High-temperature Superconductor Field Winding Research Articles

A design study on 20 kW class axial flux motor with HTS field winding for 100 MPa liquid hydrogen pump

This paper presents a design study of a low-speed, high torque 20 kW class motor with a high-temperature superconductor (HTS) field coil for a liquid hydrogen centrifugal pump. The motor is designed based on three key concepts: 1) employing an axial-flux motor topology that can increase torque density by reducing the axial length together with a centrifugal pump; 2) using liquid hydrogen in a pump as a coolant for HTS coil; 3) adopting no-insulation (NI) YBCO solenoid coils as field coils of the motor to improve coil protection as well as mechanical stability. In the design process, first, an electromagnetic design of the axial type motor is obtained considering the required performance of previous commercial pumps. Considering the current and temperature margin to secure the HTS coils' stable operation, two types of HTS coils (solenoid type and triangle type) are designed and their performances are compared. Second, to evaluate validity of the electromagnetic designs, mechanical stresses in the HTS coils are estimated. By comparing the solenoid type and the triangle type, it is confirmed that the solenoid type has a distinct stress-reducing effect in terms of magnetic stress as well as rotational stress. Our design study results show the potential superior performance of the axial flux motor with HTS coils for several tens of kW applications with low speed and high torque loads such as liquid hydrogen pumps.

Compensation of NI Behaviors in Synchronous Motors With NI HTS Field Winding Using Harmonic Current Injection

Focusing on the improved operation reliability of no-insulation (NI) high-temperature superconductor (HTS) coils, various attempts are being conducted to replace conventional superconductor coils with NI HTS coils for industrial and energy conversion purposed applications. When applying NI techniques, unique behaviors of NI HTS coils due to the removal of turn-to-turn insulation should be considered with given operating conditions, because it could affect the overall characteristics of the machines. In particular, in the case of synchronous motors to which NI HTS field winding is adopted, it has been reported that periodic turn-to-turn leak currents were identified even in steady-state operation due to harmonic components, which may result in torque and loss characteristics changes. Here we report a method to offset these additional NI behaviors that may appear when NI HTS field winding is applied to synchronous motors. A brief mechanism of the proposed method was presented, and the proposed method was applied to an example model through finite element analysis. As a result, it was shown that turn-to-turn contact loss could be reduced to 2.18% without adverse effect on torque characteristics.

Characteristics comparison between air-cored and iron-cored 100 kW HTS field winding synchronous motors

This paper presents comparative research on characteristics of air-cored and iron-cored high-temperature superconductor (HTS) field winding synchronous motors. The 100 kW air-cored model is designed analytically by Spatial Harmonic Method, and based on this model, the iron-cored model having the same output power is designed for comparison. Due to the substantial difference of permeability property between air and iron-core, there is a difference of magnetic field magnitude and angle with respect to the HTS tape c-axis, resulting in a different critical current of the field winding considering the anisotropic property of HTS tape. For a detailed comparison between two models, the following key motor characteristics are calculated through the Finite Element Method (FEM) simulation: 1) critical current; 2) HTS wire length; and 3) torque characteristics. From the simulation results, it can be confirmed that the critical current value of the iron-cored model increases by 33 %. Also, in the case of the superconducting wire consumption, those of the iron-cored and air-cored models are 95.3 m and 815.6 m, respectively. So the wire usage can be reduced to about 88 % by using iron core. However, in terms of torque characteristics, the torque ripple of the iron-cored model is about twice as large as that of the air-cored model, which may be a disadvantage on vibration and acoustic noise.

A Design Study on 40 MW Synchronous Motor With No-Insulation HTS Field Winding

This paper presents a design study on a 40 MW synchronous motor having no-insulation (NI) high-temperature superconductor (HTS) field coils. An in-house analytic code was used to obtain a first-cut design based on the published parameters of the AMSC 36.5 MW ship propulsion motor as a reference. Then, design refinement was followed using the finite-element method to more accurately simulate electromechanical behaviors of the motor. After the final design was completed, transient torque responses of the NI motor, in no load and full load conditions, were simulated with our new equivalent circuit model to consider the nonlinear behaviors of the NI field coils, and compared the results with those of its insulated counterpart. The overall torque response of the NI machine was essentially identical to that of the insulated one, though a notable discrepancy was observed at the moment when the rotor acceleration started and ended. The results may imply that the NI field coils play a role as an effective damper in perspective of the torque response. The results demonstrate a potential to use the NI HTS field coils for a low-speed synchronous machine such as the ship propulsion motor.

Comparison Study on Harmonic Loss of MW-Class Wind Generators With HTS Field Winding

This paper investigates the effect of slot-pole combination on harmonic loss such as iron loss and eddy-current loss in wind generators with high-temperature superconductor field winding. In order to study the effect of stator configuration, three wind generators having the same rotor structure but different stators were purposely designed to produce 11 MW. In the analysis, 2-D time-stepped finite element analysis was used to estimate flux density waveforms, and then harmonic iron loss in the stator yoke and rotor eddy-current loss were obtained. From the simulation results, we showed that the harmonic effect on stator iron loss is not significant because magnetic loading by field winding dominates. Meanwhile, we found that the eddy-current loss in the rotor by harmonics of magneto motive force strongly depends on the slot-pole combination.

A Linear Doubly-Salient HTS Machine for Wave Energy Conversion

This paper proposes a linear doubly-salient high-temperature superconductor (HTS) machine for wave energy conversion, which is composed of a tubular stator and a tubular translator. Since the translator is a simple iron core with salient poles, it is so robust that it can be directly coupled with the reciprocating buoy. The stator consists of an iron core with salient poles, DC HTS field windings and 3-phase HTS concentrated armature windings. By using the finite element analysis, the proposed machine is quantitatively compared with its permanent magnet and copper-winding counterparts. Hence, it validates that its performance, especially the power density, can be improved greatly.

Loss Analysis of Permanent Magnet Hybrid Brushless Machines With and Without HTS Field Windings

This paper presents and implements the power loss analysis of a new kind of permanent magnet hybrid brushless (PMHB) machines with and without using high-temperature superconductor (HTS) field windings. The circuit-field-torque time-stepping finite element method together with experiential equations is developed to perform power loss analysis of the PMHB machine. Experimentation is carried out to verify the proposed loss analysis.

5 MW High Temperature Superconductor Ship Propulsion Motor Design and Test Results

American Superconductor has designed, built, tested and delivered to the U.S. Navy's Office of Naval Research (ONR) a 5MW, 230-RPM, 6-pole high temperature superconductor (HTS) ship propulsion motor. The motor uses an air core armature winding and first generation HTS wire (BSCCO-2223) field winding. The goal of the motor development project was to validate the technologies required to design and build larger HTS ship propulsion motors, as well as to develop a motor production process that streamlines development time and minimizes cost. A commercial variable frequency drive is used to power the motor. The HTS field winding is cooled with G-M coolers with gaseous helium as the cooling medium in a closed cycle. The armature is cooled by MideP. The motor was delivered to the U.S. Navy in July 2003 and met or exceeded requirements in operation (up to the facility's testing limit of 2.5MW). The motor demonstrated both full torque and full speed operation in separate tests.

Homopolar motor with high temperature superconductor field windings

A superconducting field winding, assembled with discrete coils wound with bismuth 2223 high temperature superconducting (HTS) wire, has been successfully operated in an electric homopolar motor designed and built by the Naval Surface Warfare Center. The motor's field winding is composed of two HTS coils fabricated by American Superconductor Corporation and two HTS coils fabricated by Intermagnetics General Corporation. These field winding coils were produced for the Navy under contracts with the Naval Research Center. At a HTS field winding operating temperature of 4.2 K, the motor produced 125 kW (167 hp) of output power. At a temperature of 28 K the motor power developed was 91 kW (122 hp). In comparison to other motor types, a homopolar motor provides an ideal operating environment for a superconducting magnet. The design, construction, and operating characteristics of this machine are described. Information describing the HTS field winding and its superconducting capabilities is presented along with that for the laboratory test facility used to measure the performance of the machine. Motor measured performance results and those predicted by computer simulation are compared and presented. An assessment of the state of the engineering development of HTS superconductors for magnet applications and recommendations for future development are made.

Homopolar DC motor and trapped flux brushless DC motor using high temperature superconductor materials

Two motors have been designed and built for use with high-temperature-superconductor (HTSC) materials. They are a homopolar DC motor that uses HTSC field windings and a brushless DC motor that uses bulk HTSC materials to trap flux in steel rotor poles. The HTSC field windings of the homopolar DC motor are designed to operate at 1000 A/cm/sup 2/ in a 0.010-T (100-G) field. In order to maximize torque in the homopolar DC motor, an iron magnetic circuit with small air gaps gives maximum flux for minimum Ampere turns in the field. A copper field winding version of the homopolar DC motor has been tested while waiting for 575 Ampere turn HTSC coils. The trapped flux brushless DC motor has been built and is ready to test melt textured bulk HTSC rings that are currently being prepared. The stator of the trapped flux motor will impress a magnetic field in the steel rotor poles with warm HTSC bulk rings. The rings are then cooled to 77 K to trap the flux in the rotor. The motor can then operate as a brushless DC motor.