4 research outputs found
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Self Excitation of Iron Core Homopolar Generators
In the interest of reducing homopolar generator (HPG) auxiliary requirements, a self-excited field coil for pulsed duty, iron-core HPG has been developed and tested at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). In order to minimize rotor energy expended during excitation, a low-resistance, low-inductance coil was desired to allow field current to rise as rapidly as possible. A seven-turn field coil, having a nominal resistance of 500 µΩ was fabricated for the CEM-UT compact HPG system tester and subsequently tested. At 6,000 rpm, a field current rise time of 1 s was achieved and resulted in an average peak field density of 1.94 T. Only 300 kJ, about 13% of the 2.27 MJ stored in the rotor was required to fully excite the generator.Center for Electromechanic
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Testing of a Homopolar Generator, Energy Storage Inductor, Opening-Switch Railgun System
The first homopolar-fired railgun system was operated in Canberra in 1972 [1,2]. Since that time two additional systems have been tested, the EMACK homopolar generator (HPG) built by Westinghouse and operated by Army Research and Development Center (ARDC) [3] and the joint effort by The Center for Electromechanics of The University of Texas (CEM-UT) and General Dynamics in 1982 [4]. This paper describes the homopolar railgun system operated by CEM-UT in 1985. The aspect that makes this system different from the previous experiments is the design of a fast opening switch (10 to 20 µs) that will allow operation of the HPG into hypervelocity launchers.Center for Electromechanic
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Instrumentation for EM Launcher Systems
This paper reviews the techniques found successful for the measurement of current, voltage and velocity in electromagnetic (EM) launcher experiments at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Current measurement methods using shunts, current transformers, and Rogowski coils are presented and discussed. Special attention is given to the construction and calibration of Rogowski coils and their integrators. Voltage measurements by means of high impedance voltage dividers and current transformers are reviewed. Finally, velocity measurements are presented, with attention to obtaining reliable measurements from time-of-flight velocimeters and ballistic sleds.Center for Electromechanic
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High Coulomb Single Stage Opening Switches
Homopolar generators (HPGs) are modern day energy stores capable of producing large currents (megamps). The generators are typically low voltage, high-capacitance devices with correspondingly slow rise times, and so are unable to directly drive loads requiring fast rise times. A switch must be provided to first transfer energy from the HPG to an inductive energy store and then open to commutate the current to the load. Charging an inductive energy store with large currents for long times requires a massive switch to provide low charging resistance, yet the switch must open and commutate the current to the load in tens of microseconds, typically a feature of a light, fast-acting device. The use of explosives allows the integration of both features in single-stage switch. The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed two high coulomb, single stage opening switches for rai lgun applications. The first switch is a monolithic aluminum element with machined stress concentrations actuated by 100 gr/ft detonating cord; the second uses reloadable cartridges mechanically clamped and explosively actuated with 15 gr/ft detonating cord. Both switches develop in excess of 1 kV/gap with comparable long term holdoff. This paper reviews the development and excellent performance of these switches.Center for Electromechanic