Kwangmin Kim

Practical Design of a 10 MW Superconducting Wind Power Generator Considering Weight Issue

Recently, gearless type generators, which have very low rotation speed and high torque, have been preferred over the geared type due to the problem of the gearbox reliability. In particular, a high-temperature superconducting generator is promising for wind power applications because of its advantages of weight, size, and efficiency. In this paper, a 10-MW class superconducting wind power generator is designed using Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O wires, and the weight of the superconducting generator is estimated. The finite elements method is used to analyze the magnetic field distribution, and the 3-D CAD program is used to calculate the weight of the super-conducting synchronous generator. The designed 10-MW class superconducting generator is analyzed and discussed considering the proper weight. The designed 10-MW superconducting generator will be effectively utilized in the construction of the 10-MW class wind power generation system.

Operating Characteristics of an Insulationless HTS Magnet Under the Conduction Cooling Condition

This paper considers the insulationless high-temperature superconducting (HTS) magnet as a new and innovative concept for dc applications due to its benefits as compared to conventional HTS magnets with insulation layers between HTS conductors. The purpose of this paper is to study the operating characteristics of an insulationless HTS magnet. The normal operating characteristics of the insulationless HTS magnet were investigated according to the various current levels. Thermal stability of the insulationless HTS magnet was also analyzed. The critical current of the insulationless HTS magnet was measured at 40 K. The temperature distribution of the insulationless HTS magnet was measured using thermocouples. The experiment results demonstrate superior thermal stability characteristics in the insulationless HTS magnet. Thus, it is confirmed that the thermal performance of large-scale HTS magnets can be enhanced by applying insulationless magnets instead of general insulated HTS magnets.

Development of a brushless HTS exciter for a 10 kW HTS synchronous generator

HTS synchronous generators, in which the rotor coils are wound from high-T c superconducting wire, are exciting attention due to their potential to deliver very high torque and power densities. However, injection of the large DC currents required by the HTS rotor coils presents a technical challenge. In this paper we discuss the development of a brushless HTS exciter which operates across the cryostat wall to inject a superconducting DC current into the rotor coil circuit. This approach fundamentally alters the thermal load upon the cryogenic system by removing the need for thermally inefficient normal-conducting current leads. We report results from an experimental laboratory device and show that it operates as a constant voltage source with an effective internal resistance. We then discuss the design of a prototype HTS-PM exciter based on our experimental device, and describe its integration with a demonstration HTS generator. This 200 RPM, 10 kW synchronous generator comprises eight double pancake HTS rotor coils which are operated at 30 K, and are energised to 1.5 T field through the injection of 85 A per pole. We show how this excitation can be achieved using an HTS-PM exciter consisting of 12 stator poles of 12 mm YBCO coated-conductor wire and an external permanent magnet rotor. We demonstrate that such an exciter can excite the rotor windings of this generator without forming a thermal-bridge across the cryostat wall. Finally, we provide estimates of the thermal load imposed by our prototype HTS-PM exciter on the rotor cryostat. We show that duty cycle operation of the device ensures that this heat load can be minimised, and that it is substantially lower than that of equivalently-rated conventional current leads.

Performance Analysis of a Toroid-Type HTS SMES Adopted for Frequency Stabilization

Superconducting magnetic energy storage (SMES) can overcome fluctuations in frequency because of its fast response time in charging and discharging energy. To stabilize the fluctuations in frequency of wind power generation systems (WPGSs), HTS SMES systems should be connected to the terminal of the WPGSs. Ulleung Islands power network in Korea was modeled with a real-time digital simulator (RTDS) to demonstrate the effectiveness of SMES at stabilizing frequency. A toroid-type HTS SMES cooled by conduction cooling and a DC/DC chopper to charge and discharge current were fabricated for the experiment. The simulation results show the frequency stabilization effected by the HTS SMES system with its operational characteristics such as real time variation in current and temperature.

EMTDC Based Simulation of 10 MW Class Grid-Connected Superconducting Wind Turbine Generator

It is believed that the size of wind turbines on offshore wind farms can be increased up to 10 MW. A superconducting synchronous generator (SCSG) is advantageous to a large-scale wind turbine because of its weight and volume. In this paper, a grid-connected large-scale superconducting wind turbine generator is analysed under varying wind speeds. A 10 MW SCSG is designed by the finite elements method (FEM). The parameters of the designed SCSG are calculated and applied to a modeled SCSG in a Power System Computer Aided Design/Electromagnetic Transients including DC. The electric and dynamic performances of superconducting wind turbine generators are analysed in this simulation. This paper shows the effectiveness of the grid-connected superconducting wind turbine generator for offshore applications.

Design and Manufacturing of a SMES Model Coil for Real Time Digital Simulator Based Power Quality Enhancement Simulation

The Superconducting Magnetic Energy Storage (SMES) system is a key technology for overcoming the voltage sag, swell, interruption, and frequency fluctuation with the fast response speed of current charge and discharge. A toroidal-type SMES is designed using a 3D CAD program, and the inductance and AC loss characteristic during operation are analysed using Finite Element Method (FEM) program. The toroidal-type magnet consists of 30 double pancake coils (DPC). The single pancake coils (SPC), constituting the double pancake coils, are arranged at an angle of 6° from each other, based on the central axis of the toroidal-type magnet. The conduction cooling method is used for the toroidal-type SMES cooling. To evaluate the characteristics of the over-mega-joule class grid-connected HTS SMES system, the authors implemented a simulation by which the SMES coil could be connected to the Real Time Digital Simulator (RTDS). Using the simulation, users can perform voltage sag and frequency stabilization simulations with a real SMES coil in real time and easily change the capacity of the SMES system as much as they need. The effectiveness of the toroidal-type HTS SMES system is demonstrated through the RTDS-based simulation and the results are briefly discussed.

Design and Performance Evaluation of a Multi-Purpose HTS DC Induction Heating Machine for Industrial Applications

In general, conventional induction heating system is designed only for a specific metal billet or object, because the heating system should be specialized to guarantee the best performance regarding heating quality and efficiency. It has been applied to large heating systems in metallic processing industries. A DC induction heating method using HTS magnets can be one of the better counterplans for higher efficiency and multi-purpose heating system. In this paper, we evaluated a performance of a 10 kW-class multi-purpose HTS DC induction heating machine without additional function or equipment, and performed efficiency analysis on various metals, including aluminum, copper, and iron billets. In addition, heating characteristics of other materials were simulated and analyzed through finite elements method (F.E.M.) models. The results demonstrate that the 2G HTS DC induction heating machine is applicable for all the ferrous and nonferrous metals and useful for large scale industrial applications.

Stress Analysis for Toroid-Type HTS SMES Coil and Bobbin Structure Considering Large Parallel Magnetic Field

A 2.5 MJ HTS superconducting magnetic energy storage (SMES) system is under development to compensate the sag or instantaneous black out for a utility side. The toroidal-type structure is adapted to reduce the perpendicular magnetic field and the stray field at outside of SMES. A toroidal-type magnet shows a small perpendicular magnetic field. However, parallel magnetic field is much larger than perpendicular one. Therefore, Lorentz force of HTS tape can be so strong and the stress analysis should be carried out to verify that the maximum hoop stress and normal stress are in appropriate range. In addition, overall inward force of an HTS pancake winding in toroidal-type magnet is very strong and stress analysis for the bobbin and its supporting parts is important for a design a mechanically stable structure. This paper describes an analysis and design result for a toroidal-type HTS SMES magnet considering orthotropic material properties, large magnetic field and the resulting Lorentz force.

Stator Winding Fault Influence on the Field Coil of a 10 MW Superconducting Synchronous Generator

It is important to analyze the transient characteristics of large synchronous generators according to the trend of the extension of wind turbines. The fabricated field coil of a synchronous generator using high-temperature superconducting (HTS) wire is somewhat influenced by the external magnetic field of the stator in a real environment. This paper describes the electromagnetic analysis of an HTS field coil of a 10-MW superconducting synchronous generator during stator winding faults. The real-time digital simulator is used to simulate a fault condition of the 10-MW SCSG. Also, the finite-element method is used in each operating condition, including normal and transient conditions, to analyze the influence of the HTS field coil. Based on the simulation results discussed here, there do not appear to be any significant problems regarding the electromagnetic operation of the HTS field coil during transient conditions of the stator. This paper will be used in the analysis of the transient characteristics of a large superconducting synchronous generator during stator winding faults.

Design and Mechanical Stress Analysis of a Toroidal-Type SMES Magnet

This paper investigates the mechanical stresses of a toroidal-type superconducting magnet (TSM). The TSM is designed by 3D CAD program. The Bi-2223 high temperature superconducting (HTS) wire made by soldering brass on both sides of the superconductor is used for the magnet winding. The TSM consists of 30 double pancake coils (DPC). Single pancake coils (SPC) constituting the double pancake coils are arranged at an angle of 6 from each other based on the central axis of the TSM. The mechanical stresses due to the Lorentz force caused by the operating current are analyzed using FEM. These fundamental data will effectively be applied to design a toroidal-type superconducting magnetic energy storage.