Homopolar Generator Research Articles

Analysis of Performance Improvement of Passenger Car Synchronous Homopolar Generator with the Addition of Ferrite Magnets

Electric machines with hybrid excitation have increased torque density while maintaining a wide range of speed control. This article presents the results of the optimal design of a synchronous homopolar generator (SHG) with ferrite magnets on the rotor and excitation winding on the stator for passenger cars. The use of ferrite magnets on the rotor of a synchronous homopolar generator makes it possible to use the stator surface more efficiently, which in turn increases energy efficiency and reduces the dimensions of the generator. At the same time, the excitation winding on the stator provides a reliable brushless design and the ability to control the excitation flux. The problem of long-time calculation of the three-dimensional SHG structure, which is especially relevant when using multi-iterative computer optimization, is solved by using the computationally efficient Nelder-Mead method and a simplified SHG model using two-dimensional finite element analysis. It is also clear that the low torque ripple of SHG with ferrite magnets with two stator-rotor stack combinations (SRSC) is largely provided by the fact that the torque ripples of individual SRSCs are in antiphase. The problem of considering the magnetic properties of magnetic core sections made of structural low-carbon steel is discussed. It has been found that with an increase in both the saturation level of the magnetic circuit and the magnetomotive force (MMF) of the SHG excitation winding, resistance to irreversible demagnetization of ferrite magnets on the rotor can be increased by increasing their height. In addition, it is shown that there is a significant increase in performance when using the hybrid excitation, in comparison with the conventional SHG design without magnets.

Synchronous Homopolar Generator without Permanent Magnets for Railway Passenger Cars

The article presents the optimal design of a 35 kW brushless synchronous homopolar generator without permanent magnets for railway passenger cars. The excitation winding of the generator is located on the stator, and the toothed rotor has no windings. The generator characteristics are optimized considering the required constant power speed range. A single-objective Nelder–Mead algorithm and 2D Finite Element Analysis were used for the optimization. As a result of the optimization, power losses are significantly reduced over the entire operating range of the generator rotational speed, the current capacity of the solid-state rectifier, and the torque ripple. A comparison of the calculated characteristics of the generator under consideration with the characteristics of a commercially available undercar generator shows that the active volume is reduced by a factor of 2.1, and the losses are significantly reduced over the entire operating speed range.

Improvements in modern weapons systems: the use of dielectric materials for the development of advanced models of electric weapons powered by brushless homopolar generator

Although the idea of making electric weapons has emerged since the beginning of the 20th Century, the great number of technological problems made that such technology was not developed. During the Cold War, the US strategic programme Space Defensive Initiative paid a special attention to this category of weapons, but the experiments have demonstrated that the prototypes are too big, very heavy, and involve a very high energy consumption and low reliability. Under these circumstances, the authors have noticed the trend to design new types of electric weapons starting from the hybridization of some technologies: the compressed flux weapons, the plasma electromagnetic cannon, the electromagnetic weapons as the coil-gun and rail-gun.

Westinghouse EMACK Railgun

Westinghouse Electric Corporation was the early leader in railgun technology in the 1980s and developed the 16 to 30 MJ stored energy homopolar-generator (HPG) powered system, EMACK, which provided the highest muzzle energy of any railgun from 1982 to 1988 during testing at Westinghouse Research and Development Center, Pittsburgh, PA, USA, and after installation at ARDEC, Picatinny, NJ, USA. Details of the design, components, and fabrication of EMACK are provided here, and results from the abbreviated initial testing are included. Many scientists, engineers and technical staff who worked on the project described here some 30 to 40+ years ago have by now mostly retired, moved on to other activities, or sadly, in several cases, are deceased. However, it would be remiss if their pioneering efforts were not recognized, and this article attempts to do that. Prospects for future energy storage and pulsed power developments using HPGs and more recent developments are also discussed.

The handheld and hand-powered homopolar generator

The handheld and hand-powered homopolar generator

Design of a 10-MW-Class HTS Homopolar Generator for Wind Turbines

High-temperature superconductor (HTS) technology has been studied recently for the use with superconducting high-power transmission and distribution, motors, generators, and fault-current-limiting devices such as cables and transformers. HTS technology, which can provide a large electromotive force in a small area owing to its large current density compared to that of a normal conductor, can reduce the weight and loss of a generator when compared to the attributes of a conventional machine. Moreover, once the HTS conductor has stabilized, the challenge of cooling the windings in large-scale generators can be resolved. Therefore, the technology has been studied for application with 10-MW-class superconductor wind-turbine generators. Although an HTS conductor generator offering a higher torque density, lower weight, and higher efficiency than a conventional generator can be designed, the design must satisfy the requirements of the critical magnetic field, critical current, and critical temperature of the superconducting winding. The HTS homopolar superconducting synchronous generators have a simple structure with a fixed HTS conductor and are one of the most suitable types of generator that is able to satisfy these requirements more easily. In this paper, we propose a 10-MW homopolar-type wind-turbine generator.

Energy conservation and Poynting's theorem in the homopolar generator

Most familiar applications of Poynting's theorem concern stationary circuits or circuit elements. Here, we apply Poynting's theorem to the homopolar generator, a conductor moving in a background magnetic field. We show that the electrical power produced by the homopolar generator equals the power lost from the deceleration of the rotating Faraday disk due to magnetic braking and review the way that magnetic braking arises within Poynting's theorem.

A DC Transformer

A component level dc transformer is described in which no alternating currents or voltages are present. It operates by combining features of a homopolar motor and a homopolar generator, both dc devices, such that the output voltage of a dc power supply can be stepped up (or down) with a corresponding step down (or up) in the current. The basic theory for this device is developed, performance predictions are made, and the results from a small prototype are presented. Based on demonstrated technology in the literature, this dc transformer should be scalable to low megawatt levels, but it is more suited to high current than high voltage applications. Significant development would be required before it could achieve the kilovolt levels needed for dc power transmission.

A Homopolar HTSG Topology for Large Direct-Drive Wind Turbines

For offshore wind energy, there is a trend toward larger wind turbines. The increased mass of a power-takeoff system increases the installation cost of the turbine. Direct-drive superconducting generators have the potential to reduce the installation cost of wind turbines. For a successful entry to the offshore-wind-energy market, a high-temperature superconducting generator should be as reliable as conventional generators. It is proposed that a stationary superconducting direct-current-field winding may increase the reliability of the generator. An axial-flux homopolar generator topology is proposed to be used in low-speed high-torque applications. The topology is modified by using two superconducting field windings to obtain a bipolar flux-density distribution for higher power density. Different core types and dimensions were examined to find the most suitable design, and a conceptual design of a 6-MW 12-r/min generator is presented.

Numerical simulation of a complete generator-rail launch system

In this paper, the numerical analysis of a complete launch package, composed by a homopolar generator feeding a rail launcher, is described. Because of the nonlinear and time varying characteristics of both generators and launchers, a separate analysis of the two devices is not always able to provide highly accurate previsions about the performance of the overall system. The analysis has been performed here by using an integral formulation that transforms the Maxwell's equations into an equivalent electric network, whose parameters vary together with the evolution of the system. The presence of sliding contacts and the consequent velocity skin effect in both the generator and the launcher have been taken into account. The most important electromechanical quantities have been reported; the results of the simulations shows the effectiveness of the software used for this coupled analysis.

Fabrication and test of a small experimental superconducting homopolar machine with axially laminated rotor disks

In order to examine the fundamental availability of a homopolar machine with laminated armature rotor disks, the authors fabricated and tested a small superconducting experimental homopolar machine with two rotor disks. The machine was tested as a generator. The obtained experimental data show that the output voltage of the 2-disk machine is about 2 times larger than that of the 1-disk machine. From this experimental result, we can conclude that the output voltage of a homopolar generator with axially laminated rotor disks is proportional to the number of the disks.

Marcus Laurence Elwin ‘Mark’ Oliphant

Marcus Laurence Elwin ‘Mark’ Oliphant

The self-excitation process in electrical rotating machines operating in pulsed power regime

The self-excitation process in pulsed air-core rotating generators is fundamental in assuring record values of power density and compactness. This paper analyzes the conditions for the self-excitation process in pulsed electrical machines used as power supplies for electromagnetic launchers, using the analogy and methods of the positive-feedback in control systems. In the classical ferromagnetic electrical machines in the self-excitation process, the machine output is used in order to gradually excite the generator until the steady-state voltage is finally reached. The end of the process and, consequently, the stability and repeatability, is assured by the intersection of the strongly nonlinear magnetization characteristic and the excitation straight line. In the air-core, pulsed power machines such as homopolar generators and compulsators, the two characteristics are apparently linear and both the end and the initiation of the process must be forced. The paper shows that the pattern of the self-excitation process is very similar in all the EML power supplies (homopolar, compulsators, asynchronous) and the initially unstable process reaches stability in a very controlled way. The paper also shows how the self-excitation can create a new EML power supply with an original use, from a classical electrical machine.

Railgunnery: Where have we been? Where are we going?

The author reviews the way in which the art of modern railgunnery has progressed since it began at The Australian National University about 30 years ago. During the 10-year life of that program, most of the problems fundamental to railguns were encountered and examined. One of the reasons for the success of the ANU railgun program was the existence in Canberra at that time of the very large 500-MJ 1.6-MA homopolar generator. Use of this set the tone for the railgun work as its focus moved to the USA. The progression of power supply thinking from that point on is examined and conclusions drawn. The evolution of the railgun itself is also presented with particular emphasis being placed on armature development. The specifics of the two main armature-rail problems, gouging and transition, are examined in detail. Finally, where we are now is described, and from this vantage point, suggestions for the direction of future work are made.

２１世紀へ伝えたい超電導応用技術 １ 単極発電機

２１世紀へ伝えたい超電導応用技術 １ 単極発電機

Performance simulation of pulsed power supply system for electrothermal launcher

Computer simulation of electrical discharges in the high-pressure chambers of electrothermal launcher pulsed power supply systems containing homopolar generators (HPGs), storage inductors (SIs) and two-stage opening switches with mechanical and explosive circuit breakers has been carried out at the chamber radii of (0.02-0.1) m and various values of the gap spacing (0.1-0.8) m. Space-time dependences of pressure and temperature in the chambers as well as energy losses in the circuit elements are calculated. Up to 40 per cent of the HPG energy is shown to be delivered to the plasma load. Taking it into account, the volume and the mass of a transportable power supply providing the energy input to the load at the level of 5 MJ and consisting of two 6.5 MJ HPGs connected in parallel, a 9 MJ SI, a rotating mechanical circuit breaker as well as an explosive one operating due to the current conducting thin metal cylinder destruction by annular cumulative jets are evaluated. Simulation results of the medium heating and pressure oscillations in the chamber operating at the currents of 200-300 kA through each HPG and energies of 100-300 kJ per shot are presented.

Corrosion behavior of high energy-high rate consolidated graphite/copper metal matrix composites in chloride media

The corrosion behavior of particulate reinforced graphite/copper (Grp/Cu) metal matrix composites (MMCs) was studied in 3.5 wt.% sodium chloride solution using electrochemical techniques, ionic solution analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques. The materials under investigation were high energy-high rate (HEHR) consolidated Grp/Cu metal matrix composites. HEHR processing employs a 10 MJ homopolar generator that supplies a 100 kA pulse to rapidly heat and solidify the composite powder compact. This short time at high temperature and the preferential heating and melting at the graphite-copper interface serve to encapsulate the graphite reinforcement, thus providing a highly densified composite product. Initially the open circuit potential corrosion behavior of 1.2, 5, 15, 25, and 40 volume percent GrpCu composites was studied in aerated and deaerated 3.5 wt.% NaCl solution using SEM and EDX. Subsequently, the environmental stability of these composites was studied using electrochemical techniques such as polarization resistance and potentiodynamic polarization. The severity of corrosive attack increased with increasing graphite content and in aerated solutions. In addition, solutions from these tests were analyzed to determine the relative amounts of copper and carbon present in the electrolyte after polarization tests. Microscopic analysis techniques were used to characterize the corrosion morphologies and the extensive localized corrosion occurring at the graphite-copper interface. The effectiveness of benzotriazole as a corrosion inhibitor for the copper MMCs was also studied.

Homopolar generators for electric guns

Low voltage homopolar generators combined with magnetic energy storage inductors were used to power several early experimental railguns. Over the last 10 years this arrangement has fallen into disfavor for future high-energy railgun systems compared with multipole AC generators, largely because of the need for an opening switch to both transfer high current and open against voltages of a few kV. Basic features of homopolar generators are examined and factors relating to their potential for future electrothermalchemical (ETC) gun systems are considered briefly. The energy and current requirements for such guns are substantially less than for high energy railguns, so that homopolar generators (HPGs) may prove feasible.

The AMT maglev test sled-EML weapons technology transition to transportation

Technology spinoffs from prior electromagnetic launcher work enhance a magnetic levitation transportation system test bed being developed by American Maglev Technology of Florida. This project uses a series wound linear DC motor and brushes to simplify the magnetic levitation propulsion system. It takes advantage of previous related work in electromagnetic launcher technology to achieve success with this innovative design. Technology and knowledge gained from developments for homopolar generators and proposed rail gun are control are key to successful performance. This contribution supports a cost effective design that is competitive with alternative concepts. Brushes transfer power from the guideway (rail) to the vehicle (armature) in a novel design that activates the guideway only under the vehicle, reducing power losses and guideway construction costs. The vehicle carries no power for propulsion and levitation, and acts only as a conduit for the power through the high speed brushes. Brush selection and performance is based on previous EML homopolar generator research. A counterpulse circuit, first introduced in an early EML conference, is used to suppress arcing on the trailing brush and to transfer inductive energy to the next propulsion coil. Isolated static lift and preliminary propulsion tests have been completed, and integrated propulsion and lift tests are scheduled in early 1996.

Development and test of a 300 kW superconducting homopolar generator

A 300 kW superconducting homopolar generator has been jointly developed and tested by the Wuhan Marine Electrical Propulsion Research Institute and the Institute of Electrical Engineering, Academia Sinica. It is a drum-type machine with superconducting excitation and solid brush current collection, 1300 RPM rotating speed, 230-330 V output voltage. The armature rotor diameter is 620 mm, effective length is 600 mm, the average radial magnetic field in the armature region is 0.75 T. During testing, it reached 300 kW nominal output power and worked stably. The design and development of the machine and its main components, together with its test results are presented.