Síntese de funções racionais para estudos de transitórios envolvendo linhas de transmissão.

Abstract

In order to accurately represent a transmission line in programmes such as the EMTP (Electromagnetic Transients Program), it is necessary to take into account the frequency-dependence of its parameters. In such programmes, multiphase lines are first decoupled through modal transformation matrices and each mode is subsequently analysed as a single-phase line. In frequency-domain a transmission line is perfectly defined by its characteristic admittance Yc(co) and the propagation constant A(co). In this work, an overview of overhead frequency-dependent transmission line models is presented. Different methods are proposed to fit rational functions to Yc{ca) and A(ca). Both z-domain and s-domain approaches are considered. Z-domain fitting is shown to be effective when obtaining approximations to the transfer function of RLC circuits and to the propagation constant A(co). When fitting rational functions to YC(OJ) , the success o f the z-domain formulation proved to be dependent on the range of frequency considered. It is also shown that any optimization procedure should fit phase and magnitude simultaneously so as to ensure better results. The presented techniques can also be applied to the development o f frequency-dependent network equivalents (FDNE) and the design o f passive filters.