Influence of tap windings on the magnetic force performance of transformers

What is it about?

Knowledge of the electromagnetic forces at different winding topology provides a good basis for designers and researchers with which to deal with some of the demands that exist for the next generation transformers. Location of the regulating coil in transformer determines to effect of the electrodynamic forces on the operational behavior of the transformer. This paper presents design principles of the regulating coil in transformers and shows the electrodynamics forces by comparing the analytical results with Finite Element Method (FEM) analysis results. In this paper, electrodynamics and leakage field of magnetic force of the 25 MVA power transformers were analyzed under short-circuit condition of the high voltage windings.

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Why is it important?

This paper presents comprehensive forces analysis of 25 MV A power transformer with tap windings under short-circuit condition. By changing the location of the regulating coil three different conditions which are: +15% top, -15% middle and -15% upper tapping position of HV windings are composed. And all tapping conditions are analyzed by using MAXWELL ® based on the FEM which is a powerful tool on the estimation of the forces with in transformers. The analysis results are also validated by using approximate calculation method. The insertion of tap sections in the windings, which produces asymmetries between LV and HV windings, causes to increase in the radial and axial forces that damage to transformers. Total deformation depends on tap position. These forces shifts the windings towards to axial and radial side of the cooling gap (L1). Furthermore, it is realized that, to insert a tap section on the upper side of the coil causes more increase in forces acting on the windings according to middle of the coil. The method of calculation offers a reference to the design stage of the transformer.