Accurate value of transmission line parameters is important for power system protection applications, especially for distance relays whose zone settings are based on positive sequence line impedance. The research is devoted to estimating transmission line positive-sequence parameters from synchronized or unsynchronized measurements of voltage and current phasors that are obtained at both terminals of the line. The positive sequence parameters including series impedance and shunt admittance can be linearly estimated. The linear least square algorithm has been derived in this dissertation for different transmission line configurations. The algorithm is able to handle both synchronized and unsynchronized measurements and deal with potential synchronization errors by explicitly modeling the synchronization angle. Sample results are reported to demonstrate the effectiveness of the proposed method. Three types of transmission line models depending on line length (long, medium and short) are studied in this dissertation. Chapter 3 uses unsynchronized data for the long transmission line. The derived method can detect the unsynchronized angle and estimate the positive sequence of long line parameters. The proposed method is examined with negative impacts such as errors on currents and voltages data. These errors are added randomly to one set each time to test the robustness of the developed algorithm. The medium transmission line algorithm derivation is presented in chapter 4. This chapter uses a linear least square to estimate the lumped parameters of a medium transmission line. The two different transmission line circuits are used to model the medium line. The first circuit is a single transmission line with two nodes and is used to evaluate the developed algorithm. The second circuit is a double transmission line. These two lines can have the same or different line parameters or line length. The developed algorithm shows that the proposed method achieves highly accurate results for the estimation of positive sequence line parameters. The short transmission line is studied in chapter 5. The short transmission line uses less data than the long or medium lines because in this model the shunt capacitance is omitted. Thus, the linear estimation yields highly accurate results. Case studies are considered to test the robustness of this developed method. The line temperature mainly affects the series resistance, and the developed algorithms in previous three chapters can accurately estimate the transmission line parameters. To simplify the real-time estimation of line resistance and temperature, the series inductance, and shunt capacitance can be treated as constant and known values. Chapter 6 provides such studies of estimating resistance by treating inductance and capacitance as known values.

We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux.

No description available.

Terminating transmission lines at either the source or the load end with a damping resistor is frequently used to improve the signal integrity of clock or control lines on printed circuit boards. While a number of termination variants may produce similar results in regards to signal integrity, the electromagnetic compatibility performance can vary due to different current and voltage distributions along the line. This thesis investigates the impact of transmission line terminations on radiated emissions.

<p>Syftet med detta examensarbete har varit att undersöka, vidareutveckla samt ta fram nya koncept som alternativ till den befintlig lösning för styrning av kopplingshylsor i en powershift-transmission. Vidare har trender inom transmissionsmekanismer undersökts.</p><p>Arbetet har bedrivits som en förstudie med framtagande av QFD, och kravspecifikation samt konceptgenerering med utvärdering av tänkbara koncept. Funktionsanalys uppfördes som stöd till idégenereringen som bedrivits med hjälp av brainstorming, brain-writing och morfologisk metodik.</p><p>Under arbetet med QFD:n uppenbarades en problematik som kan ge upphov till skevhet med faktorer som viktas på fel systemnivå. Som exempel kan inverkan på effektförluster och motorbelastning av mekanismens kraftsystem vara en källa till skevhet.</p><p>Resultatet mynnar ut i fyra koncept för styrning och kontroll av kopplingshylsor i en power shift-transmission. Tre av koncepten baseras på borstlösa DC (BLDC) motorer med mekanisk utväxling för val och förflyttning av kopplingshylsan. Det fjärde konceptet är en välbeprövad lösning där kopplingshylsan förflyttas med hjälp av hydraulkolvar tillika skiftaxel. Samtliga koncept medger icke-sekventiella växelval för optimering av prestanda och växlingskomfort.</p><p>Genomförd förstudie kring växelmekanismer talar för att elektriska motorer kommer att ersätta mindre hydrauliska system i framtiden. Såväl forskning som miljöaspekter och allmän teknikutveckling pekar mot detta.</p><p>Rekommendationer för fortsatt arbete med projektet innefattar djupare patentsökningar, detaljkonstruktion, simulering och validering, vilka är punkter som behöver ytterligare uppmärksamhet.</p>

<p>In wireless transmissions the communication is often degraded by random fades, noise and other performance reducing phenomena. One way of improving the stability and reducing the error rates is to use relaying techniques where several nodes cooperate in a transmission between two of them. This thesis analyzes some of the available Decode-and-Forward relaying schemes for wireless transmission. The investigated schemes are conventional repetition coding, partial repetition coding and non-collaborative direct transmission. I have developed a three-node communication system using an audio channel to test the performance of repetition coding and direct transmission. This audio communication system can also be used to demonstrate some basic phenomena in wireless transmissions and how different scenarios change the performance of the communication. A theoretical performance analysis and computer simulations of the schemes performance over a Rayleigh fading channel are done as a basis for comparison. As a result we see that in the audio communication system repetition coding actually degrades the performance, compared to direct transmission, when using a relatively slow data rate in comparison to the speed of the fading in the audio channel.</p>

Natural convection provides a means for circulating fluids without the use of pumps. This type of system is of great interest for a wide variety of applications, including solar heaters, process industry, and nuclear reactors. Natural convection will play a vital role in the area of passive safety and reliability, particularly for the development of Generation IV nuclear energy systems. This study mainly focuses on the linear stability analysis of asymmetrically heated/cooled natural convection loops with large temperature variations across the heated core. The study targets the Argonne Lead Loop Facility (ALLF), a concept for an experiment loop to support the development of the Secure Transportable Autonomous Reactor-Liquid Metal (STAR-LM) at Argonne National Laboratory, using lead-bismuth eutectic (LBE) as the primary reactor coolant. A one-dimensional linear stability analysis is performed and the Nyquist criterion is employed to find the linear stability boundary of both forward and backward circulations. It was found that the natural circulations could be linearly unstable in a high Reynolds number region. Increasing loop friction makes a forward circulation more stable, but destabilizes the corresponding backward circulation under the same heating/cooling conditions. The preliminary results suggest that as the Peclet number decreases, the forward circulation is prone to become unstable while the backward circulation is prone to remain stable. / Graduation date: 2003

Heat transfer and fluid mechanical behavior of water flowing horizontally in vertically-narrow rectangular channels was studied in this work. Friction factor and Nusselt number variations were determined experimentally for four different wall heating conditions, and for aspect ratios(height to width) of 5, 4, 3, 2, and 1. Wall heating conditions examined were: all surfaces heated; three surfaces heated, the top adiabatic; one side surface heated the others adiabatic; and the bottom surface heated, the others adiabatic. Friction factors, in laminar flow, varied as predicted from analysis. The critical Reynolds number varied linearly with 1n(D[subscript]). Local Nusselt numbers were determined, at each aspect ratio and heating condition, as functions of Reynolds and Rayleigh numbers. Mixed convection was the result of buoyancy-induced secondary flows. Local Nusselt numbers decreased in a manner common to pure forced convection, reaching minimum values some distance from the entrance, then increased due to the presence of the secondary flows. For given aspect ratio, local Nusselt numbers were found to increase and the thermal entrance lengths decreased, with increasing Rayleigh numbers. In the thermal entry region, for all heating conditions except the bottom-heating case, local Nusselt number behavior showed minor dependence on aspect ratio. / Graduation date: 1999

Graduation date: 1998

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Javier Garcia-Frias, Dept. of Electrical and Computer Engineering. Includes bibliographical references.