Analysis of electromagnetic force for medium frequency transformer with interleaved windings

Abstract

Medium frequency transformers (MFTs) have achieved extensive attention since they are widely used in medium frequency energy conversion systems. Different from traditional power transformer, MFTs require special consideration of short-circuit design due to their complex fault conditions. In this study, the electromagnetic forces exerted on the windings of a 1.5 kV, 35 kW, 1 kHz MFT are investigated. A working circuit model of this MFT is set up to simulate the inrush current and short-circuit current under different fault conditions. Three-dimensional (3D) transient coupled field-circuit finite element model of this MFT is developed to study the axial and radial forces exerted on the windings. The high voltage (HV) and low voltage (LV) windings are modelled into 20 and 16 sections, respectively. Then the developed axial and radial forces exerted on the HV and LV windings under inrush current and short-circuit current are compared. Furthermore, the electromagnetic forces of two kinds of interleaved windings are evaluated. The results show that suitable interleaved winding design can reduce the electromagnetic force under short circuit. The proposed approach and analysis results in this study are essential and important for MFT short-circuit design improvement, especially interleaved windings are adopted.