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A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Sclenice in Engineering February 20th, 1998 / All available model used to determine the 50% breakdown voltage for rod-type ami conductor-type gaps subject to switching is impulse wave forms has been applied to a tower-conductor window gap configurution. The results for rod-plane, conductor-piane and tower-conductor window gaps have all been compared and correspond well with practical data. III order to app(v the model, a charge simulation technique has been adopted ill conjunction with the 'Coulomb 3D' charge simulation package. Additional tests have been performed where parameters of'the charge simulation method am! the electrode geometl:p hare been adjusted and consequent conclusions made. Recommendations for further application of tile model have been suggested. / MT2017

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 92-94). Also available via the Internet.

dissertatic,11 submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering, I.: Johannesburg, 1998 / Corona stabilisation is not a well understood phenomenon, consequently a rigorous theoretical description of how the merhanism operates does not exist. Furthermore, postulates on the prcJ'.tse physical processes that occur during corona stabilised breakdown are varied and conflicting. 1t was thus essential to develop a qualitative theory of how the mechanism operates around which a quantitative model could be constructed. To this aim, a detailed analysis of available modelling methods and empirical data from published works was carried out. This analysis together with additional finite elements modelling done as part of this work, leads to a proposed qualitative model which serves as a basis for a quantitative model developed to simulate corona stabilized breakdown from a fixed panicle defect. There is a favorable comparison between the predictions of the model and published measurements, thus imbuing optimism in the proposed method. The problem of measuring t: .;true charge deployed in a discharge is discussed and an experiment is designed to circumvent this problem.

In this work, we have investigated numerical techniques to determine the breakdown behavior of complex semiconductor devices using two-dimensional simulation. In particular, we have augmented the device simulator SEPSIP with a capability for handling single and multiple floating field rings, and for handling devices with slanted edges. We have furthermore improved the grid width selection algorithm in SEPSIP. A capability for plotting equi-field contours was added to the code. Finally, all system dependencies were removed from the SEPSIP code, and a new version of SEPSIP (Version 2.0) was generated which can be executed on any PC/XT, PC/AT, or PC/386 compatible computer. This eliminates the need for transfering files back and forth between the PC, which had formerly been used as an I/O processor, and the VAX, which was used for numerically intensive computations. It also makes the code more accessible to scientists and engineers who are working in this important research area.

The state-of-the-art in high voltage and high energy density capacitors is dominated by biaxially oriented polypropylene (BOPP), a linear dielectric with electronic polarizability but low dielectric constant (2.2). BOPP provides an energy density of 5 J/cm3 at the breakdown, which occurs at 720 MV/m for films 10 micrometer thick. While there are many approaches to increase the energy, they either offer solutions to specific applications or suffer from fundamental limitations. The principal focus of the dissertation will be centered on rational design for the development of such materials. We study all three verticals of dielectric properties, namely: dielectric permittivity; dielectric loss; and breakdown strength. We then use the information obtained to design a copolymer with enhanced dielectric properties. We start by using simulations and experiments to delineate the mechanism by which the addition of a small number of polar --OH groups to a nonpolar polymer increases the static relative permittivity (or dielectric constant) by a factor of 2. However, the dielectric loss in the frequency regime of interest to power electronics is less than 1%. We observe that a small amount of adsorbed water plays a critical role in this attenuated loss. Further, we study the effect of other polar pendant groups on dielectric properties of polyethylene. By systematically comparing the static relative permittivity of crystalline and semi-crystalline samples we find amorphous phase as the dominant player in these types of material. The constraints provided by the surrounding chains significantly impede dipolar relaxations in the crystalline regions, whereas amorphous chains must sample all configurations to attain their fully isotropic spatial distributions. We also explore the use of the time--temperature superposition (tTS) principle for calculating the dielectric loss of the dielectric materials. This approach helps us explore time scales in simulations which were previously inaccessible using classical MD. We find that the tTS method performed well in determining dielectric losses in the system as long as unrelaxed components are not included in the calculation. This methodology, which provides us with a significantly faster and reliable pathway for calculation of dielectric loss, allows us to identify the role of polar sidegroups on the dielectric loss of common non-polar polymeric dielectrics. Further, we explore the dielectric breakdown mechanism in polymer dielectrics by introducing external electric fields in the materials. Conventionally the prediction of dielectric strength has focused on ground state energy calculation, thus restricting the analysis of the breakdown process to purely electronic in nature. While this provides reasonable predictions for low-temperature systems, we observe that electromechanical breakdown plays a crucial role in the high-temperature regimes. Our simulation results suggest that fracture mechanics drive electromechanical breakdown, which dominates over electronic breakdown at relevant operating temperatures.  Finally, we utilized these fundamental insights into dielectric properties for designing copolymer with enhanced dielectric properties.

Melvin A. Herlin [and] Sanborn C. Brown. / "July 30, 1948." / Includes bibliographical references. / Army Signal Corps No. W-36-039 sc 32037.

M.A. Herlin and S.C. Brown. / "June 14, 1948." / Includes bibliographical references. / Army Signal Corps Contract W-36-039 sc-32037.