Finite Element Analysis of Transformer Clamping Structure to Study Effect of Copper Shield on Structural Losses and Winding Eddy Losses

The losses due to transformer leakage field comprise a small percentage of the power in a transformer. Yet these losses produce localized heating which can compromise its operation. The stray field strength increases rapidly with growing rating. The stray flux intruding into the structural parts gives rise to eddy currents in them. The resulting eddy current losses may be considerable, thereby increasing the load loss of transformer [1, 5]. The objective of this work is to calculate stray losses in magnetic structures of 400 MVA 1-phase, 500–230 kV auto transformer and study the effect of copper shield on structural losses and winding eddy losses, using commercial software package Magnet (Infolytica Corp.) based on finite element method (FEM). Due to presence of non linear magnetic materials, the sinusoidal source with 60 Hz frequency induces non-sinusoidally varying magnetic fields. A transient solution (which calculates time varying magnetic field) is required for calculating fields in non-linear materials. However, this requires more computational resources. Therefore Time harmonic solution (which calculates field at 60 Hz frequency) with linear magnetic materials is used for this analyses. Further, 3D time harmonic analysis has been done to analyze the effect of varying Cu shield thickness on loss density and finally its effect on winding eddy losses has been investigated.