HTS Trapped Field Magnet-Based Motors for Naval Applications
High Temperature Superconductor trapped field magnets (TFM) have matured to the point that they now offer serious possibilities for significantly increasing power density in electromechanical devices.
Among the more significant problems solved are creepage of the field and cracking of the material, and fields of over 18 T demonstrated. The remaining problem of how these materials can be charged in situ both before and subsequent to cooling was described in the paper, “HTS Trapped Field Magnet-Based Motors for Naval Applications,” by K. R. Davey of the Center for Electromechanics and R. Weinstein of the University of Houston Beam Particle Dynamics Laboratory. Additional attention was given to how this material might be used as a slot liner to increase the mutual coupling between the rotor and stator while reducing leakage. The paper was presented at the Electric Machine Technology Symposium 2006. The requirements for accomplishing in situ charging are significant. For further information, please contact Kent Davey.
Vector B field if the current excitation is increased to 1.16 • 106A.
Induction Motor Performance Testing with an Inverter Power Supply
The development of high power density electrical machines continues to accelerate, driven by military, transportation, and industrial needs to achieve more power in a smaller package. Higher speed electrical machines are a recognized path toward achieving higher power densities.
Existing industry testing standards describe well-defined procedures for characterizing both synchronous and induction machines. However, these procedures are applicable primarily to fixed frequency (usually 60 or 50 Hz) power supplies. As machine speeds increase well beyond the 3,600 rpm limitation of 60 Hz machines, a need for performance testing at higher frequencies is emerging.
An inverter power supply was used to conduct a complete series of tests on two induction motors (0.5 MW and 1.0 MW) with speeds up to ~5,000 rpm. The use of a non-sinusoidal power supply with limited power output capability required the development of measurement techniques and testing strategies quite different than those typically used for 60/50 Hz testing.
Instrumentation and techniques for measuring voltage, current, and power on harmonic rich waveforms with accuracies approaching 1% are described. Locked-rotor and breakdown torque tests typically require large kVA input to the motor, much higher than the rated load requirement. An inverter sized for the rated load requirements of the motor was adapted to perform locked-rotor and breakdown torque tests. Inverter drive protection features such as anti-hunting and current limit that were built into the inverter had to be factored into the test planning and implementation.
Test results were presented in two companion papers, “Induction Motor Performance Testing with an Inverter Power Supply: Part 1,” and “Part 2,” by Howard E. Jordan, Raymond C. Zowarka, Thomas J. Hotz, and John R. Uglum, and presented in poster format by Howard Jordan at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006. Part 1, which correlates test results with the results of an algorithmic induction motor analysis program, was published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 242-245. Part 2, which presents the test results compared with a Matlab™ simulation program and provides a comprehensive discussion of the instrumentation that was essential to achieve testing accuracy, was published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 275-278.
Correlating test results with calculated values confirmed that the testing techniques developed during this testing program are useful for evaluating high speed, high power density electrical machinery. For further information, please contact or Ray Zowarka.
Motor test area
Field Coil Insulation Testing for Pulse Power Alternators
Current pulse power alternator designs operate at high speeds and high current densities. The field coil insulation systems for pulse power alternators must provide sufficient stand-off voltage, while limiting the amount of thermal resistance for actively cooled designs, and also withstand the strain excursions experienced at full operating speed. Repetitive cycling of the strain excursion overtime may induce cracks in the surrounding field coil matrix. The primary insulation surrounding the field coil conductors must be able to stop crack propagation that may develop in the surrounding matrix material and provide voltage hold-off. Thermally conductive thermoplastics are currently being investigated for the field coil matrix materials where decreased thermal resistance is necessary for actively cooled field coil designs.
In order to evaluate conductor insulation and thermoplastic matrix filler quickly, small coupon motorettes were developed per previous designs. The motorettes simulate the hoop strain the conductors would experience due to rotor growth at high rotational speeds. Once the motorettes had been mechanically loaded, the coupon was hi-potted to verify insulation integrity under strain. A paper, “Field Coil Insulation Testing for Pulse Power Alternators,” by Clay S. Hearn, Jon J. Hahne, Steven M. Manifold, and Scott P. Pish and presented in poster format at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006, discusses the design and testing of these motorettes to evaluate thermally conductive thermoplastics as filler material for the field coil matrix. This paper was published the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 234-237. For further information, please contact Clay Hearn.
Stand-alone test stand fixture designed to apply simultaneous pull force and electrical potential to transverse coupon sample. |
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Coordination of Large Pulsed Loads on Future Electric Ships
Part of the technical versatility of future all-electric ships is the potential ability to share large amounts of power among a variety of high power loads. To help evaluate this potential and to provide information to help guide technology selection, a physics-based model of a power train for an electric ship was developed and implemented on three modeling platforms. Using this model, three different investigations were carried out to explore aspects of the behavior of a rotating machine power source for a shipboard rail launcher. These were 1) influence of rapid charging of the rotating machine system on the ship power system, 2) use of the stored energy in the rotating machines to improve ship power quality, and 3) use of the stored energy in the rotating machines to power a pulsed free-electron laser.
Each study highlighted different integration opportunities and challenges. The first showed that, because the charging of the rail launchers was through 5 MW motors, there could be a voltage sag for a few cycles, but this could easily be managed so that the sag could be reduced to an inconsequential level. The second study showed that, with appropriate power electronics, the stored energy in the rail launcher power supply can be used to correct power quality problems introduced by other ship systems. Finally, the stored energy in the launcher power supply can be used to fire a free electron laser for ship defense. This feature opens the possibility of routine operation of the entire ship at highest efficiency, i.e., with the smallest number of gas turbines operating near full power, while providing stored energy needed for ship defense.
This was described in a paper, “Coordination of Large Pulsed Loads on Future Electric Ships,” by Lori N. Domaschk, Abdelhamid Ouroua, and Robert E. Hebner (Center for Electromechanics) and Oscar E. Bowlin and W. B. Colson (Naval Postgraduate School, Monterey, California), which was and presented by Robert Hebner at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006 and published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 450-455.
For further information, please contact Robert Hebner.
Notional power system for future electric ship.
Structural Properties and Testing of a Composite Banding Used in High-speed Rotors
The use of high strength structural composite bandings is essential for high-speed rotors. In addition to bandings designed for maximum stiffness and strength, there is also a need for bandings that exhibit a controlled radial growth during operation. Controlling the radial growth rate of rotor bandings to match the growth of other rotor components maximizes the structural integrity of the rotor by minimizing reaction forces between parts during operation. A paper, “Structural Properties and Testing of a Composite Banding Used in High-speed Rotors,” by Vasileios Lelos, Steven M. Manifold, and John J. Granier, presented in poster format at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006 and published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 250-253, presents the structural material properties and strain-to-failure of a composite banding built with a layup consisting of high strength IM7 hoop filament windings and a combination of T700 tape laid at 0° and ±45°. The analysis and structural test results used to determine the strength of a composite banding with the non-traditional 100% hoop wound layup is discussed in this paper.
For further information, please contact Steve Manifold .
Field Initiation Design Fundamentals for Pulsed Alternators
Efficient high performance pulsed alternator (PA) systems have low impedance field windings that rely on very fast current rise times in order to maintain attractive system efficiencies. These systems rely on positive feed back self-excitation, or ‘boot-strapping’ action, to energize the field winding. The self-excitation process is typically started by a small capacitor-based power supply which is discharged (or seeded) directly into the field winding. The design of this power supply, often called the Field Initiation Module (FIM), is critically important to the process of self-excitation.
Augmented by numerical simulations, a paper, “Field Initiation Design Fundamentals for Pulsed Alternators,” by Jon R. Kitzmiller and Mircea D. Driga, examining the important aspects to consider when designing a proper FIM, including impact on system efficiency, minimum rotor speed for proper FIM function, control schemes for triggering the FIM, and proper operating voltage for the FIM, was presented in poster format at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006 and published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 246-249. For further information, please contact Jon Kitzmiller.
Thermoplastic Applications for Pulse Power Alternators
The field coil is the primary component of the rotor assembly that provides the rotating magnetic field for the pulse power alternator. The design of the field coil is optimized so that it will produce the required magnetic field with minimum transient losses. The high currents required to produce the correct amp-turns, along with the mechanical loads due to high rotational speeds, present further design requirements for selection of field coil material, insulation, and surrounding material that completes the matrix of the field coil sub-assembly. With the addition of active cooling requirements in the field coil design, surrounding materials must be selected that retain electrically insulative properties and are thermally conductive to allow sufficient heat removal from the field coil.
Thermoplastics are now being reviewed to replace traditional glass-epoxy potting compounds (thermosets) that have been used extensively in pulsed alternator designs. Fillers can be added to tailor properties of the thermoplastic, such as ceramics to increase thermal conductivity at the cost of an increase in density. Thermal analyses have been performed that show the benefits of using thermally conductive potting compounds. In addition, subscale field coil mock-ups (motorettes) have been encapsulated and tested to demonstrate encapsulation of current field coil geometries.
This information is discussed in a paper, “Thermoplastic Applications for Pulse Power Alternators,” by Clay S. Hearn, Jonathan J. Hahne, Hsing-Pang Lui, and Michael D. Werst and was presented in poster format at the 13th Electromagnetic Launch Technology Symposium in Potsdam, Germany in May 2006 and published in the IEEE Transactions on Magnetics, vol. 43, no. 1, January 2007, pp. 238-241. For further information, please contact Clay Hearn.
Flat minicoil wrapped with three half-lap wraps of Kapton® CR film |
