Superconducting Field Winding Research Articles

High-temperature superconducting magnet motor demonstration

A superconducting field winding, assembled with coils constructed with Bismuth 2223 HTS wire, has been successfully operated in an electric homopolar motor. At a field winding temperature of 4.2 K, the motor produced 125 kW of output power. At a temperature of 28 K, the motor power developed was 91 kW. These measured power levels are the highest that have been produced by an electric motor containing a HTS field winding.

Preliminary study on a rotating armature type superconducting motor

A rotating armature type motor with a laboratory made four pole saddle shape superconducting field winding has been constructed. Cool-down tests were carried out successfully several times. By the motor operating as a generator under no load and resistive load conditions, machine constants are obtained. The air gap field with outer magnetic shield yoke is 29% higher than without yoke. The field coil could stand current up to 120 A. The rated terminal voltage should be 220 V for 1800 rpm (at 90 A field current). The armature coil could stand current up to 50 A, with a rated armature current value of 40 A corresponding to 15 kW at 0.98 power factor. Moreover the experimental and theoretical characteristics of the motor will be presented. >

DC motors with high-critical-temperature superconducting field winding and slotless armature

The paper describes the design and characteristics of high-power DC motors combining a superconducting field with a slotless, multiplex armature. This type of armature allows the motor to be designed with ratings much higher than is otherwise possible. The high-critical-temperature superconducting field winding provides a relatively simple, lightweight excitation system. A special winding is proposed as a means of avoiding torque reaction at the field winding and the resulting force which would need to be transmitted through the cryostat. The design of a 1O MW 150 rev/min motor is presented as an example and compared with a conventional design for the same specification. The superconducting, slotless machine has about half the weight and half the loss of the conventional machine.

Field winding model test of 70 MW class superconducting generator

A national project for development of a superconducting generator has been continuing since 1988 in Japan. In this project, the authors have been developing a superconducting field winding. An aluminium stabilized double standard superconducting cable has been developed for the winding. In the rotor, the centrifugal force field is 5000 G, and consequently liquid helium has a cooling ability ten times larger than that in the 1-G gravitational field. Therefore, a cryostable winding design can be used. A field winding model having 40% of the 70-MW-class generator field winding was tested in a nonrotated cryostat. The specification and structure of the cable and the test results are outlined. >

Stabilization of a fully superconducting, damperless generator by excitation control

AbstractThe development of ultrafine filaments superconductors for 50/60 Hz makes possible a fully superconducting generator which has superconducting field windings and armature windings. By omitting dampers and narrowing gaps between the field and the armature windings, the size and the weight of the fully superconducting generator can be drastically decreased. However, the damperless generator is inherently unstable and thus must be stablized by an appropriate method. We have investigated a method of stabilizing the generator in which the excitation voltage of the field winding is controlled by the state value feedback technique. The state values of the system are estimated by a state‐value observer and the feedback constants are determined according to optimal control theory. It is shown that this method is effective in stabilizing a fully superconducting, damperless generator.

４８０ｋＷ舶用超電導直流単極電動機の試作特性

The superconducting electric propulsion system using superconducting motor seems to be an ideal propulsion system for the future. We have constructed a 480kW superconducting DC homopolar motor for the purpose of developing this new system. This motor is composed of superconducting field winding, segmented armature drum and copper-graphite current brushes. The superconducting field winding is cooled by the condensation heat exchangers and helium refrigerating system being built into the cryostat. We have obtained good test results that operating parameters of this DC homopolar motor accorded with the design parameters.

Characteristics of superconducting generator at high response excitation

Superconducting generators have many advantages, one of which is their ability to improve the stability of power systems because of their low synchronous impedances. The advantage may be increased by adoption of high-response excitation. The first 100 kVA high-response excitation superconducting generator has now been built. One of the problems in the design of such generators involves the characteristics of the field circuit, i.e., the field armature winding, losses in the component materials, and loss in the superconducting field winding. In this paper, a 2-dimensional electromagnetic field analysis of field circuit characteristics is presented.

Practical Design of Superconducting Generator. Electrical and mechanical design.

Since a superconducting generator (SCG) consists of a superconducting field winding, a nonmagnetic cryogenic rotor and an airgap armature winding, its design method differs from that of the conventional generator. Practical applications require establishment of its electrical and mechanical design methods.A design flowchart of the SCG was shown and the basic design method was clarified. For this method, the electrical and mechanical design of a 50MVA experimental generator was carried out. Its design specifications and size were compared with a future 1, 120MVA generator and a 778MVA conventional generator. Furthermore, synthetic stress applied on the main rotor components, such as the torque tube and room temperature damper, was obtained. From the test results of generator power loss and the V curve under synchronous condenser operation, the design method was proved to be valid.

Transient shielding effect of slitted electrothermal shield of superconducting generator

An electrothermal shield with direct axis directional slits is proposed for application to a superconducting alternator with quick-response excitation system. Using the finite element method combined with external circuit equations, short-circuit characteristics due to slitting effects are investigated by comparing three cases, conventional electrothermal shield (CES), slitted electrothermal shield (SES), and no electrothermal shield (NES) models, under three phase fault and line to line fault, respectively. The field current variations, flux densities in the vicinity of superconducting field winding, and the eddy currents of the SES model are computed and then compared with those of the CES and NES models. It is expected that the superconducting alternators with SES could adopt the quick-response excitation system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of magnetic fields in the slotted structure of a superconducting AC generator

An analytical model has been developed to help determine the distribution of the magnetic flux density inside the superconducting AC generator. The model takes into account the number, and the geometric structure, of the winding slots and allows the rotor of the superconducting machine to be designed with optimum magnetic field distribution. The results obtained by the model are verified by comparison with results obtained by former models. The new model is also used to study the influence of the field winding geometry on the magnetic flux density distribution. The paper also reviews two-dimensional modelling methods for calculating the magnetic field inside a superconducting AC generator, and highlights some of the problems and opportunities for the application of these methods to magnetic field analysis of superconducting field winding.

Development and characteristics of superconductor for 70-MW class high-response excitation superconducting generator

The superconducting field winding of the 70-MW classhigh-response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle-shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force. The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low-loss high-current density superconductor will be able to be applied to the field winding of the 70-MW class high-response excitation superconducting generator.

Normal zone propagating characteristics and stability criterion of the superconducting field windings for a test rotor

An outline is given of a constructed model rotor and the preliminary experimental results are described. The model rotor was excited up to a rated current of 2000 A without training. The normal zone propagating velocities were measured in a rotating cryostat and were also calculated using the estimated heat transfer coefficients. By considering the change in the voltage drops after the normal transition, minimum burn-out current were found. If the operating current is smaller than this current, the conductor will not burn out even after the normal transition. This minimum burn-out current could be used as a safety current criterion.

Stability tests against thermal disturbances on rotating superconducting field windings

A superconducting test rotor was constructed and the transient stabilities of the field windings were studied. They were evaluated at various centrifugal accelerations up to 2000 g and it was found that the field windings with bare strands were extremely stable against transient disturbances, and that the insulator coating on the strands might be very detrimental from the viewpoint of both steady state and transient stabilities. It was also clarified that both the minimum film boiling and maximum nucleate boiling heat fluxes were considerably increased, even inside a slot under large centrifugal acceleration, and that these increases contributed to the improvement of stability of the windings. It was shown that even a small cooling channel inside the windings could be effective for cooling.

Influence of converters on the superconducting field-circuit of a three-phase synchronous generator

Experimental investigations of the influence of converter feeding the field circuit of a three-phase synchronous generator with a superconducting field winding have been performed. Four converter circuits have been tested: a B6 three-phase bridge, two parallel B6 three-phase bridges, a three-phase bridge with bypass thyristors, and a high-current power-MOSFET converter. Steady-state and transient operation have been tested. There was a special interest in the harmonics generated by the converter circuits and their power dissipation in the low-temperature region. The thermal reaction of the field circuit has also been considered. A method has been developed to prevent the superconducting winding from the quenching in transient operation.

A system for quench detection in the superconducting field winding of a synchronous generator

In order to protect the superconducting field winding of a model synchronous generator against thermal destruction during a quench, the voltage differentials between two parts of the field winding are measured. In practice this method of quench detection is not good enough, as contrary to theory, normal dynamic operation in itself causes significant voltage differentials. The behavior of electrical transmissions within the excited field and armature circuits producing voltage differentials are identified. A process computer is used to simulate these voltage differentials in real time. It is also necessary to use an observer to compensate for the time drift which occurs between the real winding behavior and the digital parallel model. Only significant deviations between measured and simulated signals indicate a quench and release an emergency shutdown of the generator.

超電導発電機の界磁エネルギー制御による電力系統の安定化

The advantages of synchronous generator with superconducting field winding can be stated as: (1) Reduction in losses, (2) Improved system performance, (3) High-Voltage armature feasibility, (4) Small size and weight. Some feasibility studies have been carried out, and currently some model machines for demonstration are under construction.The superconducting field winding which produces strong magnetic flux can be viewed as an energy storage and its application to power system stabilization has been proposed and the damping effect of power swing has been confirmed numerically.In this paper an improved control scheme for power system stabilization which has the function of voltage regulation by the control of field winding current, is proposed. Some numerical examples demonstrate that the proposed system is capable of suppressing the voltage fluctuation as well as damping power oscillation, significantly. Furthermore, the specifications of the superconducting generator necessary for the stabilization of a model power transmission system are estimated in detail. In the case of 1, 120MVA generator with 24MJ stored energy at 6kA rated field current, the maximum DC voltage is 3, 300V, the maximum rate of field current change (dI/dt) is 3, 500A/s and the maximum power exchanged between the field winding and the power system is 20MVA.

7万kW級超速応励磁形超電導発電機用導体の開発と特性

The superconducting field winding of the 70-MW classhigh-response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle-shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force. The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low-loss high-current density superconductor will be able to be applied to the field winding of the 70-MW class high-response excitation superconducting generator.

超電導発電機の研究開発状況

The application of superconducting technologies to electric power apparatuses is very important from the viewpoint of not only the promotion of energy and resources saving but also the improvement of power system stability. Super-GM was established in September, 1987 in order to proceed the research and development (R & D) on application of superconducting technologies to power apparatuses and Super-GM R & D project, which is sponsored by New Energy and Industrial Technology Development Organization (NEDO) under the Moonlight Project of Industrial Science and Technology, Ministry of International Trade and Industry, started from FY 1988 for a scheduled period of eight years. As to R & D on superconducting generator, the basic designs and analyses of 70MW class model machines and the research on element techniques concerning superconducting field winding, structural materials of multi-cylindrical rotor, warm damper, rotating cooling characteristics, helium transfer coupling and air gap armature winding of superconducting generator were conducted in FY 1988 and 1989, and many basic results were obtained. At present, R & D step is proceeding steadily from the research on element techniques to the examinations for manufacturing techniques using partial models such as field winding model, multi-cylindrical roter model, rotating cooling model, helium transfer coupling model and armature winding model for the manufactures and demonstration tests of 70MW class model machines. In this paper, the current situation of R & D on superconducting generator carried out by Super-GM is presented.

高遠心力環境下で動作する超電導式ヘリウム液面計の制御電流

Superconducting field windings of superconducting generators are cooled with liquid helium which forms a cylindrical surface in the rotating helium pool. It is important for superconducting generators to ensure the detection of the liquid level to prevent an accidental transition of superconducting field windings into the normal state. Superconductive helium level detectors are used to measure the helium level in the rotating helium pool. It is important in general for superconductine helium level detectors to select a suitable control current. So we tried to investigate the suitable control current experimentally using a rotating cryostat. As a result we found that the control current of superconductive helium level detectors should be about two times bigger under circumstances of high centrifugal acceleration than that which is usually selected under circumstances of 1G.

Practical experience on the operation of a 320 kVA synchronous generator with a superconducting field winding

Eight years of experiments carried out on a 320-kVA two-pole, external-pole-synchronous generator with a superconducting field winding. A summary is presented of practical experience and empirical results, which were obtained in 39 test cycles. On back-strokes, difficulties and problems concerning the generator and the whole test setup are reported as well as successes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>