Two-dimensional finite element modelling of overlap joints in transformer cores

The influence of overlap joints in transformer cores on the local flux and eddy current distribution and on overall transformer characteristics is studied by means of two-dimensional finite element (2D FE) models. A simplified 2D FE model of a single overlap joint is used for estimating the resulting increased magnetomotive force and increased eddy current losses. Both effects can be accounted for in a 2D FE model of the complete transformer by locally adopting modified material characteristics (viz. BH-curve and electrical conductivity) in the cross-section of the core. This novel method is demonstrated and validated by applying it to a three phase transformer The calculated no-load currents and losses are compared to the measured ones.