Effect of Multiple Transposition Structures of Transformer Helical Low Voltage Winding on the Electromagnetic Force Distribution

The failure rate of power transformers due to the external short circuit fault is high. The structure of the transformer is complex, and the structural scale spans from macroscopic to mesoscopic. Most of the winding deformation accidents are microscopic structural deformations. The typical microscopic structural, transposition structure, widely exists in the helical windings wound by multiple continuous transposed conductor cables (CTC cables) in parallel. The position change of the CTC cables during the transposition process causes the asymmetry of the structure. The overall magnetic field distribution of the winding is affected, and then the electromagnetic force distribution changes. In this paper, two typical 110 kV transformers with a large number and high failure rate in the power grid are selected. Three-dimensional finite element method (FEM) models of the transformers considering the winding transposition structure are constructed. The electromagnetic force distribution of two typical 110 kV transformer low-voltage (LV) windings are obtained. The results show that due to the existence of the transposition structure, the electromagnetic force distribution of the LV windings is greatly distorted. The more the number of transposition structures, the more local maximum and minimum values appear in the electromagnetic force distribution. The research results help to improve the short-circuit resistance of windings with transposition structure.