Computation of Electro-Magnetic Transients on Three-Phase Transmission Lines with Corona and Frequency Dependent Parameters

The paper presents the calculation of electromagnetic transients (EMT) on three-phase transmission lines with frequency dependent parameters and corona, the latter represented by the model of Ref. [1]. The transmission line is divided into segments, each with a small travel delay, a longitudinal block for the modelling of frequency dependence, and a transversal model of the nonlinear effect of corona. Longitudinal "shaping" is obtained by parallel R,L elements corresponding to a series of such blocks obtained by fitting the modal line impedances over a wide range of frequencies. The computations are performed in the modal domain for longitudinal phenomena and in the phase domain for the transversal branches which include corona in each phase. The travel delay effectively decouples the nodes and the calculations for the corona branches. Thus it permits the representation of the line by Norton equivalents at its ends, so that the model can be included in a general purpose Electro-Magnetic Transients Program (EMTP). The computational results presented in the paper show wave shapes similar to those observed in measurements [13] and clearly demonstrate the significance of modelling both frequency dependence and corona.