39 research outputs found
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Shaft Signals Corresponding to Cracked Rotor Bars of Induction Machines
Ratings of induction machines range from tens of thousands horsepowers to fractional horsepowers. Unexpected downtime of large Induction motors, such as those used in power plants, can be very costly. Cracked rotor bars of induction machines may overheat rotors, lower outputs, and cause non-retrievable damages.Center for Electromechanic
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Effect of Temperature on Wear Rate of Homopolar Pulse Consolidated Electrical Brush
Binderless copper-graphite composite electrical brushes are being developed using a high-energy, high-rate pulse sintering technique by the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Experiments were done to investigate temperature's effect on the homopolar pulse consolidated (HPC) brush wear rate for an apparent brush current density of 180 A cm−2, a brush downforce of 44.5 N, and rotor surface sliding speeds of 10 m s−1 and 40 m s−1. At a sliding speed of 10 m s−1, it was found that brush wear rate dropped steeply as the brush bulk temperature increased from 80 °C to 103 °C. Other than this unusual wear finding in this particular sliding speed and temperature range, test results indicated that brush wear rate generally increased with increasing brush bulk temperature. At a sliding speed of 40 m s−1, it was found that brush wear rate suddenly increased by several times as the brush bulk temperature approached 149 °C. In the case of 10 m s−1 sliding speed, no stepwise rise in brush wear rate was observed even as the brush bulk temperature reached 156 °C.Center for Electromechanic
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AARADCOM/DARPA Compact Homopolar Generator
If electromagnetic (EM) rail guns are to be used to propel substantial projectiles, large amounts of energy must be delivered in a fast, high-current pulse. Homopolar generators (HPGs) store megajoules (MJ) of energy in the inertia of a flywheel and then .electromagnetically convert this energy into megampere (MA) current pulses that typically have a duration between a thousandth of a second and a second. These machines appear to be the most likely power supply for military rail guns, space launchers, and other large EM propulsion schemes. However, HPGs now exist only as large prototype fixed installations. In order to serve as field power supplies, HPGs must be suitably designed for production, have reduced auxiliary requirements, and generate more power and store more energy per unit mass than the present generation of HPGs. The Center for Electromechanics at the University of Texas at Austin (CEM-UT) conducted a study comparing variolrs HPG operating schemes and machine configurations.C1] The study concludedthat R. A. Marshall's all-iron-rotating (A-I-R) concept (figure 1) in which most of the magnetic circuit is rotated, maximizing energy density, is the best HPG configuration for powering a military rail gun.Center for Electromechanic
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Assembly and Testing of a Compact, Lightweight Homopolar Generator Power Supply
Center for Electromechanic
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Research and Development of High Performance Current Collectors for Homopolar Generators
Over the past five years three homopolar generators (HPGs) have been operated in our laboratory under a variety of experimental conditions. Two of the machines were routinely used as pulsed power supplies, the third machine is an experimental facility for the development of HPG components. Because of the Center for Electromechanics at The University of Texas at Austin (CEM-UT) recent move into a new facility, all three of the machines have been disassembled and inspected offering a wealth of information on the performance of high-slip-speed, high current- density current collectors. Wear rates of sintered, copper-graphite brushes running on steel slip rings as a function of current density and slip speed will be presented along with effects of slip-ring surface finish, using the brushes as a switch to close the electrical circuit and direction of current transfer. Funding for this research has been provided by the U. S. Army Research and Development Command (ARDC), Defense Advanced Research Projects Agency (DARPA), National Science Foundation (NSF), and the Texas Atomic Energy Research Foundation (TAERF).Center for Electromechanic
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Future Trends in Pulsed Power Technology in the Center for Electromechanics, The University of Texas At Austin
Center for Electromechanic
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Homopolar Pulsed Welding: Interface Properties of High Strength Steel Pipe, a Technical Note
This note discusses the microstructure, hardness, and toughness of a homopolar weld (HPW) performed on API 5L grade X-52 line pipe (90 mm diameter and 10 mm wall thickness). Homopolar welding is a solid state welding process made possible by a large pulse of direct current from a homopolar generator (HPG) The heat generated by electrical resistance leads to complex phase transformations resulting in different structures with different characteristics. The results show the weld properties are affected by the pipe materials and that HPW is a promising process for joining high strength steel pipe.Center for Electromechanic
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Design And Testing of a Continuous Duty Current Collectors
The Center for Electromechanics at The University of Texas at Austin (CEM-UT) is involved in brush research to develop sliding electrical contacts capable of high current density (2 kA/cm2), high slip speed (200 m/s), continuous operation. The preferred approach is to actively cool the contact by introducing a coolant into the brush-rotor interface. Preliminary testing of this concept has been performed with encouraging results. Design of a contact will be presented along with test results from a single point brush tester capable of 200 m/s slip speed with externally supplied current Results from the high speed brush tester (HSBT), a homopolar generator capable of 400 m/s operation, will also be presented.Center for Electromechanic
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Homopolar Pulsed Welding for Offshore Applications
Center for Electromechanic
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Homopolar Pulsed Welding for Offshore Applications
As a low impedance energy-storage device, the pulsed homopolar generator (RPG) is capable cif delivering a multimegawatt, megampere-current pulse into a resistive or inductive load with high efficiency. Such HPGs have been used for over ten years as power supplies for research in high energy, high-rate processing of metal alloy components and systems. Most of these processes rely on resistive heating during the current pulse to rapidly heat the material as required for a particular process. One such application is homopolar pulsed welding (HPW), a solid state, forged welding process in which heat generation is concentrated at the interface between workpieces as homopolar current is conducted between them. Because of the very high peak current and power (from 8 to 20 kNcm2 and 50 to 100 kW/cm2), weld time is very short, reducing time-at-temperature exposure and related microstructural changes. Welding is accomplished in air, no flux or filler is used, and the interface disappears completely in a good weld. This paper reports on recent and ongoing research into the weldability by HPW of various alloys applicable to offshore systems, including stainless steel and titanium alloys, but primarily focusing on carbon-steel pipe. This research includes an investigation of weld parameters, sensitivity of the process to the weld parameters, metallurgical and mechanical evaluation of weld quality, and the development of a real-time quality assurance capability that can certify nondestructively an HPW weld before it is removed from the welding fixture. The research presented here is sponsored by the National Science Foundation (NSF) and various private industry companies.Center for Electromechanic