Influence of Core's window height on leakage reactance of power transformers

To examine leakage reactance, different analytical methods are often used. This paper addresses one of the major problems which is practically encountered during the leakage reactance evaluation. The selection of the core's window height is also an essential factor for the leakage reactance calculation that should be carefully considered during the manufacturing of the transformer. The window's height of the core is not considered in the analytical methods yet, which results in the difference between the experimental and analytical methods, affecting the transformer's overall design. This paper presents six different three-dimensional (3-D) finite element transformer models for calculating leakage reactance under the various heights of the window. The influence of the height of the window is revealed, this effect is never considered in analytical techniques. To examine the finite element method precision, two 0.25 MVA transformer prototypes were manufactured with different heights of cores, and the same windings were used for both prototypes. The highest leakage reactance was obtained in the transformer, where the window height was minimum. On the contrary, leakage reactance decreased significantly with the increase in the core's window height.