Modelling Transformer Core with Appropriate Boundary Conditions for Partial Discharge Studies

Abstract

It is known that the ladder network and the distributed circuit models that are extensively employed for modelling the transformer windings for propagation of lightning and switching impulses are not valid for Partial Discharge (PD) excitation. The frequency contents of the PD necessitates a finer discretization of the winding which is offered by the multi-conductor transmission line (MTL) model. It has also been pointed out in recent literature concerning the analytical modelling of transformer windings for PD induced currents that the effect for core could be ignored. While this assumption is valid for the upper frequency content of the PD pulse where the flux is localized, the core still needs to be modelled in the lower frequencies. In this paper, the MTL model will be adopted for modelling the transformer winding, and a combination of current and charge simulation methods will be adopted to model the core. The accuracy of the charge simulation method for the core modelling will be shown in terms of the scalar potential of the grounded core. The difference between the responses of the transformer winding obtained with and without modelling the core will be elucidated in time and frequency domains.