Implementation of surface impedance boundary conditions in the quasi three-dimensional finite-difference simulations of generator end regions

Abstract

Predicting the distribution of the eddy currents circulating in the press plate or other end metallic components and the impacts of eddy current on the magnetic field in the end region is crucial for the design of large synchronous generators. Compared to the accurate but extremely time-consuming full three-dimensional (3D) finite-element analysis (FEA) that may take several days to complete, a new quasi-3D simulation with finite difference equations can provide acceptable solutions of the magnetic field and eddy current distributions in the generator end region within a few minutes and is thus an appropriate tool at the initial design stage. This paper proposes an approach to estimate the distribution of eddy currents in the end metallic components by implementing the surface impedance boundary conditions (SIBCs) in a quasi-3D finite-difference (FD) scheme. The effects of nonlinear material properties and a compensation method for the near corner effects are incorporated in the proposed formulation of SIBCs to improve the accuracy. The corresponding full 3D FEAs, which are validated by the agreement between their results and the data obtained from physical measurements, are used as the benchmark for this study. The proposed method is validated by the agreement between the results generated by the new quasi-3D simulations and the full 3D FEAs.