Preliminary Investigations on Propagation of Partial Discharge Induced Currents in a Transformer Winding

Historically, different variants of the distributed circuit model have been used to model the windings for the frequencies encountered in a PD excitation. However, all circuit based methodologies assume a transverse electro-magnetic (TEM) mode of propagation, and for a high frequency excitation as encountered in a PD, other modes could be excited. Therefore, deviating from the conventional circuit based methodologies, this paper employs a full-wave electromagnetic scheme for modelling of coils. Instabilities in the marching-on in time (MOT) methodologies encountered in a previous work are dealt by adopting a superior marching-on in degree (MOD) scheme. A layer winding is modelled and current distribution is obtained numerically when it is excited by a voltage source representing PD induced voltage. The currents are used to evaluate electric fields in the radial and azimuthal directions to show the existence of a non-TEM mode. The currents at the location of the voltage source and the coil terminal are compared in time and frequency domains and differences in terms of rise-times of the current pulses and the magnitude of high frequency components are elucidated.