Ship Propulsion Motor Research Articles

A Design Study on HTS Halbach Array for Field Coil of 40 MW Ship Propulsion Motor

A 40 MW ship propulsion motor was designed with a high temperature superconductor coil Halbach array. The Halbach array was applied to the field coil of the motor for further performance improvement. We performed our design study on two different motor types: Halbach array inner positioned field coil motor (HIFM) and Halbach array outer positioned field coil motor (HOFM). The design for the field coil was optimized with NSGA-II. Final models were selected for HIFM and HOFM, respectively, and to estimate the effect of the HTS coil Halbach array, they were compared with reference motors with a conventional field coil. Both HIFM and HOFM showed a 7% increase in the flux to the air-gap. As the shielding effect of the Halbach array in HOFM reduced by 70% the weight of the iron shield, HOFM showed comparable weight compared to the conventional inner field coil motor. This overcomes the problem of the low power density of the outer field coil motor. With the Halbach array field coil, a design topology having the stationary field coil on the outer side of the motor would be realized with a simplified cooling structure while maintaining the light shield weight.

Current Status and Future Prospects of High-Temperature Superconducting Rotating Machine Technology for Ships -Ship Propulsion Motor to Marine Current Generator-

Current Status and Future Prospects of High-Temperature Superconducting Rotating Machine Technology for Ships -Ship Propulsion Motor to Marine Current Generator-

Design and test results of a novel quench protection circuit for a HTS ship propulsion motor

This paper describes a novel configuration of a quench protection circuit for a high-temperature superconducting (HTS) ship propulsion motor that can protect the HTS coils from an unexpected outage in its cryogenic cooling system. The quench protection circuit consists of conductor parts placed adjacent to the HTS coils and dump resistors and diodes placed in the cryogenic-temperature and normal-temperature areas, respectively. The conductor parts are shaped and arranged such that the magnetic coupling with the HTS coil is extremely large. Thereby, the current of the HTS coils can be instantaneously attenuated immediately after the quench protection is activated. With this configuration, the electromagnetic energy of the HTS coils can be absorbed in the dispersed parts. This can make the dump resistors smaller and make it easier to install them on a HTS ship propulsion motor. By analysing the equivalent electric circuit model of the protection circuit, we derived the conditions under which instantaneous current attenuation of the HTS coil occurs. In accordance with the conditions, we have fabricated a quench protection circuit that protects one HTS field pole of the 3 MW HTS motor developed by Kawasaki Heavy Industries. The fabricated circuit was empirically evaluated and proved to be highly effective in quench protection. The present quench protection circuit technology contributes to the practical application of HTS ship propulsion motors.

Development of RE-Ba-Cu-O Bulk Superconductors, QMG

This paper describes the development of RE-Ba-Cu-O (RE:Y or rare earth elements) bulk superconductors (“bulks”). HTS bulks have a great potential to pioneer a new application field of superconductors. The high-quality HTS bulks developed by Nippon Steel Corporation are called “QMG”, which is a single-grained material of REBa2Cu3Ox (RE123) with RE2BaCuO5 (RE211) inclusions finely dispersed in the superconducting matrix. The name QMG originally comes from the initial process, “Quench and Melt-Growth”. However, no quench step is required in the advanced QMG process, and thus “Q” now means “Quality” instead of “Quench”. The key point of QMG technologies is the simultaneous control of the crystal growth and the micro-structure. Although it is believed to be very difficult to produce large single-grained HTS bulks exceeding 80 mm in diameter, we have succeeded in enlarging QMG up to 150 mm using the RE compositional gradient method. These ultra-large HTS bulks have been used for the superconducting magnetic bearing (SMB) of the flywheel energy storage system in Yamanashi, Japan, contributing to non-contact support of a heavy 4,000 kg rotating flywheel. In addition to SMB, other promising application are HTS bulk magnets for ship propulsion motors, wind or tidal power generators, and desktop cryogen-free NMR/MRI. HTS bulks are also an ideal material for current leads. Different bulk properties are required for different applications. We have therefore customized QMG bulks depending on application requirements: Dy-QMG for current leads, Eu-QMG for NMR/MRI, and Gd-QMG for other HTS bulk applications.

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.

Study of neon heat flux in thermosyphon cooling system for high-temperature superconducting machinery

High-temperature superconductors (HTS) applied to rotating machine draw much interest in the shipbuilding industry as the urge to get high-power density and efficient electric propulsion systems. To achieve an optimal performance of HTS field pole magnets in ship propulsion motors, it is crucial to regulate the operating temperature under 40 K and a simple and reliable cooling system is necessary. A thermosyphon (TS) is highly suitable since its operation principle consists in using natural convection without the intervention of mechanical circulation pump. The system composition is simple and light-weight. The TS benefits from a high heat transfer coefficient thanks to latent heat. The available temperature for TS depends on the saturation temperature of the refrigerant, which provides adequate controllable cooling for cryogenic machine application. A TS system using neon enables us to supply cooling temperatures of 28–40 K range. To determine the optimal gas-liquid state operation for HTS motors, a scaled model of a 20 MW motor TS cooling system was designed and constructed. This enabled us to visualize any phenomena and transient state change inside the evaporator part of the rotor. We studied heat transfer capacity under heat load for different neon quantities. Neon heat flux was then calculated to determine the heat transfer area for effective cooling. The boiling curve leads to the refined evaporator design with optimal heat transfer area. Introducing coaxial tubing between condenser and evaporator, possible sustainable liquid-gas circulation has been achieved without interruption under inclined condition required for ship operation. The present results contribute to the next stage HTS ship propulsion motor and superconducting machine design.

Study of the heat transfer capacity of thermosyphon cooling system under the inclined condition

Machine applications with superconductors attract much interest in the industry. It is crucial to maintaining the operating temperature range between 28 K and 40 K for high-temperature superconductor (HTS) field poles. A thermosyphon (TS) is a suitable choice for HTS applications’ cooling system. The cryo-mechanical system composition is simple, lightweight and based on natural convection therefore not using any mechanical pump. Considering the rotating application, an adiabatic tube is necessary to carry the cryogen from the vertical condenser portion toward the horizontal evaporator part. However, this tube shape prevents the natural convection when in an inclined configuration which can occur for applications such as ship propulsion and electrical aircraft motors or generators. In this work, we focused on and investigated the heat transfer capacity of TS for inclinations. The results show that the TS cooling system employing the coaxial tubes architecture maintained the natural convection even under inclined conditions

Loss Analysis of a 3-MW High-Temperature Superconducting Ship Propulsion Motor

We developed a 3-MW high-temperature superconducting (HTS) motor for ship propulsion and demonstrated high efficiency, high-output density, and reliability above a certain level. To further promote the commercialization of the HTS motor, it is necessary to enhance its design technology to better satisfy the requirements for ship propulsion. To accomplish this, we need to improve the loss prediction method, as this is essential in the design of a high-efficiency motor. Since there are complicated losses in the 3-MW HTS motor, it is more difficult to deduce the detailed composition within the overall losses of the HTS motor than it is with conventional motors. This paper describes a loss analysis of the 3-MW HTS motor that is used to improve the loss prediction method. The loss at 3 MW operation was broken down in detail using the data obtained from a performance test, an open-circuit test, a short-circuit test, a nonrotating test, and an electromagnetic analysis result. The loss analysis results showed that the Joule heating loss on the armature, the individual wire eddy current loss on the armature, and the rotor cooling loss were comparatively large. The presently obtained results would form a basis for the next stage development study of reducing loss.

Development of a MW-Class 2G HTS Ship Propulsion Motor

This paper describes the design and fabrication progress of a MW-class 2G high-temperature superconductor (HTS) motor for the ship propulsion application at Doosan Heavy Industries and Construction. The most important component of an HTS motor is the rotor, which is composed of HTS coil, torque disk, damper, and hollow shaft. The HTS rotor using hastelloy-based 2G HTS coils was designed and built. Open-circuit and short-circuit characteristics of the superconducting motor were investigated and compared with the analysis results at reduced excitation to verify the design. Preliminary testing of a 2G HTS motor has been conducted at a few hundred kW as per the design. Through these results, we verified that most of the design criteria could be satisfied.

Study of HTS Machine System Cooling With a Closed-Loop Thermosyphon: Stability of Unsteady Heat Load and Transient Conduction

Thermosyphoning (TS) is a heat exchange mechanism that uses a circulating refrigerant based on natural convection with no need for a mechanical pump. This cooling technique has been employed to circulate liquid coolant and gaseous coolant for high-temperature superconductor (HTS) rotating machine systems. These machines operate with an HTS field pole in the temperature range from 25 to 40 K, which are suitable temperatures for the survivability of HTS wires. The cryomechanical components are simple; there are a condenser, an evaporator, and adiabatic tubes located between the condenser and the evaporator. For applications to ship propulsion motors or generators of the radial gap type, the liquid/gas coolant flow along the adiabatic tube inside the rotating shaft may be considerably affected by the ship's rolling and/or pitching motion. In this work, we studied the temperature stability and heat load survivability of cryogenic TS, by constructing a 100 W @ 30 K-grade model. We investigated the temperature, thermal resistance, and heat flux, with a maximum load up to 60 W, of ground and onboard tests. The observed TS behavior indicates that there is sufficient survivability to assemble megawatt-class ship propulsion systems.

Improvement of Flux Deflection With Light-Weight Magnetic Material

Intensified magnetic flux generated by high-temperature superconducting (HTS) field-pole magnet has been studied for the key to improve the machine efficiency of industrial application. An increase of the critical current density allows a further improvement of the operating current in HTS ship propulsion motors. In our previous work, an effect of flux deflection to the critical current of HTS magnet was evaluated. Magnetic flux deflection is a technique to control perpendicular flux to the a-b plane of the HTS tape by magnetic material. Thanks to the magnetic properties of the material, heat loss reduction was confirmed. In this paper, the outcome of the verification experiment with a lightweight magnetic material FINEMET adopted as magnetic flux deflector will be described. In response to the results which increase of the total weight of HTS winding by mounting a magnetic material, weight reduction of the magnetic flux deflector is necessary for practical employment. Compared with the carbon steel, FINEMET has higher saturation magnetic flux density and higher permeability. I-V curve was measured while a pair of the magnetic flux deflectors were installed on the prototype HTS coil connected to the DC current source. In the case of adopting light-weight magnetic material, the reduction of heat generation was confirmed to be 27% which is equivalent to the previous material. At the same time, a weight reduction of 73% was achieved. Results show that FINEMET is effective to improve flux deflection. It is one of feasible material which can be adapted to the field-pole magnet of practical HTS propulsion motor.

High-Power Dense Electric Propulsion Motor

This paper describes the results of design and analysis studies performed by the authors for the comparison of predicted performance of an electric propulsion motor using conventional and emerging technologies. Specifically, a modern squirrel-cage-induction-motor design is compared to both a permanent-magnet motor with high energy magnets and a high-temperature superconducting (HTS) motor using a second generation (2G) superconductor. The selected baseline design is a ship propulsion motor in operation rated at 5000 hp and 1800 r/min. The results of the calculated performance and comparative studies among the various technologies show great potential for increasing the power density using the 2G HTS technology. Using the currently available 2G superconductor current capabilities, the achieved power density of the propulsion motor is twice that of the induction motor. Further investigations are being carried out to improve the superconductor performance for future designs for an ongoing project sponsored by the United States Department of Energy to reduce the cost of the superconductor for future commercial applications of the HTS technology.

Race-track coils for a 3 MW HTS ship motor

Since the discovery of high-temperature superconductivity (HTS), Sumitomo Electric has been developing silver-sheathed Bi2223 superconducting wire and products. Ship propulsion motors are one of the most promising applications of HTS. Sumitomo Electric Industries, Ltd. (SEI) has recently manufactured 24 large racetrack coils, using 70km long DI-BSCCO wires, for use in a 3MW HTS motor developed by Kawasaki Heavy Industries, Ltd. (KHI). The 3MW HTS motor, using our newly developed racetrack coils, has successfully passed the loading test. It is particularly important that the HTS field coils used in ship propulsion motors can withstand the expansive forces repeatedly applied to them. As racetrack type coils have straight sections, the support mechanism they require to withstand expansive forces is very different from that of circular coils.Therefore, we ran tests and obtained the basic data to evaluate the 20-year durability of racetrack coils against the repeatedly applied expansive forces expected in domestic ship propulsion motors.

Marine Asynchronous Propulsion Motor Parameter Identification Using Dynamic Particle Swarm Optimization

This paper proposes a new application of dynamic particle swarm optimization (PSO) algorithm for parameter identification of vector controlled asynchronous propulsion motor (APM) in electric propulsion ship. The dynamic PSO modifies the inertia weight, learning coefficients and two independent random sequences which affect the convergence capability and solution quality, in order to improve the performance of the standard PSO algorithm. The standard PSO and dynamic PSO algorithms use measurements of the mt-axis currents, voltages of APM as the inputs to parameter identification system. The experimental results obtained compare the identified parameters with the actual parameters. There is also a comparison of the solution quality between standard PSO and dynamic PSO algorithms. The results demonstrate that the dynamic PSO algorithm is better than standard PSO algorithm for APM parameter identification. Dynamic PSO algorithm can improve the performance of ship propulsion motor under abrupt load variation.

Analysis of mechanical characteristics of superconducting field coil for 17 MW class high temperature superconducting synchronous motor

Superconducting field coils using a high-temperature superconducting (HTS) wires with high current density generate high magnetic field of 2 to 5 [T] and electromagnetic force (Lorentz force) acting on the superconducting field coils also become a very strong from the point of view of a mechanical characteristics. Because mechanical stress caused by these powerful electromagnetic force is one of the factors which worsens the critical current performance and structural characteristics of HTS wire, the mechanical stress analysis should be performed when designing the superconducting field coils. In this paper, as part of structural design of superconducting field coils for 17 MW class superconducting ship propulsion motor, mechanical stress acting on the superconducting field coils was analyzed and structural safety was also determined by the coupling analysis system that is consists of commercial electromagnetic field analysis program and structural analysis program.

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.

Helium-Neon Gas Mixture Thermosyphon Cooling and Stability for Large Scale HTS Synchronous Motors

Commercial high-temperature superconducting (HTS) wires restrain us to an operation temperature ranging from 20 to 40 K for field-pole magnets applied to rotating machinery. We have proposed to employ a mixture of helium and neon gas in a closed-cycle thermosyphon based on a GM cryo-refrigerator. In this paper, we discuss the temperature stability of the evaporator created by a helium-neon mixture cooling coupled with a closed-cycle thermosyphon, upon an external heat load on a 100-kW-grade HTS synchronous machine. A home-made cooling system, including the condenser, was designed. The evaporator was assembled within the motor in accordance with thermal and mechanical analysis. The cooling of the evaporator with the 100-kW-grade HTS synchronous motor was applied against a variable heat load equivalent with the actual HTS rotor field poles. We report these results and propose its potential application to a large-scale ship propulsion motor.

Electrical Design of a 17 MW Class HTS Motor for Ship Propulsion

A superconducting motor shows several advantages, such as smaller size and higher efficiency, over a conventional motor, especially utilized in ship propulsion applications. However, the size reduction merit appears for large capacity, more than several MW. We develop a large capacity synchronous motor with a rotating high-temperature superconducting (HTS) coil, that is aimed to be utilized for ship propulsion, so it has a low 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 a large magnetic flux that results in a large amount of expensive HTS conductor for the field coil. In this paper a 17 MW HTS motor for ship propulsion is designed with a cost-effective method because the HTS conductor cost is a critical factor in the construction of an HTS motor. Unlike conventional rotating machines, the superconducting motor consists of an iron-coreless structure. Most conventional motors can be designed with small error based on two-dimensional magnetic field analysis. However, the superconducting motor shows an even larger error between the two- and three-dimensional based designs. Thus, in order to improve the design accuracy, we have calculated the back electromotive force (EMF) using 3D magnetic field analysis. An output performance evaluation has also been carried out to obtain a design with higher efficiency.

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.

Reduction of Thermal Loss in HTS Windings by Using Magnetic Flux Deflection

Abstract Efforts on the generation of intensified magnetic flux have been made for the optimized shape of HTS winding applications. This contributes to the high efficiency of the rotating machines using HTS windings. Heat generation from the HTS windings requires to be suppressed as much as possible, when those coils are under operation with either direct or alternative currents. Presently, the reduction of such thermal loss generated by the applied currents on the HTS coils is reported with a magnetic flux deflection system. The HTS coils are fixed together with flattened magnetic materials to realize a kind of redirection of the flux pathway. Eventually, the magnetic flux density perpendicular to the tape surface (equivalent to the a-b plane) of the HTS tape materials is reduced to the proximity of the HTS coil. To verify the new geometry of the surroundings of the HTS coils with magnetic materials, a comparative study of the DC coil voltage was done for different applied currents in prototype field-pole coils of a ship propulsion motor.