Scattering-theory-based methodology for electromagnetic transient analysis of nonuniform frequency-dependent transmission line structures

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Gunawardana, Manuja
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Overhead transmission lines are a vital component in electrical power networks. Overvoltage transients that originate in transmission lines due to disturbances such as lightning or switching can reach other components in a power system and create electrical insulation breakdown and equipment failure if countermeasures are not sufficiently taken. Therefore, accurate electromagnetic transient (EMT) modelling of the transmission line network is an essential requirement in designing and analyzing a power system. The increasing demand for electrical power and limited availability of land has caused overhead power transmission lines to be constructed in close proximity to each other. These close encounters such as nonparallel lines in close proximity, ultra-high voltage (UHV) lines crossing above lower voltage lines, communication lines or buried pipelines, and discontinuities such as lines undergoing sharp bends are generally nonuniform in nature. Several researchers have shown that the transient behaviour of transmission lines with such nonuniformities is far from what is predicted using conventional transmission line models that assume a uniform cross-sectional structure. Although three dimensional full-wave techniques can be used to accurately analyze these non-uniform structures, they are often associated with high computational costs and typically require iterative methods to obtain solutions. This makes them hardly suitable for circuit-type time-domain simulations. This research is focused on developing computationally efficient and EMT-simulator compatible time-domain models to analyze the transient behavior of nonuniform transmission problems involving nonparallel conductors. Transient models for both overhead and buried nonuniform structures have been derived and successfully implemented on an EMT simulator (PSCAD/EMTDC). Higher computational efficiency has been achieved by developing closed-form mathematical models which can be solved using lesser number of computations than full-wave models as well as by using parallel computing techniques. Results have been compared with those obtained using full-wave solvers and field measurement obtained by other researchers available in the literature.
Transmission Line Theory, Nonuniform Transmission Lines, Parallel Computing, Time-domain Transients