Benefit Assessment of Finite-Element Based Generator Saturation Model

Abstract

The accuracy with which power system transient stability limits can be calculated by computer simulation depends on the synchronous machine model. The saturation representation in the machine model can be improved now by non-linear magnetic finite element analyses of the machine. This paper describes steps taken to incorporate a saturation algorithm, based upon finite element analyses, into an 1100 bus power system stability program. Power transfer capability of a hypothetical system is compared using the finite element based algorithm versus the conventional algorithm based upon the manufacturer's open circuit saturation curve. INTRODUCT [ON: BACKGROUND AND MOTIVATIONSimulation studies are made to calculate stability limits of power systems as part of the quantitative analyses of alternatives facing system planners and operators.The alternatives include the generation dispatch and consequent amount of power transfer among and within utilities.Synchronous generators are modeled within these studies, to represent the nonlinear dynamics of the conversion from rotating shaft power to three-phase electric power.Prior work funded by EPRI in finite element analysis of generator modeling and validation by test (1,2,3] has shown that finite element analyses may be used to prepare generator models from design data, and that those models are well suited for calculation of the dynamic response (1,3] and steady-state conditions of a generator [1,2]. These results hold promise of improving the accuracy of power system analyses made by computer simulation.Finite-element based (FE) dynamic generator models (i.e., using linear operational inductances instead of the traditional T' , T'O, etc.) were developed in RP1288 [1,3]. The F dyn%mic models were used in simulation analyses of staged stability tests at the Bridger and Lambton stations; the comparisons indicate that the FE dynamic models are as accurate as models derived from on-line test methods [4]. That is, both FE models and models derived from tests appear to be more accurate than those based upon manufacturer's data (which are in turn based upon IEEE Standard 115 (5]). The major advantage in using FE dynamic models *A companion paper,

Online Parameter Estimation of Round Rotor Synchronous Generators Including Magnetic Saturation

“…Finally, the effect of saturation of generator inductances cannot be accounted for in off-line studies. Saturation is a critical concept in generator operation; in order to consider it in the estimation process, one has to account for the operating level of the generator at the particular estimation interval [1], [5]- [7]. The main effect of saturation is the decrease of the mutual inductances of the generator when the operating level of the machine exceeds a certain threshold limit.…”

On-Line Estimation of Synchronous Generator Parameters Using a Damper Current Observer and a Graphic User Interface

“…References [19] and [20] support this approach. Complex modeling of saturation may defeat the purpose of this study, which aims at a fast and reliable parameter estimation method with modest input data requirements.…”

“…An approach to improved saturation modeling using -axis saturation characteristics derived from finite-element analysis is shown in [19], [20]. Kundur [17] shows a method to calculate the saturation function.…”

“…On the left side of the output window, the estimated parameters are shown in per unit. The rms error on the lower right side of the estimator is a measure of confidence on the estimated parameters and is given by (20) where and is the vector of the estimated parameters. Finally, a confidence level is indicated and has three states: high, average or low.…”

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

“…To better conciliate these two objectives, finite-element method has been widely used for accurate prediction of step response tests such as flux decay and three-phase sudden short-circuits from which parameters may be extracted [5]- [11]. These approaches however suffer some shortcomings: reduced-order models are often used (only one damper winding per axis), the studied machines have small number of poles (not more than four), since dealing with a large number of poles seriously complicates the circuit arrangements in the armatures slots and FE domain mesh.…”