Thesis (Ph. D.)--University of Wisconsin--Madison, 1985. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

D.Ing. (Mechanical Engineering) / This research proposed to develop a mathematical model for the prediction of aeolian vibration levels on overhead transmission lines in order to be able to ensure that damping systems are designed optimally in future. In order to enhance the understanding of aeolian and wake-induced vibration further, it also proposed to implement and apply the fluid flow simulation technique of Computational Fluid Dynamics (CFD) to both single conductors and conductor bundles. The Introduction of the CFD tool to the field of transmission line vibration, will ensure that bundles could be optimally designed for future applications. Wind-induced vibrations are known to cause expensive damage to the conductors and related hardware through fatigue or clashing of the bundled conductors. The primary cause of conductor aeolian vibration is the alternate shedding of wind-induced eddies from the top and bottom sides of the conductor, whereas wake-induced oscillations is peculiar to bundled conductors and arises from effects of the shielding of leeward conductors in bundles by windward ones. In order to study the phenomenon of aeolian vibration, research was undertaken utilising a full scale transmission line test station close to Kroonstad in the Orange Free State. Commercially available computer based packages were used for the development and simulation of both the mathematical model and fluid flow. During the flow simulations, an actual Zebra conductor and Zebra bundle configuration were utilised. For the development of the mathematical model, the pratical results, as measured at the Kroonstad transmission line test station during Phase I, were utilised. From the tests performed during Phase I, it was concluded that the damping solutions, currently used by Eskom as tested during Phase I, are all effective in controlling the aeolian vibration. The Stockbridge damper proved to be avery effective damper. Two models for the prediction of aeolian vibration levels were derived. Results showed that the vibration levels could be estimated to the correct order of magnitude and in many cases the precise values. The accuracy of the model was further improved by the inclusion of the Strouhal number as a function of windspeed. It has been decided by the author 10 develop and design a low cost vibration activity indicator for aeolian vibration measurements. The T-R-I-V-A-I has shown that it is a repeatable, reliable device, Ideally suited for line vibration detection. A new device, the W-I-V-I, has also been designed and implemented by the author for the detection and quantification of wake-induced vibration. During the simulation of the flows around a conductor in the steady state, it was established that the flow around as smooth cylinder and a Zebra conductor, is very similar, however, it was established that the rough outer surface of the Zebra conductor acts as a vortex generator. It has been found that a stability relationship exists between the degree of symmetry of the pressure cell, directly in front of the leeward conductor and the wake-induced vibration. Results for the unsteady flow situation showed the initiation and dispersion of the vortices as they are generated alongside the conductor. It is recommended that the developed model's accuracy be further enhanced. It should be established if .there are families of curves and data that belong together and that contribute to the amount of scatter in the parameters measured such as vibration amplitude, Strouhal number, etc. The applicability of CFD to the transmission line field should be enhanced, with the view of increasing bundle performance, both from an electrical and mechanical point of view.

M.Ing.(Electrical and Electronic Engineering) / In the ideal communication system no noise is present and no errors will be made. However, in practice, communication is over noisy channels which cause errors in the information. There is thus a necessity for the control of these errors. Furthermore, several channels impose runlength or disparity constraints on the bit stream. Until recently, the error control on these channels was applied separately to imposing the input restrictions with constrained codes. Such a system leads to poor performance under certain conditions. and is more complex and expensive to apply than systems where the error control is an integral part of the constrained code or decoder. In this study, we firstly investigate the error multiplication phenomena of constrained codes. An algorithm is presented that minimizes the error propagation probabilities of memoryless decoders according to two criteria. Another algorithm is presented along with the first to calculate the resulting bit error probabilities. The second approach to the error control of constrained codes is the construction of combined error-correcting constrained finite-state machine codes. We investigate the known construction techniques and construct several new codes using extensions of the known techniques. These codes complement or improve on the known error-correcting constrained codes with regards to either complexity, rate or error-correcting capability. Furthermore, these codes have good error behaviour and favourable power spectral densities.

With the increasing market demand for wideband multifunctional electronic systems, real-time broadband measurement systems with few picoseconds switching rates are essential. Furthermore, stable millimeter wave sources are required to drive these wideband electronic systems. Nonlinear transmission lines (NLTLs) are high impedance transmission lines periodically loaded with reverse biased diode serving as varactors. Extremely high bandwidths are achievable because of the possibility to fabricate these structures monolithically, which is why pulses with ultra short transitions can be generated using NLTLs. Also, efficient wideband frequency conversion is made possible by NLTL technology. / In this thesis, a comprehensive study of NLTLs and their applications is presented. Sharpening of the edges of electrical pulses, voltage dependent true time delay, and harmonic generation in NLTLs are investigated through analytical studies as well as circuit simulations and experimental measurements. Designing the best possible mixers, frequency doublers, and edge sharpeners and optimizing them are not the objects of this thesis. The main objective is to study an alternative design approach by using NLTLs. To this end, analytical solution for the magnitude of the third harmonic along a nonlinear transmission line is derived for the first time. Also, for the first time the lowpass nature of the NLTL is combined with the solutions for the magnitudes of harmonics in order to improve the validity range of the predicted harmonics. An NLTL harmonic generator is fabricated and measurement results are reported. / Inspired by the distributed nature of nonlinear transmission lines, a novel filtering method is introduced for the suppression of the unwanted signals in different NLTL applications. The filtering method is applied to a nonlinear transmission line frequency multiplier in order to filter the third harmonic. The distributed filtering is also used to suppress the image signal in an NLTL mixer. The proposed filtering method is general and can be applied to other periodic structure as well (such as distributed amplifiers and distributed mixers). For implementing the filtering, compact complementary split ring resonators are proposed and designed for an NLTL frequency doubler.

Thesis (M.Eng.(Electrical Engineering))--University of Pretoria, 1999. / Includes abstract in English and Afrikaans. Includes bibliographical references.

Numerical modeling of electromagnetic fields is becoming an important topic in such diverse areas as microwave and RF engineering, antenna design, bio-electromagnetics, and electromagnetic compatibility and interference (EMC/EMI). Among several techniques, time-domain schemes are of particular interest, due to their high flexibility and ease of implementation. This thesis is focused on the Transmission Line Matrix (TLM) method, based on a space and time discrete formulation of Maxwell's equations. The objective of this thesis is to develop, implement and test a number of techniques aimed to the enhancement of the accuracy of the method without increasing the computational load. The link between the electromagnetic theory and the TLM updating equations is first investigated, creating a solid background for the implementation of hybrid schemes characterized by better accuracy. The problem of coarseness error is in particular addressed. Two methods are proposed and analyzed. In the first approach the knowledge of the relationship between field equations and TLM equations is exploited to incorporate the static field behavior in the vicinity of singularities into the three-dimensional TLM mesh. Secondly, the field distribution around a corner is represented in terms of an equivalent circuit derived from a quasi-static approximation of the Green's functions for an infinite conductive wedge. As a result, relatively coarse TLM meshes, in combination with hybrid schemes, can be used to obtain highly accurate results, within the dispersion error margin, across a wide frequency range. By taking advantage of these techniques it is possible to incorporate more information of the structure under study into the TLM solution, thus creating an accurate and efficient CAD tool. / Graduate

M.Ing. / Please refer to full text to view abstract

The use of electrical networks for telecommunications has a long history. It has been known since the beginning of the twentieth century [Ahola03]. The idea of using electrical networks for broadband communications arose in the 1990s [Hrasnica et al 04]. Recent and growing research interest has indicated that PowerLine Communications (PLC) is the threshold for achieving broadband delivery particularly in very dispersed and low teledensity areas. Currently, there are numerous PLC trials and commercial deployments underway inside and outside South Africa. Nevertheless, these PLC deployments are very isolated, done without clear methodology and performance remains bound to the physical layout of the electrical network. Because of that high bandwidth broadband PLC systems are prone to poor performance and this in turn limits the acceptance and deployment of this emerging alternative broadband technology. Though, PLC technical challenges are being addressed, there has been little analysis and research work that is focused on the “Development of Methodologies for Deploying and Implementing Local & Medium Area Broadband Power Line in Residential and Office Electric Grids” that would lead to broadband PLC being adopted and be of greater use to non-broadband communities of South Africa. PLC is a term describing several different systems using electrical grid distribution wires for simultaneous distribution of data by superimposing an analog signal [Hrasnica et al 04]. The research proposed and presented broadband PLC methodologies for typical medium voltage and local voltage PLC networks. These methodologieswere implemented and experimented with in configurations which closely mirrored residential and office settings through laboratory and multibuilding experiments using commercial 2nd Generation Mitsubishi Electric PLC technology. Research results presented not only serve to provide insight into broadband PLC but also how it handled broadband applications (communications), competed and compared with other technologies such as Ethernet LAN. In combination with networking communication theories, the research explored and analyzed the extent of PLC in providing broadband communication to residential and office electric grids at the University Fort Hare, Computer Science Department.

A digital program has been developed which uses the Monte Carlo technique to estimate the risk of failure of transmission line insulation during system switching operations. The effect of overvoltage waveshape on insulation strength is included. A simple electrical system is used to demonstrate the method and to investigate some general aspects of error and parameter sensitivity. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Ing. (Electrical Engineering Science) / In today's rapidly changing technological environment, more and more importance is being attached to producing products as small as possible to save space as well as materials. Systems today use a wide range of signals, from those used to transmit energy, to small signal electronic signals used for control purposes. As these signals are not very compatible, they must each have their own cable harness to prevent unwanted interference between the signals. As a first step to reducing system size, the control signals (or any signal containing information) may be transmitted on the power transmission line, using techniques investigated in this dissertation. Systems using the same conductors for simultaneous energy and data transmission have many applications ranging from high tech systems to low cost rural communication. Examples of systems where this technology can be applied include: (a) distributed high frequency power systems, where switching of remote equipment can be done from a central point; (b) communication and control in harsh environments such as mining complexes, where switching of fans and motors for example can be done from a central point, while a communication network can be established by placing the information signals on the power cables; and (c) flexible manufacturing cells, where robots can be controlled via the power transmission harness. On the other hand, rural communication systems can be realised over the 50 Hz utility transmission network in remote areas. Such a system has the advantage of offering a low cost solution to providing access to communication to a large number of people spread over a large area. The work described In this dissertation covers two systems, firstly information transmission over the 50 Hz utility network and secondly, the design of a high frequency distributed power system utilising simultaneous information transmission on the transmission line.The first three chapters give an introduction to the technology and discuss the theory which must be applied to make simultaneous energy and information transmission over one conductor viable. Chapter 4 discusses the 50 Hz utility network as an information distribution network. The advantages and disadvantages are discussed, while some solutions are proposed how the disadvantages can be overcome. Chapter 5 discusses a high frequency distributed power system using simultaneous information transmission. The converter design is discussed, while some special design considerations are given which are essential to successful simultaneous information transmission in such a distributed system. To help with the design of the converter used, a simulation was carried out to predict the voltage and current waveforms in such a converter, the results of which can be seen in Appendix B.. The aim of simultaneously transmitting energy and information on the same transmission line was realised in both cases. In the 50 Hz system it was shown that adding external networks to guide the information carrier around obstacles such as 50 Hz power transformers improved the information transmission. A distributed power system however does not need external elements as long as the design of transformers follows the special considerations as described in chapter 5.