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UBC Theses and Dissertations

Voltage and current profiles and low-order approximation of frequency-dependent transmission line parameters Marti, Luis


In this thesis project, two models related to the simulation of electromagnetic transients in power systems, have been developed. The first model has been designed to find voltages and currents at a number of intermediate, equally spaced points along the line ("profile"), from the solution at the end points (taking into account the frequency dependence of the line parameters). This "profile model" is derived from the cascade connection of n equivalent circuits, each one representing a segment of the line. The solution is carried out with an internal time step which is an exact submultiple of the travel time of the propagation mode in consideration. A series of tests shows that the results obtained with this model are more accurate than those obtained if the standard practice of segmenting the line is followed. With the aid of the profile routines, a movie which illustrates the propagation of transients along a line, has been produced as well. The second part of this thesis describes the development of a low-order approximation of the frequency-dependence of line parameters, from a reduced amount of information. Using the electrical parameters at power frequency and dc conductor resistances, the tower configuration of the line is reconstructed. This equivalent line configuration permits the evaluation of the line parameters over a wide frequency range. Rational functions are then used to approximate the frequency-dependence of these parameters over a limited frequency range with a reduced order model. Analytical tests and transient simulations, indicate that the model is reasonably accurate over the frequency range of interest in most practical applications. Both models have been incorporated into the UBC version of the Electromagnetic Transients Program (EMTP).

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