In my thesis, I examine whether a coupled analysis of a 3D transformer model with an external circuit is suitable for addressing unbalanced loads in a three-phase transformer. The work presents comparisons between test results conducted on an actual transformer and those obtained through the analysis of a 3D transformer model using Ansys Maxwell 3D software. The analyses are carried out in the software using a coupled AC finite element method (FEM) analysis and an external electrical circuit. The thesis begins with the creation of 3D models, specifically for 3- and 5-legged transformers, to compare results with existing real transformer data. The goal during modelling was to achieve a universal model that can be adapted to various transformer dimensions and load conditions. Subsequently, I perform measurements and analyses on the three-legged transformer, focusing on its no-load and short-circuit characteristics as well as measurements of zero-sequence impedances. For a more comprehensive comparison, I also determine the elements of the transformer's equivalent circuit using both measurements and analysis. In Chapter 5, I extend the study to unbalanced loads on a five-legged transformer with different winding connections. I analyse how various winding configurations affect the values of zero-sequence impedances in this transformer design. Through the comparisons, I find that the accuracy of the analysis results in relation to measurements depends primarily on the selected magnetization curve. Additionally, in cases where most of the in-phase magnetic field is compensated and the zero-sequence reactance is small, the resistance of the windings themselves plays a significant role.
|
