Coupled finite-element/state-space modeling of turbogenerators in the abc frame of reference-the no-load case

Abstract

This first of two companion papers centers on applying a coupled finite-element/state-space technique to the determination of self and mutual winding inductances of a 733-MVA turbogenerator and computing its open-circuit characteristic, in the natural abc frame of reference. In this method, the apparent self and mutual inductance profiles of the armature and field windings, expressed as functions of rotor position angle, are computed from a series of magnetic field solutions performed at uniformly-distributed samples of rotor positions covering the entire 360° electrical cycle, using the energy perturbation method. These inductances, which are obtained at no-load for three different excitation levels, include the full effect of space harmonics introduced by the magnetic circuit geometry, winding layouts and magnetic circuit saturation. The abc-frame/finite-element computed open-circuit characteristic is in excellent agreement with the test results. This computed no-load set of parameters forms the initial data for simulation of the full-load performance given in the companion paper, including the full impact of space harmonics and saturation on the flux linkage, current and voltage waveforms, and other performance parameters.Keywords-Finite Elements, Turbogenerators, ABC Frame of Reference, Inductances and Reactances of Machines. I N T R O D U C T I O NSynchronous machine models used in stability studies are usually formulated under the well-known two-axis theory by transforming (a,b,c) stator variables into fictitious direct (d) and quadrature (9) axes variables. The parameters in these models are normally determined from standard open-circuit and short-circuit tests, load rejection tests, or from frequency-response measurements [I,2]. In all of these methods, saturation effects are approximated by empirical formulas which, in many cases, yield results with reasonable engineering accuracy [3]. It is recognized, however, that only a full detailed magnetostatic field solution of Maxwell's equations can accurately reflect the impact of rotor saliency, slotting, rotor-to-stator relative motion, saturation, winding layouts and other effects.by t h e IEEE E l e c t r i c Machinery Committee of t h e IEEE Power Engineering S o c i e t y f o r p r e s e n t a t i o n a t t h e IEEE/PES 1994 Summer Meeting, San F r a n c i s 1993; made a v a i l a b l e f o r p r i n t i n g June 1 , 1994.A paper recommended and approved Two-dimensional (2D) finite-element (FE) and finitedifference (FD) methods have been shown t o be a viable alternative for obtaining synchronous machine parameters numerically [4-81. These developments in the F E and F D methods were based on work [5-81 where the magnetic field in turbogenerators under load was modeled with the help of a tworeaction (d-q) theory-based method. In these works, the stator (a,b,c) phase coils and currents were largely modeled by sinusoidal current sheets from which the stator slot (armature) currents were obtained. More recently, coupled 3D-FE/statespace (CFE-SS) models in t...

Prediction of the Inductance in a Synchronous Linear Permanent Magnet Generator

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Line-to-line short-circuit-based finite-element performance and parameter predictions of large hydrogenerators

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Steady state analysis of synchronous generators by a coupled field-circuit method

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