High-Speed Turbine and Generator

At levels up to a few megawatts, gas turbines are small and efficient when their rotational velocity is high, typically between 10,000 and 20,000 rpm. The Center staff members have fabricated a high-speed generator that can operate at the turbine speed to provide for a small power plant for land or sea applications. This system is about the size of a car, yet could provide electricity for more than a thousand homes. The generator and its commissioning tests were described in the paper, “Development of a 3 MW High-Speed Generator and Turbine Drive for a Hybrid Vehicle Propulsion System,” by J. Herbst, R. Thelen, and K. Cook of the Center for Electromechanics and by J. Ranero and D. Bigley of the Naval Surface Warfare Center, Carderock Division. The paper was presented at the ASME Turbo Expo 2005; Power for Land, Sea, and Air, in June. For further information, please contact John Herbst.

Keeping Motors Cool

In the design of novel, high-power-density, motor systems, it is important to control the temperatures throughout the motor so as not to compromise the material properties of the constituent. Electrical insulation materials are particularly sensitive to combined thermal, mechanical, and electrical stresses. Moreover, temporal or spatial average temperatures are only useful if all temperatures are well below operational limits, a situation that does not occur when power density is a critical factor. H-P. Liu, V. Lelos, and C. Hearn published the paper, “Transient 3-D Analysis for an Air-Cooled Induction Motor,” that demonstrates successful detailed modeling of the temperature distribution in a novel induction motor. This paper was presented at the International Electric Machines and Drives Conference in San Antonio, Texas, in May 2005. For further information, please contact Hsing-Pang Liu.

A Smaller, Faster Induction Motor and Generator

The Center for Electromechanics designed and is fabricating and testing a 2 MW induction motor-generator that operates at rotational speeds between 7,500 and 15,000 rpm. M. Caprio, V. Lelos, J. Herbst, and J.Upshaw prepared a paper that described design features, material choices, and novel fabrication techniques that allowed an increase the power output of an induction machine by about a factor of 10 over conventional industrial designs.  The paper titled, “Advanced Induction Motor Endring Design Features for High Speed Applications,” was presented at the International Electric Machines and Drives Conference in San Antonio, Texas, in May 2005. For further information, please contact M. Caprio.

Flywheel Batteries for Hybrid Vehicles

M. Flynn, J. Zierer and R. Thompson recently reported on the performance of a flywheel battery used in a hybrid bus. Flywheel batteries are an excellent technology for this type of application because they can operate longer, more than 100,000 charge-discharge cycles, and require less space than a chemical battery pack. The research reported included determination of energy losses, shock and vibration testing, tests of the flywheel itself, tests of the containment system, and tests on an operating bus. The work was described in a paper titled, “Performance Testing of a Vehicular Flywheel Energy System,” presented at the SAE 2005 World Congress, in April 2005. For further information, contact Dr.Mark Flynn.

Flywheel Standard Issues

A new standard, ANSI/AIAA S-096-2004, for flywheels used in space has been issued. This standard addresses the design, fabrication, testing and inspection of flywheel rotors used in space applications. On earth, flywheels are typically used for energy storage and load leveling. While they serve the same functions in space, they have the additional advantage in space of being useful for attitude control. Richard Thompson of the University of Texas Center for Electromechanics was a member of the committee that developed the standard. In addition, the standard incorporates some of the research results and test approaches first developed and documented at the University. For further information, contact Richard Thompson.

Copper Measurement in Coolant System

A recent study of water as a coolant in an electrical machine has shown that flow velocity and area of coolant tube surface both affect the production of copper in the system. A recent paper, “Limitations on water cooling of rotors and stators in intermittent duty machines,” By C. Hearn, J. Hahne, and R. Hebner in the 2004 Annual Report of the Conference on Electrical Insulation and Dielectric Phenomena, shows that for grounded systems the processes are consistent with classical mobility determinations for copper in water. This investigation provided necessary baseline data for an assessment of the behavior on time scales comparable to the intrinsic time constant of the water. For further information, please contact R. Hebner.

Smoother Power

Flywheel systems are frequently preferred over chemical batteries to provide power to critical installations in the interval between the time the electrical grid fails and an emergency power system can be brought on line . A new flywheel system for that application has been developed that incorporates an improved capability to transition the critical load to the emergency system. In some cases, this new capability may permit the installation of a smaller and more economical emergency system. The flywheel system was designed to provide 125 kW for 20 seconds. This innovative approach to power management was described in a joint paper by M. Flynn of the Center and A. Paylan of Vycon, Inc. The paper titled, “A Novel High-Speed Flywheel Based DC Voltage Source with Soft Handover Capability,” was presented at the International Electric Machines and Drives Conference in San Antonio, Texas, in May 2005. For further information, please contact Dr. Mark Flynn.

Wheel Motors That Handle Bumps Off the Road

Hybrid and all-electric vehicles use electric motors to drive the wheels of the vehicles. These motors, called wheel motors, can be used for acceleration, braking and differential torque steering. E. Triche, J. Beno, H. Tims, M. Worthington, and J. Mock recently released modeling and simulation results that focused on the mechanical shocks that such wheel motors would encounter in off-road uses. The work showed that the forces resulting from the mechanical shocks were more than 100 times the weight of the motor. Having developed this data, they followed by designing a wheel motor that would operate even with mechanical shock forces of 150 times the weight of the motor. This work was summarized in the paper, “Shock Loading Experiments and Requirements for Electric Wheel Motors on Military Vehicles” presented at the SAE World Congress in April 2005.For further information, please contact Edward J. Triche.

Simulations Can Guide Suspension Choices for Future Vehicles

Since 1993, staff members at the Center for Electromechanics have been developing advanced suspension systems for high-speed off-road vehicles. This research has led to the development of advanced simulation capability, validated by hardware demonstrations. This capability was used to assess the likely performance of passive, semi-active, and fully active suspension systems in a 20 ton, 8x8, future military vehicle. The key parameters addressed were driver and crew comfort, crew effectiveness, equipment effectiveness, vehicle control, safety and handling, and energy consumption. As expected, the active suspension scored higher in all of these categories. The data, however, is useful in helping to assess the cost and benefits of each approach by quantifying, on a consistent basis, the benefits. The results were summarized in the paper “Suspension Trade Studies for Hybrid Electric Combat Vehicles” by J. Beno, M. Worthington, and J. Mock presented at the SAE 2005 World Congress in April. The paper was singled out as the paper having the most long-term value of the twelve papers in the Military Vehicle – Vehicle Modeling and Simulation session. For further information, contact Dr. Joe Beno.

Electric Ship Power Systems

The Navy is moving toward the use of all electric ships including the use of an electric gun to replace the large guns currently used on warships. CEM staff members performed an analytical study that shows some advantages to the ship power system of using pulsed alternators as the power supplies for the electric guns on these future ships. The study showed that a pulsed alternator that stored 10 shots was smaller and lighter than a capacitor power supply system that stored a single shot. Moreover, the pulsed alternator could be used as flywheel energy storage to enhance power system performance during the majority of the ship’s life when the guns were not needed. This work was summarized in the paper “An Electromagnetic Gun Power Supply as a Component of an Electric Ship Power System” by R. Hebner, J. Pappas, J. Kitzmiller, K. Davey, J. Herbst, A. Ouroua, and J. Beno. The paper was presented at the High Powered Weapon Systems for Electric Ship 2004 in Annapolis, MD, December 2004. For further information, please contact R. Hebner.