High-temperature Superconducting Field Coils Research Articles

Feasibility Study of the Impregnation of a No-Insulation HTS Coil Using an Electrically Conductive Epoxy

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1] , [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines.

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.

Design and Experiment of an HTS Flux-Switching Machine With Stationary Seal

This paper proposes and develops a new kind of cryogenic cooling system for high-temperature superconducting (HTS) flux-switching (FS) machine using stationary seal for its cooling Dewar. Test results show that this cryogenic cooling system can offer the cryogenic operating environment around 63 k for the racetrack-shaped HTS field coils. Based on the proposed cryogenic cooling system, a new HTS-FS machine with segmented rotor is proposed. By using the finite element analysis, the machine performance is analyzed accordingly. Hence, the electromagnetic characteristics of the proposed machine are verified.

Operational Characteristics of HTS Coils With Flux Diverters in Semipersistent Mode Under Alternating Magnetic Field

This paper deals with the effect of magnetic flux diverters on the current decay behaviors of high-temperature superconducting (HTS) coils which operate in semipersistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machines, the HTS field coil can be designed to operate in PCM to obtain a steady magnetic field during operation. Due to the alternating magnetic field from the armature winding, the HTS field winding experiences an external magnetic field. As a result, the additional magnetization ac loss in the field coil would be induced, and it affects the current decay characteristics. In order to improve the current decay behavior of the HTS field coil, the use of flux diverter made of magnetic material can be considered. In this paper, we experimentally investigated the current decay characteristics of HTS field coils with magnetic flux diverters under alternating magnetic field. The measurement setup, which is composed of HTS field coil and armature coil, was fabricated. The measurement test of the current decay on the HTS field coil in PCM operation was carried out as functions of the amplitude and frequency of the armature coil.

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.

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.

Determining the Operating Current of No-Insulation Field Coils in HTS Generators

This paper proposes a new method for calculating the operating current of high-temperature superconducting (HTS) no-insulation coils whose overcurrent characteristics are more stable than those of conventional field magnets in superconducting generators. Problems related to calculating the operating current of conventional high-temperature superconductors have been analyzed, and the conditions for coils to overcome such problems have been proposed. To complement electrical stability issues of conventional HTS field coils, a small pancake coil was constructed from the Bismuth strontium calcium copper oxide (BSCCO) first-generation HTS wire with noinsulation winding. The pancake coil was then tested. The tests confirmed that the no-insulation coil was electrically stable. In addition, it was confirmed that quenching did not occur in electrically stabilized coils, even at higher input currents than the critical current value of the coil. In addition, the magnetic field value having the largest effect on the decrease in the critical magnetic field in the superconducting coil was calculated through finite-element method analysis, thus predicting the effective current of the superconducting coil. This analysis was compared with experimental results to demonstrate the validity of the proposed method.

Electromagnetic Design of a 15 MW-Class HTS Flux Switching Synchronous Generator considering Mechanical Stress of the Rotor Core

This paper introduces a novel flux switching synchronous generator (FSSG) using high-temperature superconducting (HTS) field coils. Unlike conventional superconducting synchronous generators, the HTS field coils in the proposed FSSG are mounted in the stator and do not rotate during operation. Therefore, the design and fabrication of the cooling and excitation systems for HTS field coils are easier than those for the conventional superconducting synchronous generator. To verify the feasibility of the structure, a 15 MW-class FSSG was designed using a fundamental design methodology considering the mechanical stress of the rotor core. The design methodology uses mechanical and electromagnetic equations. It defines the size of the rotor first using mechanical equations for the rotor and designs the HTS field winding and armature winding using the electromagnetic equations and an FEM analysis. In addition, the operational characteristics of the FSSG were analyzed by a transient motion analysis using the FEM program. This paper could be utilized to develop superconducting synchronous generators.

Parameter Design by a Novel Method and Optimization of the Field Coil for a 500 kW Air-Gap HTS Generator

Due to the special structures of high temperature superconducting (HTS) generators, the traditional magnetic circuit method for electromagnetic designing is not yet appropriate. In this paper, the separated variables method is introduced to calculate the magnetic fields of an HTS generator, and by this novel method, parameters of a 500 kW HTS generator is designed. Furthermore, the variations of harmonics content and amplitude of flux density in the air gap with the different open angles of HTS field coil are evaluated. Results obtained by the analytical method are basically in agreement with that obtained by finite element method. It is shown that the analytical method is effective and convenient in the design of HTS generator.

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.

Comparison of superconducting generator with 2G HTS and MgB2wires

This paper compares the features of second generation (2G) High Temperature Superconducting (HTS) field coil with those of magnesium diboride (MgB2) field coil for a 10 MW class superconducting generator. Both coils can function effectively in their respective magnetic flux density range: 10-12 T for 2G HTS field coil, 2 T for MgB2 superconducting field coil. Even though some leading researchers have been developing 10 MW class superconducting generator with 2G HTS field coil, other research groups have begun to focus on MgB2 wire, which is more economical and suitable for mass production. However 2G HTS wire is still appealing in functions such as in-field property and critical temperature, it shows higher in-field property and critical temperature than MgB2 wire.

Experimental study of the effects of alternating fields on HTS coils according to the winding insulation conditions

This paper examines the effects of alternating fields on high-temperature superconducting (HTS) coils according to the winding insulation condition. Alternating fields can occur in synchronous machines (armature reaction, faults) and other devices. In superconducting synchronous machines, alternating fields affect the operational characteristics of the machine and the superconducting field coil. Therefore, a method of reducing the effects of alternating fields is necessary in superconducting synchronous design. In this study, the effects of alternating fields on the HTS field coil according to the winding insulation condition were experimentally evaluated. The experimental results show that HTS coils made using the no-insulation technique can be a solution for reducing the effects of the alternating field. These results are expected to suggest useful data for applications of HTS field coils in superconducting synchronous machines.

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.

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.

Conceptual Design of a Field Coil for 5 MW HTS Synchronous Machine

Compared with a conventional rotating machine, a superconducting rotating machine fabricated by High Temperature Superconducting (HTS) tape has superior performance and efficiency due to the HTS field coil for the rotor which can generate high magnetic flux intensity. The two primary factors for the design of the HTS rotational machine are how to construct the optimal magnetic field path through the air gap located between the rotor and the stator and how to enhance the linkage magnetic flux density between the armature coil in the stator and the field coil in the rotor. A 5 MW HTS motor for ship propulsion is planned for development in early 2011 by a Korean collaboration group of KERI and DOOSAN Heavy Industry. As a part of this R&D efforts, we designed and analyzed the field coil for a 5 MW HTS synchronous motor. In this paper, the computational results of the magnetic field distribution on the whole winding regions of the HTS field coil of the superconducting rotating machine will be also presented and discussed.

大出力超伝導回転機器に向けたキーハードの開発

This project aims to establish key hard technologies for large-scale high-temperature superconducting (HTS) rotating machines for a ship propulsion system. Using HTS technology, compact, right weighted and highly efficient ship propulsion motors can be realized. The objectives of the project are R&D of robust and reliable HTS field coils with low loss,and compact cooling systems integrated to a rotor and design technology for a 20 MW-class ship propulsion motor. This project is now in the first year of the stage III; stage II was completed in the last Japanese fiscal year. This report reviews the R&D results in stage II and the plans in stage III.

Electrical performance analysis of HTS synchronous motor based on 3D FEM

A 1-MW class superconducting motor with High-Temperature Superconducting (HTS) field coil is analyzed and tested. This machine is a prototype to make sure applicability aimed at generator and industrial motor applications such as blowers, pumps and compressors installed in large plants. This machine has the HTS field coil made of Bi-2223 HTS wire and the conventional copper armature (stator) coils cooled by water.The 1-MW class HTS motor is analyzed by 3D electromagnetic Finite Element Method (FEM) to get magnetic field distribution, self and mutual inductance, and so forth. Especially excitation voltage (Back EMF) is estimated by using the mutual inductance between armature and field coils and compared with experimental result. Open and short circuit tests were conducted in generator mode while a 1.1-MW rated induction machine was rotating the HTS machine. Electrical parameters such as mutual inductance and synchronous inductance are deduced from these tests and also compared with the analysis results from FEM.

Electrical parameter evaluation of a 1 MW HTS motor via analysis and experiments

A 1MW class HTS (high-temperature superconducting) synchronous motor has been developed. Design concerns of the developed motor are focused on smaller machine size and higher efficiency than conventional motors or generators with the same rating simultaneously reducing expensive Bi-2223 HTS wire which is used for superconducting field coil carrying the operating current around 30K (−243°C). Influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power during motor and generator operation. The developed motor was also analyzed by three-dimensional electromagnetic FEM (finite element method) to get magnetic field distribution, inductance, electromagnetic stress and so forth.This motor is aimed to be utilized for industrial application such as large motors operating in large plants. The HTS field coil of the developed motor is cooled by way of Neon thermosiphon mechanism and the stator (armature) coil is cooled by water through hollow copper conductor. This paper also describes evaluation of some electrical parameters from performance test results which were obtained at steady state in generator and motor mode of our HTS machine.

Performance test of a 1 MW class HTS synchronous motor for industrial application

This paper deals with development activities of high temperature superconducting (HTS) synchronous motor at DOOSAN heavy industry and Korea Electrotechnology Research Institute (KERI) in Korea, and is sponsored by DAPAS program which is supported by Korean government. The final aim of the project is realization of HTS motor in the field of industry such as large driving pumps, fans and compressors for utility and industrial environments. At present time, 1 MW HTS motor is developed for the purpose to fully represent the design and manufacturing issues for the larger capacity machine. The number of pole and rotating speed of machine are 2 pole and 3600 rpm. The HTS field coil of the developed motor is cooled by way of neon thermosyphon mechanism and the stator coil is cooled by water through hollow copper conductor. This paper describes status of 1 MW HTS motor development, such as design, fabrication and performance test results, which was conducted at steady state in generator mode and motor mode.

Performance of High Temperature Superconducting Field Coils for a 100 HP Motor

A superconducting motor consisting of high temperature superconducting (HTS) rotor and air-core stator is under development in Korea Electrotechnology Research Institute. HTS motor was designed for having the rated power of 100 HP at 1800 rpm. HTS field winding is composed of sixteen HTS race track shaped coils wound with stainless steel-reinforced Bi-2223 tape conductor by react and wind fabrication method. Nomex paper was used for electrical insulation. Each of four field coil assemblies was constructed with four double pancake sub-coils, mechanically stacked and electrically connected in series. Four field coil assemblies were fixed on an aluminum support structure to make effective heat transfer. Voltage terminals were attached to both ends of joints to measure joint resistances. HTS field winding was tested at 77 K, and the Joule heats generated at all the joints was calculated. In this paper, design, construction and testing of HTS field winding, Joule heat generated by the joints, and operating current were discussed.