Wideband modeling of transmission lines and cables

The objective of this dissertation is to develop an accurate model to simulate the response of transmission line and underground cable systems under transient conditions. The proposed model is targeted to overcome the limitations associated with the existing models in EMTP-RV software (Electromagnetic Transients Program Restructured Version).;Phase domain identification of propagation function requires the computation of modal time delays. The initial estimation of modal delays is explained and a time delay search algorithm is proposed. The search is done by direct experimentation with rational fitting with delay as a parameter.;This work also contributes to the improvement of numerical stability of frequency dependent transmission line and cable models used for electromagnetic transient analysis. Transmission devices described with rational functions are transformed into time domain with efficient convolution operations. However, recursive computation of convolution integrals creates numerical errors. The numerical errors in time domain are estimated in terms of the transfer function parameters for a given line or cable model. On the basis of this estimation a methodology based on parameter scaling using constrained least squares technique is developed for the improvement of numerical stability. The numerical advantages of the new method are supported by demonstration and comparison with existing models.;In this work, the method of traveling waves is adopted for the accurate computation of electromagnetic transients on underground cables and overhead transmission lines. Efficient solution of traveling wave equations requires the frequency domain characterization of two matrix functions: propagation and characteristic admittance. These parameters are identified directly in the phase domain as rational transfer functions. The propagation function constitutes a high order wideband system with inherent time delays. A weighted fitting technique is presented and advocated for the approximation of propagation function as a rational transfer function. The proposed fitting technique is also applicable to the identification problem of characteristic admittance. It is shown that this technique provides low order and robust approximations for transmission line and cable parameters compared to existing fitting techniques in the literature. Low order approximations provide faster simulations in the time domain.