Nine-Phase Generator

While the vast majority of high power electric motors and generators are designed as three phase machines, there are applications for which a higher phase order machine is appropriate. The Center is currently engaged in a project in which a nine-phase generator with power levels in excess of 1 MW demonstrated useful performance characteristics. H. Jordan, R. Zowarka, and S. Pratap presented a paper, “Nine-Phase Armature Windings Design, Test and Harmonic Analysis,” which summarizes some of the novel aspects of the system design. The paper was given at the 2004 Electromagnetic Launch Conference.

For further information, please contact R. Zowarka.

Cooling Pulsed Generators

As pulsed generators are reduced in size and weight to improve the power and energy density, active cooling of the windings using flowing water is increasingly attractive. This technology is used successfully in utility generators at power frequencies. The higher frequencies used in these pulsems of charge generation and transport from those found at utility frequencies. Thus a system has been developed to test coolants under these new sets of conditions. The test apparatus was described in the paper, “Empirical Data on High Flow Rate Coolants in Copper Tubing and the Effects on the Coolant’s Electrical Resistivity.” The paper was authored by J. Hahne, H-P Liu, C. Hearn, and J. O’Rarden and was presented at the 2004 Electromagnetic Launch Conference.

For further information, please contact Jon Hahne.

Composite Gun Barrel

In an electromagnetic gun establishing an arc, called transition, rather than maintaining solid metal-to-metal sliding contact will naturally occur if the rails are not held in place during launch. Advances at the Center in the design and manufacturing of composite structures with highly predictable mechanical properties now make it possible to engineer a high quality barrel with mechanical properties needed to eliminate this source of transition. A key factor is assembly using overlapping composite bandings with graded mechanical properties. The important features of the design were summarized in the paper, “Ultra-Stiff, Low Mass, EM Gun Design,” by M. Werst, J. Kitzmiller, C. Hearn, and G. Wedeking that was presented at the Electromagnetic Launch Conference in May 2004.

For further information, please contact Mike Werst.

Pulsed Power – Lite

Many applications of pulsed power systems would be improved if the size and weight of the power system were reduced. With this in mind, a study was done to explore the performance per unit weight of generators used to produce pulses of 20 seconds or less. Generators of this type are frequently used to pulse charge banks of capacitors to generate short high-power pulses. The specific question addressed was fundamental differences in performance if a permanent magnet or a wound rotor were used. The study showed, for the same weight of material (including the exciter for the wound rotor), the wound rotor produced a higher air gap magnetic field and thus the greater output. The general approach and three cases studies were described in the paper, “Pulsed Power Electromechanics – Permanent Magnets versus Copper Coils, “ by K. Davey and R. Hebner presented at the Power Modulator Conference in May 2004.

For further information, please contact Kent Davey.

Cool Bearings

Magnetic bearings are very attractive for high-speed rotors operating in vacuum, e.g. modern flywheels. Since cooling a rotor levitated in a vacuum is a challenge, it is important to minimize the bearing losses while maintaining a high level of performance. To address this challenge, M. Pichot and M. Driga developed design strategies to reduce magnetic bearing losses. Their work is summarized in the paper, “Loss Reduction Strategies in Design of Magnetic Bearing Actuators for Vehicle Applications,” which was presented at the 2004 Electromagnetic Launch Conference.

For further information, please contact Bob Hebner.

Advanced Manufacturing of Novel Alternators

The design of the first-of-a-kind alternator for a specific condition typically requires two-dimensional analysis to quickly rank alternatives followed by rigorous three-dimensional electromagnetic and mechanical modeling. In addition, key manufacturing data is needed for rapid prototyping. The Center has developed a technique to automate this process for the electrical windings to permit efficient design optimization. The process is described in the paper, “Geometric Modeling and EM Analysis of Electrical Windings for Pulsed Alternators,” presented by G. Wedeking at the Electromagnetic Launch Symposium in May 2004.

For further information, please contact Greg Wedeking

Electrical Insulation – Long Life at High Speed

One approach to making electric motors and generators smaller and lighter is to operate them at higher rotational speeds and higher electrical frequencies. The evolution of power electronics makes this an attractive option in a growing number of situations. A concern, however, is some data suggests higher frequency accelerates aging. Working with properly prepared epoxy samples, data has been taken that shows, between 50 Hz and 1000 Hz, the frequency dependence of the onset of partial discharges is very small and likely attributable to thermal rather than direct electrical effects. Thus, in this case, accelerated aging should be negligible. This work was reported in the paper “Frequency Dependence of Partial Discharge Initiation Voltages with Embedded Electrodes,” by A. Wilder and R. Hebner presented at the 2004 IEEE Power Modulator Conference.

For further information, please contact Aleta Wilder.

Medical Uses of Magnetic Fields

Magnetic fields can be used to stimulate the passage of sodium and potassium through nerve cell walls. Devices based on this physical process have been approved by the Food and Drug Administration for use under specific conditions. A newly published paper by Dr. Kent Davey summarizes the fundamental operation of these devices. The paper highlights the processes at the cell level and how those processes lead to requirements on the imposed magnetic fields. He also discusses electric circuits that can be used to produce the needed magnetic fields. The paper, “Pulsed Magnetic Therapy for the Treatment of Incontinence, Disuse Atrophy, Muscle Spasm, and Muscle Reeducation to Increase Mobility,” was included in the book Bioelectromagnetic Medicine, edited by P. J. Rosch and M. S. Markov, and published by Marcel Dekkar in 2004.

For further information, please contact Kent Davey.