Byeong-Soo Go

A study on the required performance of a 2G HTS wire for HTS wind power generators

YBCO or REBCO coated conductor (2G) materials are developed for their superior performance at high magnetic field and temperature. Power system applications based on high temperature superconducting (HTS) 2G wire technology are attracting attention, including large-scale wind power generators. In particular, to solve problems associated with the foundations and mechanical structure of offshore wind turbines, due to the large diameter and heavy weight of the generator, an HTS generator is suggested as one of the key technologies. Many researchers have tried to develop feasible large-scale HTS wind power generator technologies. In this paper, a study on the required performance of a 2G HTS wire for large-scale wind power generators is discussed. A 12 MW class large-scale wind turbine and an HTS generator are designed using 2G HTS wire. The total length of the 2G HTS wire for the 12 MW HTS generator is estimated, and the essential prerequisites of the 2G HTS wire based generator are described. The magnetic field distributions of a pole module are illustrated, and the mechanical stress and strain of the pole module are analysed. Finally, a reasonable price for 2G HTS wire for commercialization of the HTS generator is suggested, reflecting the results of electromagnetic and mechanical analyses of the generator.

Design of a 12-MW HTS Wind Power Generator Including a Flux Pump Exciter

A flux pump (FP) exciter injects dc current into the high-temperature superconducting (HTS) field coils of an HTS rotating machine without a slip ring and current leads. When designing a large-scale HTS generator with integrated FP exciter, the coil inductance, field current, and time constant need to be optimized for better performance of the machine. In this paper, a 12-MW HTS wind power generator with integrated FP exciter was designed. The essential parameters of a 12-MW HTS generator were optimized using the Taguchi method, targeting the minimization of weight and volume of the generator, the length of HTS wire, and the inductance. In particular, the FP exciter was adopted for supplying dc current to the HTS field coils without the power supply and the slip ring. The magnetic field distribution was analyzed using the 3-D finite-element method. The induced dc current and charging and discharging times of the FP exciter were compared with the metal current leads, for confirmation of the effectiveness of the FP exciter. The detailed results of the HTS generator design were discussed in detail.

Design and Performance Analysis of a NI-Type HTS Field Magnet for Superconducting Rotating Machines

The no-insulation-type (NI-type) high-temperature superconductor (HTS) magnet is considered a new and innovative concept for superconducting rotating machines, and it is possible to make an electrically and thermally robust magnet. The purpose of this paper is to investigate the NI-type HTS field magnet performance for superconducting rotating machines. First, specification data for a superconducting rotating machine were acquired based on electromagnetic analysis. Based on the data, the wire type, coil shape, field magnet, and armature were designed. The detailed structure of the NI-type HTS field magnet was designed using a 3-D CAD program. The performance of the NI-type HTS field magnet was tested under charge-discharge and overcurrent conditions. The NI-type HTS field magnet proposed in this paper operated well. Based on the field magnet data, an NI-type HTS field magnet-based superconducting rotating machine was fabricated. The signal condition and generating power of the fabricated HTS rotating machine were examined.

Modularization of the HTS Field Coils for a Large-Scale Superconducting Generator

In general, when a high-temperature superconducting (HTS) field coil breaks down, the overall field coils of a superconducting synchronous generator (SCSG) also stop working because the HTS field coils are connected in series. However, the modularized HTS field coil is operated individually, and thus, if the HTS field coils break down, the generator still operates even under the fault conditions. This paper deals with the modularization of the HTS field coils for a large-scale superconducting generator. The conceptual design of the modularized large-scale HTS generator was designed by using a 3-D CAD program based on electromagnetic and force analysis results. The output characteristics of the HTS generator were analyzed using a 3-D FEM program. The conceptual design of the modularized HTS field coils and fault characteristics analysis results of a 12-MW-class superconducting generator are discussed in detail.

Economic Feasibility Study of an HTS DC Induction Furnace

Conventional induction furnaces have been in operation in nonferrous metal and related industries with poor energy efficiencies of only 50-60%. Moreover, the efficiency of atmosphere furnace, one of the various heating facilities for metal billets, is about 20%. For ensuring high energy efficiency in these heating furnaces fields, as one of the better counterplans, a novel dc induction heating method using HTS magnets has been suggested. To realize the HTS dc induction furnace (HIF) in the industrial field, the most important issue is to guarantee economic favor in comparison with two different types of conventional furnaces. In this paper, we performed an economic feasibility study of an HIF in terms of electricity fee minimization. Net present value, internal rate of return, and pay-back period methods were used to evaluate the investment returns of an HIF. All indicators related to direct benefits were calculated and analyzed for finding economic feasibility. The analysis results will be applied to decision making process for the commercialization of the HIF.

Structural Design of a Module Coil for a 12-MW Class HTS Generator for Wind Turbine

Recently, high-temperature superconducting (HTS) generators are being studied to reduce the weight and size of large-scale gearless generators. However, the large-scale HTS generators have problems relating to high electromagnetic force because of their high current density and magnetic field. Therefore, the forces acting on HTS field coils should be considered as well as their support structures. This paper discusses the structural design of a module coil for a 12-MW class HTS generator for wind turbine. The 12-MW HTS generator module was designed based on electromagnetic analysis results obtained using the 3-D finite-element method. The detailed structure of the module coil was investigated considering the HTS coil bobbin, support, and cooling system. For secure design of the module coil, stress and deformation analyses were performed. Structural analysis results were compared with safety factors and critical yield stresses for each material. As the results, electromagnetic force and maximum stress of the module coil were calculated, and pole-type supports were found to be the most suitable for the 12-MW class HTS generator.

Critical Performance Analysis of HTS Magnet Wires Using an Induced Current-Based Measurement System

Studies on wide and stacked high-temperature superconducting (HTS) wires aim to increase the critical current of the wires. This paper describes the design and fabrication of an induced current-based performance measurement system and a critical performance analysis of HTS magnet wires using this system. In the experiment, the induced current, critical current, and joint resistance of stacked HTS wires under charge and discharge conditions were investigated. The results obtained were compared with those achieved using the four-terminal method, which is the conventional measurement method. The measurement system and the results of the critical performance analysis of the HTS wire are discussed in detail.

Optimal Design of a MW Class SCSG for a Tidal Current Power Generation System

A superconducting synchronous generator (SCSG) can be expected to decrease the size and weight compared to conventional tidal current generators. This paper proposes an optimal design of a 2 MW class SCSG for a tidal current power generation system. The proposed optimal design of the SCSG will reduce the length of the high-temperature superconducting wire as well as the weight and volume of the SCSG. The 3D finite element method is used to analyze the magnetic field distribution. The optimized 2 MW SCSG is compared with a 2 MW conventional generator. As the optimized SCSG is more compact and lighter than a conventional generator, it will be efficiently applied to practical tidal power systems.

Induced Current-Based Performance Measurement System for Wide and Stacked HTS Wires

Recently, high-temperature superconductor (HTS)-based devices have been applied to practical electric power systems. In order to increase the critical currents of HTS wires, wide and stacked HTS wires are being extensively researched. However, general systems for testing critical currents via voltage taps are not accurate for measuring the critical currents of wide and stacked HTS wires. This paper proposes an induced current-based performance measurement system for wide and stacked HTS wires. The system consists of wide and stacked HTS wires and induction coils made of 2G HTS wire. The electromagnetic performance of the HTS wires and induction coil is analyzed using a finite element method program. The basic structure of the performance measurement system is designed and fabricated based on the electromagnetic analysis results. In the experiment, the characteristics of the HTS wire are analyzed under charge and discharge conditions from the viewpoint of induced currents. The current of the stacked HTS wires is measured by a Rogowski coil. As a result, we can accurately identify the characteristics of the wide and stacked HTS wires, such as critical current and joint resistance.