Numerical simulation of the end-winding deformations in the synchronous machine under symmetrical short-circuit conditions using FEM*

Abstract

In this paper the numerical simulation of the end-winding deformations in a synchronous machine under symmetrical short circuit conditions is presented. A sequentially coupled numerical simulation between an electromagnetic and a structural mechanical problem has been carried out. Owing to the short-circuit conditions, both problems are to be computed in the time-domain. Analysis of the time-variant magnetic field has been performed using the T, F -F formulation for the finite element method (FEM). This way, the influence of the induced eddy currents in the clamping-plates and in the housing of the machine on the magnetic field in the end-region of the generator has been taken into the account. In order to reduce the computational time, the non-conforming finite element (FE) mesh approach has been used to solve the electromagnetic problem. In each time-step the Lorentz forces in the end-winding have been calculated and carried over to the structural-mechanical model. These forces have been applied in the centre of the end-winding bars in order to provoke the transient excitation for the mechanical structure. A time-stepping scheme has been applied to calculate end-winding deformations in each time-step.

Development of a new simulation tool for computation of the synchronous generator end-winding deformations

“…7). Similar simulations performed for another 30MW synchronous generator have been validated with measurements in [8]. Such measurements have been rather rare owing to a very elaborate measurement set-up needed for measuring with piezo acceleration sensors or special optical sensors [8].…”

“…In analogy with the work [8] and [4] extensive measurements have been conducted in order to determine mechanical material properties for the winding bars as well as for the other construction parts. The verification of the mechanical system is done by comparing the numerical results of the FE modal analysis with the experimental results gained by frequency response functions of impact tests.…”

Finite element modelling of turbine generator stator end windings for vibration analysis

“…In FE models of stator end windings, to reduce computation costs, the stator bar is generally modelled as a single material with an equivalent elastic modulus [6,7,14]. In this model, the equivalent modulus is determined by fitting the calculated natural frequency of the first bending vibration mode of a stator bar to a measured value or calculated from the sum of the bending rigidities of the stator bar components as follows [14]:…”

“…Moreover, in FE models, stator bars comprising several materials are simplified. The whole stator bar is generally homogenised and modelled as a single material with an equivalent elastic modulus [4,6,7,14,15]. Since these models cannot reproduce the spatial distribution of the rigidity in a cross-section of the stator bar, they may degrade calculation accuracy.…”

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“…The first steps towards developing coupled techniques have been taken in the electromagnetic-thermal context in [30], and for electromagnetic-structural models in [33]. Further two papers [34][35] are concerned with the coupling between the electromagnetic field of the end-windings of synchronous machine and their deformations.…”