Model of corona for an EMTP study of surge propagation along HV transmission lines

A mathematical model of the phenomenon of corona on an HV transmission line under the influence of overvoltage surges is presented. This model has been incorporated into the alternative-transient-program/electromagnetic-transients-program (ATP-EMTP) as a user-defined component, using the MODELS feature of this program. This component has been inserted as a nonlinear voltage-dependent capacitance at regular intervals along the transmission line, in order to compute the attenuation and distortion of the lightning-induced surges as they propagate along the line. The proposed model is verified thoroughly by an extensive comparison of the simulation results from the paper with direct measurements by previous authors in the course of a number of physical tests, as well as with results of simulations by other authors. It is shown in the paper that the omission of the corona phenomenon can lead to noticeable errors in the assessment of both the steepness and peak value of the surge waveform as it propagates along the line. These facts are especially relevant to the problem of insulation co-ordination on overhead lines. The model used in the paper is applied to a study of the lightning performance of 110 kV overhead lines.