Modal analysis of operational end winding vibrations

Kreischer, Christian; Kulig, Stefan; Thien, Dagmar

doi:10.1109/iemdc.2011.5994775

Cited by 4 publications

(4 citation statements)

References 4 publications

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“…By decomposing the overall vibration into individual modal forms, described in Kreischer et al (2011), it can be judged whether the end winding has a local or global loosening or if it is excited in resonance.…”

Section: Modern Methods For Vibration Monitoringmentioning

confidence: 99%

Modern methods to monitor end winding vibrations in turbo-generators

Kreischer

2019

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Purpose Problems caused by end winding vibrations in power plant generators have become increasingly evident in recent years and reveal a need for monitoring and diagnostic systems. An increasing number of operational outages are caused by failures of the winding insulation or the conductor itself due to end winding vibrations. Meanwhile, it is clear that the condition of the end winding must be continuously monitored during operation to detect ineffective end winding support in time and to plan the repair. Design/methodology/approach In this paper, the complex and nonlinear excitation mechanisms in large machines are presented and modern methods for vibration monitoring are described. Through a consistent use of vibration monitoring in the end winding area as well as the vibration diagnosis done by experts, damage mechanisms can be detected at an early stage, repair measures can be planned and serious damage owing to a weakened main insulation can be avoided. Findings By combining modal analysis and trend monitoring in relation to the learned vibration behaviour, the end winding condition can be assessed in a differentiated manner and changes in the end winding structure can be detected early. Originality/value Finally, an assessment for a two-pole, air-cooled turbo generator is proposed.

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Section: Modern Methods For Vibration Monitoringmentioning

confidence: 99%

Modern methods to monitor end winding vibrations in turbo-generators

Kreischer

2019

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“…where E eq is the equivalent Young's modulus or shear modulus, and f i is the volume fraction of the components. The whole stator bar is generally homogenised and modelled as a single material by using classical equations like (7) and (8); however, this model cannot reproduce the spatial distribution of rigidity in a cross-section of the stator bar. Moreover, when the difference in the first term and the second term on the right of equation 7is large, the accuracy of the calculated bending stiffness of the bar in the x-and y-directions decreases because the equivalent Young's modulus is obtained by averaging the bending stiffness in both directions.…”

Section: Calculation Of Stator Bar Equivalent Modulimentioning

confidence: 99%

“…In the case of the isotropic model, equivalent Young's modulus E z was evaluated from (7), and the other elastic moduli were calculated under the assumption that the conductor bar is an isotropic material with a Poisson's ratio of 0.3. In the anisotropic model, E z equalled that of the isotropic model and the other elastic moduli were obtained from (8). In the proposed model, all elastic moduli were calculated by…”

Section: Fe Analyses Of Equivalent Elastic Moduli Of Conductor Barmentioning

confidence: 99%

“…These studies demonstrated that the vibration modes that are most sensitive to the electromagnetic forces are the four-and eight-node vibration modes for two-and four-pole generators, respectively. The excitabilities of each of the vibration modes have also been quantitatively analysed [8,9] and a transient vibration analysis under a fault condition has been reported [10]. In the latter study, end winding vibration responses during a three-phase short circuit were measured and compared with calculated responses.…”

Section: Introductionmentioning

confidence: 99%

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

Iga

Takahashi

Yamamoto

2016

IET Electric Power Applications

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In this study, the authors present methods for accurately modelling the bindings and the stator bars of turbine generator stator end windings for vibration analyses. The bindings are modelled with beam elements and multipoint constraint equations to take account of the bending, twisting, and shearing rigidities of the bindings. To reproduce the spatial distribution of rigidity in a cross-section of the stator bar, the bar is modelled as a composite material comprising a conductor bar with equivalent elastic moduli and ground insulation. The accuracies of the developed binding and stator bar models are verified by comparing measured natural frequencies of binding test pieces and stator bar specimens with calculated values. The developed models and conventional models are applied to the natural frequency analyses of stator end windings, and then the effects of the modelling methods on the calculation accuracy are investigated. While the maximum calculation errors of the conventional models are more than 12%, the calculation results of the developed models agree with the measured values within an error of 7%. Accordingly, for accurately calculating the end winding natural frequencies, end winding finite element models need to take the binding rigidities into account and reproduce the rigidity distribution of the stator bar.

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Measurement Methods for End Winding Vibrations of Large Electrical Machines

Kreischer

2019

Lecture Notes in Electrical Engineering

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Modal analysis of operational end winding vibrations

Cited by 4 publications

References 4 publications

Modern methods to monitor end winding vibrations in turbo-generators

Modern methods to monitor end winding vibrations in turbo-generators

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

Measurement Methods for End Winding Vibrations of Large Electrical Machines

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