This research is devoted to an investigation on the attractive width of high voltage transmission lines to lightning strikes. In order to design the optimal lightning protection, the estimated number of lightning flashes on the line, which is based on its attractive width, needs to be determined. The investigation was performed using experiments with model tests at the Mississippi State University High Voltage Laboratory. For laboratory experiments, a total of 2,100 negative and positive switching impulse voltages were applied to transmission line models from a conducting rod, which represented a lightning downward leader. Different tested models of transmission lines on a scale of 1:100 were used. The effects of overhead ground wires, phase conductors, tower structures, and the magnitude and polarity of lightning strokes were also studied. The attractive width increased gradually with the height of overhead ground wires and towers as well as the magnitude of the lightning stroke current. Impulse polarity had an impact on the attractive width, and the attractive width for negative polarity was larger than that for positive polarity. The taller tower had more effect on flash distribution to transmission lines than the shorter one. The experimental results agree with the actual transmission line observations published in literature. The new expressions for the attractive width of transmission lines, based on the experimental results, were established. The accurate estimation of the attractive width can help electric power utilities plan transmission systems reliably and economically. The detailed description of the background problem, proposed method, experimental results, and analysis are presented in this dissertation.

Recently there has been increasing interest in using glycerol as a substrate on steam reforming due to the increase of biodiesel production. With the increase of biodiesel production a glut of glycerol has resulted and this would be a more suitable substrate for value added production of hydrogen from reforming. Reforming biorenewable viscous fluids such as glycerol is difficult due to mass transfer limitations associated with vaporizing glycerol to gas phase before steam reforming. This study was to evaluate the feasibility of reforming electrically atomized liquid phase glycerol by means of a technique called electro-spray. It was hypothesized that reforming electrically charged glycerol nanodroplets on an oppositely charged conductive catalyst will increase the reforming performance as opposed to a neutral catalyst-substrate system. Hydrogen yield, selectivity was increased by 20%, 25% respectively when nanodroplets introduced. Exerting an electrical charge to the substrate-catalytic system significantly enhanced the reforming performance irrespective of the physical phase.

No description available.

No description available.

Electronic power devices made of silicon carbide promisesuperior performance over today's silicon devices due toinherent material properties. As a result of the material'swide band gap of 3.2eV, high thermal conductivity, itsmechanical and chemical stability and a high critical electricfield, 4H-silicon carbide devices have the potential to be usedat elevated temperatures and in harsh environments. Shortercarrier lifetimes and a reduction in the necessary width of thelow-doped drift zone in silicon carbide devices compared totheir silicon counterparts result in faster switching speedsand lower switching losses and thus in much more efficientpower devices. High-voltage 4H-silicon carbide diodes have been fabricatedin a newly developed processing sequence, using standardsilicon process equipment. Epitaxial layers grown by chemicalvapor deposition (CVD) on commercial 4H-silicon carbidesubstrates were used as starting material for both mesa-etchedepitaxial and implanted p+n-n+ planar diodes, Schottky diodesand merged pn-Schottky (MPS) diodes, together with additionaltest structures. The device metallization was optimized to givea low contact resistivity on implanted and epitaxial layers anda sufficiently high Schottky barrier with a singlemetallization scheme. Different high-field termination designshave been tested and breakdown voltages of up to 4 kV onimplanted, field-ring terminated diodes were achieved,corresponding to 80% of the critical electric field. A 5kVepitaxial diode design with a forward voltage drop of 3.5V at acurrent density of 100Acm-2 equipped with an implanted junctiontermination extension (JTE) was also fabricated. A new measurement setup was designed and built with thecapability of measuring current-voltage and capacitance-voltagecharacteristics of semiconductor devices at reverse biases upto 10kV. Together with these electrical measurements, theresults of other characterization techniques were used toidentify performance limiting defects in the fabricated siliconcarbide diodes. Increased forward voltage drop of bipolardevices during on-state operation was studied and it was shownthat the stacking faults causing forward degradation arevisible in scanning electron microscopy. With the help ofsynchrotron white-beam X-ray diffraction topographs (SWBXT),electron beam induced current (EBIC) and electroluminescencemeasurements of silicon carbide diodes, the role of screwdislocations as a dominant source of device failure in the formof localized microplasma breakdown was identified. Screwdislocations with and without open core have been found tocause a 20-80% reduction in the critical electric field of4H-silicon carbide diodes, both for low-voltage (150V) andhigh-voltage (~5kV) designs. While micropipes have almost beeneliminated from commercial silicon carbide material,closed-core screw dislocations are still abundant withdensities in the order of 10000cm-2 in state-of-the-art siliconcarbide epitaxial layers.

This report describes the development of a high-voltage connector at the request of Scandinova Systems AB in Uppsala. The development process is described from the making of a customer demand specification, to the making of drawings for the manufacturing of prototypes. Scandinova develops high-voltage modulators, hence the need for connectors that can handle very large power pulses. Their current connector has several weaknesses that may cause the connector to melt or catch fire. The development began with a number of studies that included the modulator structure and the current connector structure and functions. In addition, to collect Further demands, requests or ideas for the new product a survey were distributed to the staff at Scandinova. All the collected information was summarized in a a customer demand specification. There after a wide variety of concepts were generated. The concepts were then compared, merged, improved, or rejected in order to get a stronger concept. The remaining concepts were then evaluated using a concept selection matrix. In consultation with Scandinovas R & D department it was then decided to further develop four of the concepts in 3D CAD. The selected concepts was then designed in detail and the material selection were made. This was followed by a final evaluation with Scandinova to evaluate the concepts. The evaluation showed that three of the concepts were still interesting. Therefore, drawings were produced for the remaining three concepts, the drawings were there after submitted to Scandinova for prototyping. This report shows that at least one of the concepts seems to be substantially better than Scandinovas current high-voltage connector.

Multilayer ceramic capacitors (MLCCs) are typically manufactured as follows: First, stirring and mixing dielectric ceramic powders with a binder and a dispersion agent in a ball mill for several hours to prepare slurry having a desired viscosity. Next, a green sheet is prepared by a doctor blade method, wherein, the slurry is discharged onto a carrier film through a small orifice and the carrier film is pulled under a doctor blade or a slot die, which is set at a particular height to obtain a desired sheet thickness. The sheet is then dried to produce the green sheet. Then, a conductive paste is applied on a number of green sheets to form internal electrodes by screen-printing. The desired number of ceramic green sheets with internal electrodes are stacked and compressed to form a laminated body. The laminated body is then diced into a number of capacitor elements having a predetermined size. Thereafter the capacitor elements are through binder burnout and sintered then finally external electrodes are formed on opposite end portions of each of the capacitor elements to produce multiplayer ceramic capacitors. Once terminated, MLCC is typically electro-plated with a layer of nickel followed by a layer of tin in order to be surface-mountable. Surface mounting is soldering of components onto PCBs. The nickel layer is typically referred to as the barrier layer. Although nickel is solderable, it does not readily dissolve in molten solder as silver does. The end terminals when the capacitors are soldered to PCBs. Tin coatings serve to protect the nickel from oxidation and to make components readily solderable. Precious metal electrode (PME) system and solvent base are introduced in this report. Capacitors were fabricated from 22£gm thick tapes consisting of ceramic powders (X7R AD292U, Degussa Corporation and NP0 VLF-220, MRA Laboratories, Inc.) that involves a sequence of a large number of processing steps, with production losses associated with each step. Optimized and controlled processing parameters can get reliable yield.

<p>Electronic power devices made of silicon carbide promisesuperior performance over today's silicon devices due toinherent material properties. As a result of the material'swide band gap of 3.2eV, high thermal conductivity, itsmechanical and chemical stability and a high critical electricfield, 4H-silicon carbide devices have the potential to be usedat elevated temperatures and in harsh environments. Shortercarrier lifetimes and a reduction in the necessary width of thelow-doped drift zone in silicon carbide devices compared totheir silicon counterparts result in faster switching speedsand lower switching losses and thus in much more efficientpower devices.</p><p>High-voltage 4H-silicon carbide diodes have been fabricatedin a newly developed processing sequence, using standardsilicon process equipment. Epitaxial layers grown by chemicalvapor deposition (CVD) on commercial 4H-silicon carbidesubstrates were used as starting material for both mesa-etchedepitaxial and implanted p+n-n+ planar diodes, Schottky diodesand merged pn-Schottky (MPS) diodes, together with additionaltest structures. The device metallization was optimized to givea low contact resistivity on implanted and epitaxial layers anda sufficiently high Schottky barrier with a singlemetallization scheme. Different high-field termination designshave been tested and breakdown voltages of up to 4 kV onimplanted, field-ring terminated diodes were achieved,corresponding to 80% of the critical electric field. A 5kVepitaxial diode design with a forward voltage drop of 3.5V at acurrent density of 100Acm-2 equipped with an implanted junctiontermination extension (JTE) was also fabricated.</p><p>A new measurement setup was designed and built with thecapability of measuring current-voltage and capacitance-voltagecharacteristics of semiconductor devices at reverse biases upto 10kV. Together with these electrical measurements, theresults of other characterization techniques were used toidentify performance limiting defects in the fabricated siliconcarbide diodes. Increased forward voltage drop of bipolardevices during on-state operation was studied and it was shownthat the stacking faults causing forward degradation arevisible in scanning electron microscopy. With the help ofsynchrotron white-beam X-ray diffraction topographs (SWBXT),electron beam induced current (EBIC) and electroluminescencemeasurements of silicon carbide diodes, the role of screwdislocations as a dominant source of device failure in the formof localized microplasma breakdown was identified. Screwdislocations with and without open core have been found tocause a 20-80% reduction in the critical electric field of4H-silicon carbide diodes, both for low-voltage (150V) andhigh-voltage (~5kV) designs. While micropipes have almost beeneliminated from commercial silicon carbide material,closed-core screw dislocations are still abundant withdensities in the order of 10000cm-2 in state-of-the-art siliconcarbide epitaxial layers.</p>

Owing to their inherent isolation and ability for remote interrogation, wireless sensors are an effective way to monitor the operation of high-voltage power transmission lines. A wireless sensor on a high-voltage line has the potential to form corona discharges, particularly on an exposed antenna. The effects of corona formation on the antenna of a wireless radio frequency (RF) communication system were studied. The physics of corona plasma formation and charge composition was analyzed, leading to a theoretical understanding of corona interaction with the antenna. Through a series of high-voltage experiments, the effects of corona on the impedance and gain of an antenna, as well as the RF interference generated by corona current pulses, were identified. RF interference and low-frequency corona current were observed to have the largest impact on a wireless RF system. Corona was found to have no significant impact on the impedance or gain of an antenna. Based on the results, design guidelines were proposed for an antenna and RF front end to be used in wireless high-voltage sensing applications.

No description available.