-dimensional electromagnetic FEM model of the direct-drive HTS WTG, comprised of 24 air-core type HTS race track coils (24 poles), has been built. The damper is used for stable operation of HTS field coil against varying magnetic field by change of rotation speed. This model is designed to obtain basic operating parameters for HTS WTG, including magnetic field distribution and induced electromotive force, in static and transient condition. First, the parameters in static condition, which means that the rotating speed is constant, are compared with our design parameters to confirm the feasibility of our numerical analysis. Second, in transient condition, we focused on the reaction between rotating magnetic field and its stator components, damper, and armature winding. By changing damper material having different electrical conductivity and magnetic permeability, we concluded our damper design to be applicable to our MW-class HTS synchronous generator model.

Analysis of the operational characteristics of a heater-trigger type high-T/sub c/ superconducting power supply

This paper deals with the design and fabrication of a heater-trigger type high-T/sub c/ superconducting (HTSC) power supply, and its characteristics has been analyzed through experiments. A heater-trigger HTSC power supply consists of two heaters, an electromagnet, and a YBCO superconducting bulk. In this experiment, a 0.6-T magnet and a 2.3-A dc heater current were used and 190 s and 380 s were used for the pumping period. In order to measure the pumping current with respect to the magnet flux changes, hall sensors were installed at the surface of the YBCO bulk and inside of an iron core. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping current has reached about 12 A. In computer simulation, the maximum pumping current of the system has been predicted to be about 13 A.

Performance Analysis of a Superconducting Motor for Higher Efficiency Design

The superconducting motor shows several advantages such as smaller size and higher efficiency against conventional motor especially utilized in ship propulsion application. However, this size reduction merit appears in large capacity more than several MW. We are going to develop a 17-MW class synchronous motor with a rotating HTS (high-temperature superconducting) coil that is aimed to be utilized for ship propulsion, therefore it has a slow rotating speed of about 200 rpm. The ship propulsion motor must generate high electromagnetic torque instead of low-speed. Therefore, the rotor (field) coils have to generate large magnetic flux that results in large amounts of expensive HTS conductor for the field coil. In this paper, a 17-MW HTS motor for ship propulsion is designed with smaller manufacturing cost by HTS field coil length reduction because the HTS conductor cost is a critical factor in the construction cost of an HTS motor. Furthermore, the output performance of the machine is simulated based on the equivalent circuit model of the synchronous motor with back electromagnetic field values from three-dimensional magnetic field calculation. The simulation results are used to design higher efficiency motor.

Analysis of a High-Tc Superconducting Power Converting System

This paper presents the analysis of a high-Tc superconducting (HTS) power converting system, as well as its operational characteristics. The converting system can be used to charge and discharge a magnet made of series-connected pancake coils. The HTS converting system consists of two heaters, a primary copper winding, a secondary HTS winding, a series-connected HTS pancake coil, an iron core and a conventional copper load. In the experiments, the charging and discharging periods were 7.5 and 2 s, respectively. A partial region of the superconducting tape in a secondary HTS winding is switched to a normal region by a buried heating coil. To measure the converting-current with respect to the magnet flux changes, a hall sensor was installed at the center of the pancake coil. In this experiment, the charging-current and discharging-energy reached about 51.7 A and 36.8 J, respectively. The experimental results have been compared with theoretical predictions by using the finite difference method.

Design, fabrication and testing of a heater-trigged high-Tc superconducting power supply

This paper deals with the design and fabrication of a heater-trigged high-Tc superconducting (HTS) power supply. Its characteristics have been analyzed through experiments. A heater-trigged HTS power supply consists of two heaters, an electromagnet, and a YBCO bulk superconductor. The timing sequential control of two heaters and an electromagnet is an important factor to generate pumping-current in the bulk YBCO superconductor. The thermal analysis of switching parts of the YBCO superconductor according to the heater input was carried out. Based upon the analysis, the 0.6 T electromagnet and the 2.3 A dc heater current were optimally derived, and 190 sec and 380 sec for the pumping period were selected in this experiment. In the experiment, the maximum pumping current reached about 12 A.