Measurements show need for transformer core joint details in finite element modelling of GIC and DC effects

Abstract

Purpose This paper aims to improve the finite element modelling of transformers subjected to DC excitation, by including core joint details. Design/methodology/approach Geomagnetically induced currents (GICs) or leakage DC can cause part-cycle, half wave saturation of a power transformer’s core. Practical measurements and finite element matrix (FEM) simulation were carried out using three laboratory-scale, untanked single-phase four limb transformers resembling real power transformers in terms of the core steel and parallel winding assemblies. “Equivalent air gaps” at the joints, based on AC measurements, were applied to the FEM models for simultaneous AC and DC excitation. Findings Measurements confirm that introducing equivalent air gaps at the joints improves the FEM simulation of transformers carrying DC. Research limitations/implications The FEM simulations based on the laboratory transformers are exemplary, showing the difference between modelling core joints as solid or including equivalent air gaps. They show that, for more representative results, laboratory transformers used for research should have mitred core joints (like power transformers). Originality/value This research shows why joint details are important in FEM models for analysing transformer core saturation in the presence of DC/GICs. Extending this, other core structures of power transformers with mitred joints should improve the understanding of the leakage flux during half-wave saturation.

Toward a simple topological model of a three-phase transformer including deep saturation conditions

“…Since the models developed in this paper are intended to be used in transient network simulators, it seems appropriate to create them in the form of electrical equivalent schemes instead of using notoriously slow finite-element models (Bíró et al , 2008; Chisepo et al , 2018). The modeling approach developed in this study is based on the known topological models of Martínez et al (2005), Chiesa et al (2010) and Zirka et al (2018).…”