Browsing by Subject "Electric switchgear"

Now showing 1 - 11 of 11
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    Breakdown processes in laser triggered switching
    (Texas Tech University, 1983-05) Dougal, Roger Adelbert
    An investigation of laser triggered switching using a 1.06 µ NdrYAG laser to trigger a uniform field gap filled with 800 Torr of N2 has been performed in the following triggering geometries: 1) Transverse not striking electrodes, 2) Coaxial not striking electrodes, 3) Coaxial striking target electrode, and 4) Coaxial striking recess in target electrode. Streak photography, time resolved spectroscopy, and current measurements reveal great differences in the breakdown processes for the various geometries. The major differences are attributable to laser field interaction with the incipient arc channel. All breakdown processes except types 2 and 3 look quite similar to an overvolted breakdown. Diagnostics of type 2 triggering have shown a laser assisted streamer propagating from the laser fireball to the opposite electrode. Streak photography shows the streamer precursor of the breakdown channel initially proceeds across the gap at a few times 10 cm/sec, but slows to about 2X10 cm/sec as it advances in the focal cone to regions of lower laser intensity. The laser interaction with the streamer produces a uniform, high conductivity channel which emits intense continuum light once ohmic heating raises the channel temperature. When delay is greater than the laser pulse length two distinct regions can be detected in the arc channel; one, laser assisted, showing the abrupt, uniform continuum luminosity, and the other not laser assisted, appearing much like a weakly overvolted breakdown process, exhibiting a glow discharge stage followed by thermalization proceeding from the ends of the glow region towards the middle at 10 cm/sec.
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    Design of a neutral point clamped power inverter
    (Texas Tech University, 1996-12) Crittenden, David Brent
    This thesis details the design, construction, and preliminary testing of a Neutral Point Clamped Power Inverter. The inverter is designed for the 100 kilowatt class of inverters and has a three phase output connection and a neutral connection. The inverter is designed around insulated gate bipolar transistor as the power switching devices. The inverter employs software generation of the gate signals for the power switches and gate driver electronics to ensure reliability and insulation between the high power and low power circuitry. The inverter produces a true three level line-to-neutral voltage waveform and a true five level line-to-line voltage waveform. The true descriptor indicates that a zero voltage output is not produced by averaging two potentials. Rather, a zero voltage output is produced by connecting the output voltage to a neutral point. To date, the inverter has been tested at 20 kilowatts of continuous power.
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    Investigation of shock pressures in high current spark gap electrodes
    (Texas Tech University, 1995-08) Wofford, Michele
    Generally, the limiting component in a pulsed power system is the switch This is due to the fact at some point, the switch transfers all of the energy in the system High voltage and current create a rough environment for switch electrodes and insulators. In previous studies of switch reliability and lifetime, electrode erosion has received much attention. This investigation deals with the mechanisms behind electrode fracture, which presents an immediate problem, rather than erosion, which has long-term effects on switch performance. The switches under study are spark gaps with graphite electrodes. The spark gap closes when an electric arc forms between the electrodes, and current conduction begins Strong mechanical forces are generated as the arc forms and impact the electrodes. The purpose of this research is to determine the dominant pressure mechanism of electrode fracture, and the propagation of the pressure wavefront through the electrode. Energy is stored in a 5 kJ, 60 kV capacitor, and shorted through the spark gap. This is done to duplicate prior experimental work at Physics International Company. Operating parameters, such as gap spacing, air pressure, charging voltage, inductance, and magnetic pulse shaping, are varied, and mechanical pressure is measured using a strain gage mounted on a ceramic bar. Experimental data from the strain gage is compared to theoretical modeling done in Mathcad and PSPICE.
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    Material studies in a high energy spark gap
    (Texas Tech University, 1983-05) Gordon, Lloyd B.
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    Multichannel surface discharge switch
    (Texas Tech University, 1983-08) Johnson, Donald E
    A system designed to investigate the performance of dielectrics in a multichannel surface discharge switch was built and tested. The apparatus consisted of a constant current charging supply that produced 10 mA at 50 kV, a storage capacitor, a 6-ohm stripline, the surface switch, a matched 5-ohra copper sulfate water load, and diagnostics. Diagnostics to evaluate the dielectric performance included capacitive voltage probes in the stripline, a video camera to record multichannel events on videocassettes, and an optically isolated counter to record the number of events in a test run. Typical operating parameters were: 180 joules per pulse, a peak voltage of 40-50 kV, and a peak current of 7 kA. Dielectric samples were tested by placing them in the switch for 19,000 shots at a repetition rate of 1-1.2 pulses per second. The dielectrics were then compared by observing their erosion, changes in breakdown voltage, and the number of channels that occur during discharges. Further analysis to study possible chemical change in the surfaces of three of the dielectrics was performed using Electron Spectroscopy for Chemical Analysis (ESCA).
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    Optically controlled diffuse discharges for switching applications
    (Texas Tech University, 1986-08) Hutcheson, George Zohn
    Diffuse discharges containing electronegative gases, at present, are the only means capable of fast, repetitive, long-life operation as opening switches. Optical control of diffuse discharge switches has been proposed as both a means of sustaining and of enhancing the performance of such switches. Processes considered in this dissertation are photo ionization. photo detachment. and several approaches to optically enhanced attachment. Ultraviolet (UV) ionization has been used for several years now as a means of preionizing self-sustained diffuse discharges and, recently, has been used as a sustainment mechanism for diffuse discharge opening switches. Time-resolved measurements of the optical emission of a spark array, similar to those used for preionization or sustainment of diffuse discharges, are presented. Results of experiments in atmospheric pressure diffuse discharges containing admixtures of attachers, sustained and initiated by such a spark array, are also presented. Photo detachment is considered as a mechanism which could decrease switch losses and decrease switch closure time by counteracting dissociative attachment. Experimental results are presented demonstrating optically increased current densities, of as much as 900%, in externally sustained and externally initiated, atmospheric pressure, diffuse discharges containing 0^. This process proceeds through photodetachment of 0 by 590 nm light generated by a dye laser (0 +hu -• 0+e). Optically enhanced attachment through the generation of vibrationally excited attachers appears particularly attractive as a means to decrease turn-off or opening times for diffuse discharge switches. For some molecules attachment cross-sections can be increased by orders of magnitude by vibrational excitation. The influence of this effect on the resistivity of a discharge through IR pumping of NH.;^ and CpH^aF by a low power CO^ laser in continuous low pressure discharges is presented. UV enhanced attachment is also shown in gases containing molecules such as C^HpF^. CpHpClp, and CpH-Cl where UV photo dissociation produced vibrationally excited, strongly attaching, molecules (e.g.. C2H2F2+hu-C2H2+HF(v>1)).
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    Optically enhanced attachment processes in diffuse discharges
    (Texas Tech University, 1987-05) Holmberg, Courtney Doyal
    During the last several years, interest In high voltage switches for pulsed power applications has increased significantly. One main concern in the field of pulsed power Is that of energy storage. While inductive energy storage systems have space and weight savings when compared with capacitive energy storage systems, they also require the use of a high power opening switch. Therefore, opening switch technology has started to be developed, and several concepts for opening switches are currently being studied. One particular concept is that of the diffuse discharge opening switch, which has several advantages over other types of opening switches. A significant advantage of the diffuse discharge opening switch is that it may be externally controlled by optical means or by an electron beam. In this paper, three experiments are presented which study the use of optically enhanced attachment as a discharge control mechanism in diffuse discharges. The first experiment demonstrates the effect of UV enhanced attachment in an externally sustained discharge. The second experiment shows the effect of IR illumination in a self sustained discharge. The last experiment demonstrates the effect of IR enhanced attachment in an externally sustained discharge. Future experiments in optically enhanced attachment are also discussed.
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    Optimization of the discharge characteristics of an electron beam sustained discharge for opening switch applications
    (Texas Tech University, 1986-12) Korzekwa, Richard A.
    For an opening switch an attaching gas must be used to obtain a fast opening time in a diffuse discharge. In the process of optimizing gas mixtures in an electron beam sustained discharge, three different types of gas mixtures are presented. The first type of gas mixture utilizes one attaching gas, C2F6, Ternary gas mixtures, utilize two attaching gases, C2F6 and CF4, and are used in the optimization process for repetitive switching in an inductive energy storage system. The last type of gas mixture contains argon as a buffer gas with the Penning admixture C2H2, which increases the ionization efficiency of the gas mixture. Recommendations are made for a repetitive switch for inductive energy storage, a closing switch, and an opening switch.
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    Selection criteria for insulator materials in high-current arc environments
    (Texas Tech University, 1987-12) Engel, Thomas G.
    Insulator materials that are used in surface discharge switches or rail accelerators are subjected to the intense heat and chemistry of the arc plasma and must maintain their mechanical and electrical properties in order for the device to be dependable. The selection criteria for insulators used in these applications are presented. These criteria reflect an expected level of insulator performance and their usefulness in the selection of candidate insulator materials is determined by comparing the expected and the experimental performances of a given group of ceramic insulators. They are shown to be inadequate means of predicting the performance of the ceramic insulators considered here. The ceramics that were chosen include A12O3—SiC (alumina with 25% silicon carbide whisker reinforcement), CZA 500 (alumina and zirconia composite), MTF (aluminum titanate), Si3N4 (silicon nitride), TTZ (zirconia stabilized with magnesium oxide), and ZDY (zirconia stabilized with yttrium oxide). These materials were tested in a surface discharge switch (-300 kA, 20 fis pulse) using atmospheric air and nitrogen as discharge gases. EDX (Energy Dispersive X-ray) surface analysis is performed on the A12O3O-3—SiC, CZA 500, and MTF to determine the surface contaminants present and the possible failure modes that are caused by such contaminants. The temperature increase on the insulator's surface is assumed proportional to the I R heating in the arc discharge, and the temperature scaling, as a function of the arc current and arc resistance, is discussed. Methods to improve insulator performance in high current arc environments are also discussed.
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    The effects of electrode divergence angle and mean gap velocity on the performance of gas-blown spark gap switches
    (Texas Tech University, 1984-08) Borger, Mark Alan
    The effects of fluid velocity and electrode divergence angle on the performance of a gas-blown spark gap switch operating in a self-breakdown mode are presented. The switch was contained in a two-dimensional, axially blown, diverging wind tunnel with an aspect ratio of 40:1. The mean gap velocities, the mean flow velocities in the plane of the minimum separation point, ranged from 4 to 17 m/s. The divergence angles studied were 5.0, 7.5, and 10.0 degrees. The flushing gas used was instrument grade dry air ( < 10 ppm H20 ), and the electrode material was 304 stainless steel. High-speed interferograms were used to verify the data reduction program and to identify all events. The relationship between the minimum mean gap velocity, Ūth, and divergence angle, 0, required for a predetermined failure rate was determined in this study. This relationship is of the form, Ūth = A*e-(b0)+B, which illustrates the importance of the divergence angle on the flow rate required for successful switch operation.
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    The effects of mass flow rate and electrode divergence angle on the performance of gas-blown spark gap switches
    (Texas Tech University, 1984-05) Clarke, James Richard
    The effects of mass flow rate and electrode divergence angle on the performance of a gas-blown spark gap switch operated in the self-breakdown repetitive mode are presented. The switch was flushed with a two-dimensional, laminar flow directed between a diverging pair of electrodes. Voltage versus t i a e data were obtained for two average flow velocities, based on the flow area at the point of minimum electrode separation, of 4.1 and 8.2 m/s. The two divergence angles used were 5 and 10 degrees, and the minimum electrode separation distance was 2.54 ma. High-speed interferograms showing density variations in the gas were obtained and linked with the voltage data in order to identify various types of breakdown events and to develop both qualitative and quantitative definitions for use in the reduction of the data. From the analysis of the data, it was determined that an increase in either the mass flow rate or the electrode divergence angle improved switch performance by reducing the percentage of switch closures which were considered failures.