A novel numerical approach to calculate the time evolution of the three dimensional distribution of the magnetic field and forces in the end winding regions of large turbine generators is presented. The proposed approach is based on an integral formulation for nonlinear magnetostatic problems. Its main advantage is the reduction of the discretization to only the conductors and magnetic materials. In this paper the solution of a coupled magnetostructural problem consisting in the calculation of the mechanical stresses and deformations caused by the electrodynamic forces is presented. The analysis is based on a time stepping simulation where the currents are derived from the integration of a lumped parameter model

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Purpose - The paper aims to illustrate a numerical technique to calculate fields and inductances of rotating electrical machines. Design/methodology/ approach - The technique is based on an integral formulation of the nonlinear magnetostatic model in terms of the unknown magnetization. The solution is obtained by means of a Picard-Banach iteration whose convergence can be theoretically proved. Findings - The proposed method has been used to build a model of a large turbine generator. In particular, the influence of end effects on flux linkages has been computed. It has been demonstrated that the 2D solution underestimates the flux linkages as well as the no load voltage of 2 per cent, while the leakage fluxes are computed by the 2D solution with errors as high as 20 per cent. Originality/value - The method is advantageous in comparison to standard methods

A critical aspect of the 3D electromechanical analysis of rotating machinery is the treatment of motion. The paper proposes a technique taking advantage of the numerical characteristics of integral formulations. The motion can be "naturally" modelled because no mesh in the free space and, consequently, in the air gap is required. A frequency domain procedure is presented. It exploits a fixed point iteration technique to deal with magnetic nonlinearities. The procedure is able to determine a periodic steady state solution of a magneto quasi-static problem with both motional and trasformatoric effects. In order to highlight the effectiveness and the general validity of the approach, some numerical examples are presented, including the calculation of 3D Lorentz force density waveforms in massive non magnetic regions of a large turbine generator.

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