Stress Distribution Characteristics of Composite Wire-Paper Winding Structure under the Radial Electromagnetic Force

The buckling of transformer windings caused by radial short-circuit electromagnetic force is one of the significant causes of transformer failures, threatening the safe operation of the entire power system. Comparing the maximum stress in the windings with the critical buckling stress is an essential criterion for analyzing whether the buckling will occur. Hence, it is vitally important to obtain an accurate stress distribution in windings under radial electromagnetic force. Studies have shown that the thin paper insulation wrapped around the conductors can affect the mechanical strength of windings. Therefore, it is necessary to consider the influence of paper insulation on stress distribution in the research. In this paper, the copper-paper layered ring winding model, which can be analyzed as a 2D stress distribution problem, has been constructed. The governing equation for this model in polar coordinate has been acquired. Because of the assumed close contact, the displacement and radial stress must match at the copper-paper interface. By solving the equations, the stress distribution can be obtained. As a calculation sample, the low-voltage (LV) winding of a type of 110 kV transformer has been studied. There are two Continuously Transposed Conductors (CTCs) that wound in parallel in one disk, so the model contains two layers of copper and one layer of paper. The hoop stress distribution and the radial stress distribution have been calculated. The results show that the hoop stress varies more than 15% from the innermost radius to the outermost radius and the radial stress is small in comparison. The hoop stress in the paper layer is much smaller than that in the copper layer. The obtained results have been verified using the finite-element method.