| Summary: | Computer simulations with programs such as the EMTP are widely accepted for lightning
transient studies, to design the system in such a way that equipment failures and transmission
line outages are prevented. In these studies, an accurate representation of the
transmission lines and towers is required. Two new and improved time-domain models for
the representation of these components are presented in this thesis. They are the frequency-
dependent and the exponential transmission line models. The former is based on synthesizing
the line functions directly in phase co-ordinates, and is used to represent
multiphase transmission lines, while the latter is a single-phase model, which also synthesizes
the line functions, to be used for tower representations. These models are valid for
the required frequency range of 1 Hz to 1 MHz. They can be used for lightning studies as
well as for many other types of transient studies. Extensive time-domain simulations have
been performed to compare the results with those produced by existing line models. The results
indicate that the new models are more accurate than some of the existing models, and
numerically stable.
Simulations of typical lightning surges have also been performed to compare the solutions
produced by the developed models with actual measurements. With these new models,
simulations match field recorded transient waveforms very well.
In addition, a simple, fast and accurate method based on the Newton-Raphson iteration
technique is introduced for finding transmission line modal parameters. It overcomes the eigenvector
and eigenvalue switching problems experienced by most other methods. With a
proper constraint equation for scaling the eigenvectors, this proposed method produces
modal parameters which can reasonably be fitted with rational functions of minimum-phase
type. With this, the modal transmission line modelling can be improved. The routine is
very stable and can be used to diagonalize the Y Z product for uncommon lines with strong
asymmetry. It has also been used to obtain the phase-domain parameters for the new frequency-
dependent line model. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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