High Temperature Superconducting Motor Research Articles

${\rm I}_{\rm c}$ and AC Loss of 2G YBCO Tape Measurement for Designing and Fabrication of an HTS Motor

This paper presents a new synchronous motor whose stator uses 2 High Temperature Superconducting (HTS) pancake-coils wound from 2G HTS tapes and 4 conventional copper coils, while the rotor contains 75 bulk HTS elements. All superconducting materials are cooled by liquid nitrogen (77 K). The HTS and copper armature includes 3 phase circuit and is mounted in the slots of a nonmagnetic and insulating material. Each phase winding, fabricated in the form of a pancake-coil, is distributed in slots of 60-degree intervals. YBCO melt-textured pucks were incorporated into the rotor and the reluctance was tested. In addition, a unique cooling system using a copper conductor is designed, which is similar to that of a superconducting flywheel. Finally, we present and analyse results on measuring DC critical current and self-field AC loss in HTS tape supplied by American Superconductor. The measurement systems are described. The results on the AC loss measurement of YBCO samples are presented and analyzed within the framework of the critical state model.

Design of an HTS motor

This paper gives a detailed description of the design of a high temperature superconducting (HTS) motor. The stator of the motor consists of six air cored HTS racetrack windings, together with an iron shield. The rotor is made of 80 superconducting YBCO pucks, which can be magnetized and equates to a four-pole permanent magnet. The whole HTS motor is cooled by liquid nitrogen to 77K, and acts as a permanent magnet synchronous motor with the power rate of 15.7 kW.

Development of an HTS motor with Ho-123 superconducting field coils at liquid nitrogen temperature

A 22kW, 360RPM, 8-pole high temperature superconducting (HTS) synchronous motor with Holmium (Ho)-123 field coils at liquid nitrogen temperature was designed, manufactured and tested. This motor employs an axial gap rotating-armature construction and consists of one field assembly and two armature assemblies. The field employs eight single pancake coils which are wound with the world's first developed Ho-123 HTS wire. Ho-123 wire has potential high critical current density, which is expected to be as large as 100 times of BSCCO wire. Each coil is wound with 15m wire and the field can carry 75A current at liquid nitrogen temperature. We investigated coils AC behaviour and proposed a new way to minimize AC loss. A new method to suppress field current ripple is employed in this motor. A large variety of motor experiments were carried out and compared to the 3D model analysis that was conducted by Finite Element Method (FEM) showing the results met all its design goals. This paper provides the key designs of the motor, the analysis, tests of field coils and the motor.

Scaling Up of HTS Motor Based on Trapped Flux and Flux Concentration for Large Aircraft Propulsion

A high temperature superconducting (HTS) motor has been designed to power a general aviation aircraft. The propulsion requirements of the Cessna 172 have been chosen as baseline for the study: 200 HP at 2700 RPM. The designed motor is based on flux trapping in bulk YBCO plates and concentration of the flux generated by Bi-2223 coils and an ironless air-cooled resistive armature. The eight-pole machine would exhibit high power density comparable to that of small gas turbines around 4 HP/lb. Details of this HTS motor concept have been presented in a previous paper. However, the scaling up of such a configuration is not straightforward, as single domain YBCO elements cannot exceed a few centimeters in diameter. This paper presents the design of a motor based on the same configuration but with a much higher power rating, in the range of several MW, to power high altitude long endurance (HALE) aircraft or small jets. Due to the size limitation of the YBCO plates, two solutions can be used to increase the power: the radius and the number of poles can be increased, or the motor can be lengthened to accommodate more coil-plate pairs. The motor is able to reach more than 2 T in the air gap thus leading to high power density. The design optimization is done with respect to several objectives as a trade-off between amount of superconductor, efficiency, weight and volume. The cooling system is assumed to be provided by liquid hydrogen available onboard the aircraft as fuel for the fuel cells or turbo-generators.

Quench in High-Temperature Superconducting Motor Field Coils: Computer Simulations and Comparison With Experiments

For high temperature superconducting (HTS) motor field coils two types of quench initiation are of practical importance. The first type will be referred to as current induced quench (CIQ). It typically occurs during coil or assembled rotor testing, when the current is increased in small increments until the quench is detected. The current at which the quench starts is referred to as the quench current Iq [1]-[7]. The objective of these experiments is to establish actual limits of operational conditions. The second type will be referred to as temperature induced quench (TIQ) and it is caused by failure or malfunctioning of the cooling system. The examples include vacuum deterioration, cryocooler failure etc. Numerous CIQ experiments [1]-[8], [10] have showed a certain pattern of quench event, including a well defined Iq, slow near-linear increase with respect to time of coil voltage and temperature with subsequent transition to fast non-linear voltage and temperature growth. TIQ experiments [10] showed the same behavior when coil cooling system was shut down while the current was maintained constant. The presented here work is a computational 2-D and 3-D Finite Element Analysis (FEA) study of CIQ and TIQ in HTS coils. The effects of magnetic field, non-homogeneity of tape properties, current sharing and amount of stabilizer are studied. It is shown that the formation and propagation of the normal zone is preceded by the process that we chose to call pre-quench instability. The pre-quench instability starts when the current exceeds Iq and demonstrates experimentally observed features mentioned above. It is shown that with an insufficient amount of stabilizer for second generation (2-G) HTS tapes the pre-quench instability may be practically undetectable. The comparison with some of the experiments [8], [10] is presented. We intensively used the concepts developed in articles [1]-[6]. Many (but not all) our conclusions are in agreement with [1]-[6].

Quench in High-Temperature Superconducting Motor Field Coils: Experimental Results at 30 K

The results of quench tests on high-temperature superconducting (HTS) motor coils conduction-cooled to 30 K are presented. In previous tests, the same coils were cooled by direct immersion in liquid nitrogen. In spite of both a significantly lower temperature and a different cooling mechanism, the 30 K tests confirm the previous results which showed that the quench process is characterized by a current level, referred to as the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">quench current</i> , above which the cooling system cannot maintain the winding temperature. Currents in excess of this value will produce an unstable growth in winding temperature in a process commonly referred to as a coil quench.

Mechanical design of a synchronous rotating machines with Gd-Ba-Cu-O HTS bulk pole-field magnets operated by a pulsed-field magnetization with armature copper coils

We studied a high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk pole-field magnets. The structure of a HTS motor is an axial gap type with neither brushes/slip rings nor iron core. The specific feature is that the rotor pole-field magnets of bulk are magnetized with pulsed current flow through vortex-type armature copper windings. The rotor pole bulks and armature coils are cooled down with liquid nitrogen. Cooling and magnetization of bulk pole field magnets are performed inside of the rotor. The trapped peak magnetic field of more than 0.5 T of the bulk magnets provided the motor performance of 3.1 kW with 720 rpm. In order to attain high output, single rotor plate with 8 bulks was substituted with a twinned rotor plates with 16 bulks together with triple layer armature units. We report on the test results and performance of the present twinned rotor-type HTS synchronous motor.

Effect of Synchronous Reactance and Power Factor on HTS Synchronous Machine Design and Performance

Synchronous reactance is an important parameter of synchronous rotating machine because it affects on the machine output capacity, voltage variation and steady-state stability. The superconducting synchronous rotating machine has very small synchronous reactance about 1/5 of the conventional synchronous machine. This reason comes from the fact that the superconducting rotating machine is air-cored structure. In this paper, it is estimated how much this synchronous reactance has influences on many design parameters of superconducting synchronous machine such as machine volume and weight, efficiency, voltage variation and so on. In the case of a synchronous motor, the power factor can be adjusted according to the excitation voltage. This paper also deals with the effects of power factor on the design parameters and the performance of a HTS (High-temperature Superconducting) synchronous motor. This kind of analysis was used to design 1 MW class HTS motor

High Temperature Superconducting Motor Power Density Improvements

The use of high temperature superconducting (HTS) wire technology enables magnetic shear stress improvements in rotating machinery as high current densities can be achieved. The use of HTS wire, however, requires a large effective magnetic gap due to the use of full air-gap style stator windings as well as thermal insulation and electro-magnetic shielding to maintain HTS rotor coil operating temperatures within required limits. Due to these large magnetic gaps, HTS machines require large pole pitches to maximize the flux that links stator coils. Large pole pitches result in low pole numbers, which increase stator core and support structure weight. The use of a partial air-gap stator winding (CW-EMD patent pending) in an HTS motor effectively reduces the magnetic gap, which results in increased flux linkage with stator conductors. Reductions in the effective magnetic gap allow for the selection of smaller pole pitches and thus weight savings.

HTS Motors in Aircraft Propulsion: Design Considerations

Current high temperature superconducting (HTS) wires exhibit high current densities enabling their use in electrical rotating machinery. The possibility of designing high power density superconducting motors operating at reasonable temperatures allows for new applications in mobile systems in which size and weight represent key design parameters. Thus, all-electric aircrafts represent a promising application for HTS motors. The design of such a complex system as an aircraft consists of a multi-variable optimization that requires computer models and advanced design procedures. This paper presents a specific sizing model of superconducting propulsion motors to be used in aircraft design. The model also takes into account the cooling system. The requirements for this application are presented in terms of power and dynamics as well as a load profile corresponding to a typical mission. We discuss the design implications of using a superconducting motor on an aircraft as well as the integration of the electrical propulsion in the aircraft, and the scaling laws derived from physics-based modeling of HTS motors.

The Performance of a 5 MW High Temperature Superconductor Ship Propulsion Motor

A 5 MW, 230 RPM, 6-pole high temperature superconductor (HTS) ship propulsion motor is presently under test at the Center for Advance Power Systems (CAPS). This paper provides a summary of the key design features of the motor, predicted performance, factory test results and extended test results to date at CAPS. This motor was designed and built under the U.S. Navy's Office of Naval Research (ONR) funding (Contract #N00014-02-C-0190) to address the next generation of electric ship propulsion systems. HTS motors are characterized by high power density, quiet operation and high efficiency. HTS air-core motors have unique electrical characteristics and therefore require dynamic testing to validate all modes of operation. The test program at CAPS is designed to address dynamic performance and simulation of this class of propulsion motor. The motor has been operated at 5 MW load for over 3 hours at CAPS.

Characteristic study and three dimensional magnetic field analysis of the superconducting synchronous machine

The field distribution analysis and the characterization of racetrack magnet for LTS (low temperature superconductor) generator and HTS (high temperature superconductor) motor were performed. An SSM (superconducting synchronous machine) have two structural characteristics: they have similar air-cored structures which function to avoid saturation at an iron-core; the process of keeping superconductor cold and insulated leads to a long air-gap length. For those reasons, the SSM is featured by three dimensional (3D) magnetic flux distribution, which varies in the direction of axis. An analytical method to analyze more fast and accurately the effect of the shape of the field coil on the 3D magnetic field distribution, was studied. The 3D magnetic field distribution of the SSM (LTS generator and HTS motor) was calculated using the analytical method, and then the results were verified by experiment and 3D finite element method (FEM).

An Approach of Optimal Design of HTS Synchronous Motor Using Genetic Algorithm

This paper describes an optimal design of 100 HP, 4 pole, 1800 rpm high temperature superconducting (HTS) synchronous motor in terms of energy efficiency and downsizing, i.e., specific power density. Bi-2223/Ag multifilamentary tape is used as a material of HTS field coil. Design variables and constraints are appropriately set up in consideration of electromagnetic characteristics. Size of the rotor and the stator is calculated with fundamental expressions based on the two-dimensional electromagnetic analysis. As an optimization technique to obtain the dimension of optimal specific power density or energy efficiency of the HTS motor, genetic algorithm (GA) which is well-known as aglobal optimal technique modeled on the concept of natural selection and evolution has been used. Electrical characteristics such as efficiency and V-curve for the HTS motor optimally designed are also investigated.

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.

Design of field coil for 100 hp class HTS motor considering operating current

The value of critical current (I/sub c/) in High Temperature Superconductor (HTS) tape is greatly influenced by perpendicular magnetic flux density B/spl perp/. Therefore, I/sub c/ of HTS magnet is determined by not only operating temperature but also the B/spl perp/. In this paper, flux distribution and operating current are calculated according to the field coil change in 100 hp class HTS motor. The magnetic flux density of field coil is calculated by changing the outer radius and inner width of field coil. Biot-Savart equation is used as analytic method for the characteristic analysis of magnet. 3D FEA (Three Dimensional Finite Element Analysis) is used for the magnetic field distribution in the HTS motor. The operating current of 100 hp class HTS motor is calculated by using I/sub c/-B/spl perp/ curve.

Method for estimating future markets for high-temperature superconducting power devices

This paper describes a spreadsheet model for estimating the impact of high-temperature superconducting (HTS) power devices on the national electric grid. The distribution of losses in the national grid is carefully traced and those losses that HTS can eliminate are identified. The energy savings achievable by the many sizes of HTS generators, transformers, cables, and motors are then computed and totaled using a spreadsheet analysis. The economic savings are very sensitive to the price (and J/sub e/) of HTS wire, and to the cost of cooling the devices to operating temperature. A market penetration model is used to estimate how fast HTS devices become commercially,successful. The emphasis of the paper is the analytic tool, not the numerical results of one specific case. This entire model is explicitly designed to allow others to enter their own estimated parameters and arrive at their own conclusions.

High output power reluctance electric motors with bulk high-temperature superconductor elements

We present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS)—YBCO and Bi–Ag—elements. We discuss different schematics of hysteresis, reluctance, ‘trapped field’ and composed synchronous HTS machines. The two-dimensional mathematical models describing the processes in such types of HTS machines were developed on the basis of the theoretical analysis of the electrodynamic and hysteresis processes in the single-domain and polycrystal YBCO ceramic samples and plate shape Bi–Ag elements. We give the test results of the series of hysteresis, reluctance, ‘trapped field’ and composed with permanent magnets HTS motors with an output power rating of 0.1–18 kW and current frequencies 50 Hz and 400 Hz. These results show that in the media of liquid nitrogen the specific output power per one unit weight of the HTS motor is four to seven times better than for conventional electric machines. A comparison of the theoretical and experimental characteristics of the developed HTS motors show that they are in good agreement. We discuss the test results for a liquid nitrogen cryogenic pump system with a hysteresis 500 W HTS motor. We describe several designs of new HTS motors operating in the media of liquid nitrogen with an output power 125 kW (and more) and a power factor of more than 0.8. We discuss future applications of new types of HTS motors for aerospace technology, on-land industry and transport systems.

Application of response surface methodology to robust design for racetrack type high temperature superconducting magnet

This paper describes an approach to robust design of the field coil shape for High Temperature Superconducting Motor (HTSM), considering the maximum B/spl perp/ reduction to enhance the robustness. The robust design to reduce the maximum B/spl perp/ should be considered in order to maintain the stability and substantial improvement on the performance of HTSM. The approach is based on the Response Surface Methodology (RSM) and the estimated model is used to minimize the total sensitivity of design variables. A validity of this approach is verified through comparing the robust solution with the normal result obtained by a conventional optimization procedure.

The Hunt for Compact Power

This article explains features of a ship propulsion motor with superconducting coils that hushes machinery noise and hollows out confined engine rooms. American Superconductor Corp. of Westborough, MA, announced plans to build a high-capacity manufacturing plant for its superconducting wire. This will move the company’s high temperature superconductor (HTS), wire from a developmental phase into large-scale production. IPS is exploring more than just propulsion motor technology. Engineers are evaluating the entire shipboard electrical system, from ship’s service power, to dc distribution, to power electronics—as well as the propulsion motor itself. The Navy, having decided upon electric drive for its next warship, has left the door open for superconducting motors. Superconducting motors can develop the same torque and horsepower within a motor frame that is nearly a third the size of a comparably rated conventional motor. The main factor leading to an HTS motor’s smaller size for a given horsepower output is the magnetic field strength that superconducting magnets create. Iron teeth, used to enhance magnetic flux in conventional rotors and stators, are not needed by superconducting motors.

High-Temperature Superconducting Motor Using Y-Ba-Cu-O Bulk Magnets

A DC motor equipped with melt-processed Y-Ba-Cu-O (YBCO) superconductors as field magnets was constructed. The YBCO bulks were magnetized at temperatures of 65-77 K in a liquid nitrogen vessel by applying a pulsed magnetic field. The maximum output power was 940 W when the YBCO bulks were cooled to 65 K. Continuous running tests were carried out for up to 6 h. We found that the trapped magnetic fluxes are hardly affected by the magnetic field of 7500 A/m generated by the armature current and that cooling of the YBCO bulks to low temperatures is very effective for holding the trapped field at a high level and, hence, substantially elevating the performance of a high-temperature superconducting (HTSC) motor.