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Reference: ISH2015_141

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Finite Element Analysis Model for Failure Analysis of Epoxy-Bonded Continuously Transposed Cable



Power transformer windings usually are made from continuously transposed cable (CTC) in order to reduce eddy current losses and reach low winding cost. The main disadvantage of this kind of multiple stranded conductor is the low bending stiffness due to the slender strip cross section. In the worst case winding deformations can occur, if the transformer is exposed to high short-circuit currents. An increase in bending stiffness can be realized with epoxy-bonded CTCs: The strips are covered with an epoxy resin that melts during the factory drying process of the windings' insulation and glues the strips together. In this paper a mechanical Finite Element Analysis (FEA) based simulation model for such kind of CTCs is proposed. The aim is to investigate the increase in buckling strength resulting from the epoxy resin bonding. The underlying model is a curved CTC sector, which represents a part of one winding that is radially supported by spacers. The glued contacts areas between the copper strips are modeled using a Cohesive Zone Model approach. The underlying parameterization is derived from overlap shear and T-peel tests conducted with copper strips. The temperature stability of the epoxy bonding is verified with overlap shear tests at 20 °C. THE FEA models are loaded by a radially inwards directed force density to simulate the short circuit forces onto a winding. The load-deformation characteristic is analyzed as well as the stress distribution in the contact zones and the equivalent stress inside the copper. Simulation results show an huge increase in CTC stiffness due to the epoxy bonding: Improvements in critical buckling strength by a factor of up to 9.3 are realized for the investigated CTC geometries. The proposed simulation approach can help to validate the improvement in short circuit strength with epoxy bonded CTCs as testing is complicated, time and material-consuming.

File Size: 4,4 MB

Year: 2015

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