Browsing by Subject "switch"

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Application of a High-Throughput Enantiomeric Excess Optical Assay Involving a Dynamic Covalent Assembly: Parallel Asymmetric Allylation and ee Sensing of Homoallylic Alcohols
(2015-08) Jo, H. H.; Gao, X.; You, L.; Anslyn, E. V.; Krische, M. J.; Jo, H. H.; Gao, X.; Anslyn, E. V.; Krische, M. J.
Asymmetric Ir-catalyzed C-C coupling of primary alcohols with allyl-acetates, as described by Krische, to form chiral secondary homo-allylic alcohols were performed in parallel as a means to optimize the ee values thereof. Specifically, approximately 400 examples of this reaction were performed by varying the catalyst, added acids and bases, and starting reactants, to form 4-phenyl-1-butene-4-ol (1). The ee values for the transformations were determined in a high-throughput fashion using a 4-component assembly that creates a circular dichroism signal indicative of the extent of asymmetric induction. Further, a parallel and rapid quantitative TLC method measures the yield of each reaction, revealing which reactions give reliable ee values in the CD-based assay. Overall, the nearly 200 reactions whose ee values were determined could be quantitated in under two hours. Using a combination of the TLC method to measure yield with the CD-assay to measure ee values, several trends in reaction conditions were revealed. For example, it was found that the cyclometalated iridium catalyst modified by BINAP and m-nitro-p-cyano-benzoic acid delivered adduct 1 with the highest levels of enantiomeric enrichment (94%), whereas the corresponding SEGPHOS-modified catalyst gave a comparable yield but lower ee (91%). Most importantly, this study shows that supramolecular assemblies can report hundreds of ee values in a rapid and reliable fashion to analyze parallel synthesis routines.
Design and Construction of a Two-Stage Opening Switch
(IEEE, 1986-11) Rech, B.; Zowarka, Jr, R.C.
Homopolar generators (HPGs) are modern day energy stores (megajoules) capable of large currents (megamps). The generators are typically low voltage and large capacitance, disallowing loads requiring fast rise times to be driven directly by the HPG. An opening switch must be provided to first, in the closed state, transfer energy from the high current source to an inductive energy store and then open to commutate the current to the load. To charge an inductive energy store with large currents for long times (hundreds of milliseconds) indicates a massive switch with many low resistance contacts. At the same time the switch must commutate current to the load in a short time interval (tens of microseconds) indicating a light, fast-acting device. A two-stage opening switch addresses these two conflicting requirements. The first stage is a massive mechanical switch of coaxial geometry with many low resistance galvanic contacts, which commutates through a low inductance to an explosive element second stage. The second-stage switch is then interrupted explosively to provide the microsecond commutation. The design, manufacture, and testing of the two-stage opening switch were performed at the Center for Electromechanics at The University of Texas at Austin (CEM-UT) Taylor Hall facility in Austin, TX, using a compact homopolar generator (CHPG) and a five-turn coaxial, cryogenic inductor as the pulsed power supply. Initial testing included mechanical actuations and electrical measurements to verify fundamental operation and proper assembly. Testing continued with the CHPG charging the inductor through the switch statically (no commutation) to characterize the current carrying capability of the primary galvanic contacts. Next, tests to check the ability of the first stage to commutate to the second stage by sliding the primary contacts onto the armature insulator were conducted. The fourth phase of testing was a series of two-stage (double) commutations to a fixed load to characterize performance and timing of triggers, voltage hold-off capability, and fixed load commutation times. The fifth and last phase of testing involved the two-stage switch commutating current to a variable impedance (railgun) load.
An Efficient Switch Model for Simulating Large Power Systems with Many Power Converters
(0000-00-00) Uriarte, F. M.; Mashayekh, S.
Frequent matrix factorizations due to power electronic switch commutations are computationally expensive. This paper addresses this burden by treating power electronic switches as dependant sources instead of time-varying resistors. The resulting network matrix is constant, and does not require re-factorization when switches commutate. Three power electronic switches are presented and discussed for both nodal and mesh equation formulations. A case study at the end shows that the run-time for a power system with >200 switches when using the switching approach presented herein can reduce from 8 hours to under 15 minutes, which is a speedup of 40x.
Experimental Data on High Power Explosive Opening and Closing Switches at CEM-UT
(IEEE, 1989-06) Sledge, R.L.; Hahne, J. H.
The need for high power switching i n pulse power research has lead to the development of fast acting opening and closing switches with current capacity of more than 1 MA. Presented is the performance data of two switches developed for railgun experiments at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). The first is a compact closing switch, explosively actuated, used as an isolation device for staging parallel inductors charged by homopolar generators (HPGs) and as a crowbar to shunt excess energy from railguns during projectile exit .The second i s an explosive opening switch which provides a low resistance path during inductor charging before quickly opening to transfer energy to the railgun.
High Coulomb Single Stage Opening Switches
(1987-06) Rech, B.M.; Sledge, R.L; Nalty, K.E; Ingram, M.W.
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.
High Current Making Switch
(1975-11) Wildi, P.
A fast making (closing) switch for high currents is described. It was built to test a homopolar generator developed at the University of Texas. The switch is laid out to carry 300 kA for 3 seconds. It is pneumatically operated and can be tripped without transferring any valves; consequently timing is precise and fast. The contacts are designed to avoid arcings and for minimal inductance. Contact pressure is enhanced by the electromagnetic forces of the current. Tests on the prototype were carried to 550 kA. Oscillograms of the tests are shown. This prototype confirmed the validity of the design criteria and forms the basis for future designs.
High-Current Busbars for a Prototype Homopolar-Toroidal Magnet System for Fusion Ignition
(American Nuclear Society, 1991-05) Sledge, R.L.; Brunson, G.W.; Carrera, R.; Hsieh, K.T.; Weldon, W.F.; Werst, M.D.
The Ignition Technology Demonstration (ITD) is a full torus, scaled prototype of the 20 T toroidal field (TF) coil of the proposed fusion ignition experiment IGNITEX. The 0.06 scale in linear dimension is based on the linear relation between the peak current of an existing power supply (9 MA) and the current required to produce a 20 T field in the fullscale machine (150 MA). Presented here are the design and performance of a busbar and switch which have successfully transferred a total current of 6.75 MA to the ITD during a 15 T experiment. Design considerations included thermal and electromechanical stresses, material properties in liquid nitrogen, electrical resistance and inductance, and physical integration with the existing power supply. The ITD is driven by a 60 MJ, 9 MA power supply consisting of six 1.5 MA homopolar generators (HPGs) located in the Center for Electromechanics at The University of Texas at Austin (CEM-UT).
Power Electronics in the 9 MJ EM Range Gun System
(1991-06) Thelen, R.F.; Price, J.H.
The Center for Electromechanics at the University of Texas at Austin (CEM-UT) is developing an open range demonstrator electromagnetic (EM) gun system with specific size and mass constraints. The design being pursued includes a single phase full bridge rectifier and inverter to accomplish a self generated field excitation and regenerative field energy recovery. The peak power of the excitation system is over 600 MW, performing for single second operations at a repetition rate of once every 20 s over 3 min. The design also includes a solid-state thyristor switch for firing the railgun. This switch closes for one half cycle of ac current, reaching over 3,000,000 A and lasting up to 6 ms. The open circuit rms voltage is 4.2 kV at 125 Hz. These power electronics subsystems have been designed to be compact and lightweight. This paper presents the design parameters, packaging, and control strategies employed.
Soft switching drive for a megawatt class, variable speed, motor/generator
(2007-03) Gattozzi, A.L.; Thelen, R.F; Williams, A.S.
An auxiliary resonant commutated pole (ARCP) converter, rated for an output of 2 MW at 250Hz, has been built and is undergoing tests at the Center for Electromechanics (CEM) of the University of Texas at Austin. The converter is the bi-directional link between a power DC bus and an energy storage flywheel driven by an induction motor/generator. This paper highlights the technical solutions implemented at CEM to insure proper functioning of the ARCP converter when driving various electrical loads including the 2 MW 15,000 rpm induction motor/generator are reported. A new topology for a soft-switching converter is also proposed that addresses many of the issues encountered in the course of this development and some comparisons are made regarding the application of soft-switching ARCP-type converters versus their hard-switched counterpart.
Switch Development At UT-CEM
(IEEE, 1985-06) Peterson, D.R.; Zowarka, R.C.; Rech, B.M.
Two reusable (with replacement of a few expendable components), fast (tens of microseconds), megampere switches operated with commercially available explosive charges suitable for indoor laboratories are described. One is a low-inductance, triggerable opening switch and the other, a metal-to-metal self-assisted closing switch. The opening switch is the second stage of a two-stage switch for storage inductor commutation. The first stage is a heavy-duty mechanical switch. The explosive switch itself has a number of stages in series which can be fired simultaneously, for high voltage, or sequentially for millisecond pulses into loads of time-increasing impedance (electric guns). The closing switch is actuated by projection of a metal ring into the tapered gap between coaxial electrodes. The switch is simple, self-contained, readily scaled to larger sizes, and fast enough for crowbarring electric guns. Large ring mass (>100 g) enables heavy-duty uses such as crowbarring homopolar generators.
Switching Overview--Fundamental Issues
(IEEE, 1984-03) Woodson, H.H.;
Good afternoon. It is a pleasure to be here and an honor to be asked to overview and chair this switching session. I feel unprepared for the task, because I have much less experience than those on the program in designing, building, and operating switching systems, and I am sure the same is true with respect to almost everyone in the audience as well. Nevertheless, I have an active interest in switching, and I am involved technically with a group working on switching problems. These have led me to think about fundamental problems of switching. I wil share with you briefly my thoughts on a few of what I consider to be the most fundamental and difficult issues in switching. I hope that these thoughts will be useful to you as you continue your efforts to improve your switching systems. As we all know, switching is the process by which a branch in an electric circuit changes from being a very good conductor (ideally a short circuit) to being a very poor conductor (ideally an open circuit), or vice versa. There are applications that require both closing and opening switches, and each has its own set of fundamental issues. The interest here is almost entirely in opening switches, so I wil confine my remarks to those. The switching system envisioned here for a discussion of fundamental issues is one which carries current for a relatively long time, typical of charging a storage inductor from a homopolar generator, and then transfers the current to a load in such a short time that circuit inductance dominates the current transfer. After current transfer; the switch must withstand the voltage of the load.