Analysis of Unbalanced Magnetic Pull Calculation in Generators With Two Pole Pairs

2009 ◽  
Author(s):  
Lucia Frosini ◽  
Paolo Pennacchi ◽  
Carlo Maria Stoisser
Keyword(s):  
Time Instant ◽  
Harmonic Spectrum ◽  
Dynamical Behaviour ◽  
Air Gap ◽  
Dynamic Effects ◽  
Accurate Calculation ◽  
Unbalanced Magnetic Pull ◽  
Turbo Generator ◽  
Vibratory Analysis ◽  
Linear Effects

The modelling of the unbalanced magnetic pull (UMP) and the analysis of its effects on the dynamical behaviour of a large turbo-generator are presented in this paper. The UMP is the consequence of the electromagnetic forces acting upon rotor and stator generator surfaces and depends on the non-uniform air-gap distribution between rotor and stator. The flexibility and the dynamic effects on the generator behaviour are taken into account by an accurate calculation of the air-gap distribution depending on the position in a generic time instant of the rotor inside the stator. The method is then applied for the vibratory analysis of a two pole pair generator of a steam turbo-set: the harmonic spectrum of the UMP is evaluated and the presence of non-linear effects highlighted.

Computational Model for Calculating the Dynamical Behaviour of Generators Caused by Unbalanced Magnetic Pull and Experimental Validation

2007 ◽  
Author(s):  
Paolo Pennacchi ◽  
Lucia Frosini
Keyword(s):  
Power Plants ◽  
Experimental Validation ◽  
Radial Force ◽  
Dynamical Behaviour ◽  
Unbalanced Magnetic Pull ◽  
Turbo Generator ◽  
Proposed Model ◽  
Force Components ◽  
Electrical Motors ◽  
The Time Domain

This paper presents the modelling of the unbalanced magnetic pull (UMP) in generators and its experimental validation in a real machine. UMP is one of most relevant effects of electromechanical interactions in rotating machinery and manifests itself when rotor eccentricity causes an imbalance of the electromagnetic forces acting upon rotor and stator surfaces, so that a net radial force is developed. In small and stiff machines, like electrical motors, this phenomenon can be avoided by means of carefully assembling and manufacturing. On the contrary, big generators of power plants, supported by journal bearings, operate above their first critical speed behaving like flexible shafts, therefore the eccentricity of the active part of the rotor with respect to the stator is unavoidable. In the first part of the paper, an accurate model for calculating the UMP force is presented. This model is more general than those available in literature that are limited to circular orbits and is based on the actual position of the rotor inside the stator, therefore on the actual air gap distribution, regardless of the orbit type. The closed form of the non linear UMP force components is presented. In the second part, the experimental validation of the proposed model is presented, by considering a steam turbo generator of a power plant and by comparing the simulated dynamic behaviour in the time domain of the machine to the experimental one, without and with the excitation of the magnetic field in the generator.

Research of Flow Field and Temperature Field in 2D Annular Space of Air-Gap

2012 ◽  
Vol 214 ◽  
pp. 76-81
Author(s):  
Lu Tang ◽  
Yi Ping Lu ◽  
Hai Yan Deng ◽  
Zuo Min Wang
Keyword(s):  
Temperature Field ◽  
Boundary Conditions ◽  
Turbulent Flow ◽  
Flow Model ◽  
Radiation Heat Transfer ◽  
Air Gap ◽  
Rotating Flow ◽  
Annular Space ◽  
Concentric Cylinder ◽  
Turbo Generator

The flow in air-gap of turbo-generator was simplified to the rotating flow model in the 2D concentric cylinder annular space. According to the CFD principle, the rotating flow model equations of the laminar flow and the turbulent flow were solved with Finite Volume Method. After being compared with the analytical solution of the 2D concentric cylinder Couette shear flow, the 2D air-gap model, the boundary conditions and the calculation results were proved to be accurate. On the basis of the study of the velocity field, the energy equation and the radiation equation were added to study the temperature field in the annular space. The convection and the radiation heat transfer were considered under the first boundary conditions. The turbulent flow and temperature distribution of the annular space under the steady-state were analyzed

Rotating Shafts Affected by Transverse Cracks: A Sensitivity Analysis

2008 ◽  
Author(s):  
Nicolo` Bachschmid ◽  
Ezio Tanzi ◽  
Paolo Pennacchi
Keyword(s):  
Sensitivity Analysis ◽  
Element Model ◽  
Dynamical Behaviour ◽  
Crack Model ◽  
Transverse Cracks ◽  
Rotating Shaft ◽  
Shaft Line ◽  
Linear Approach ◽  
Turbo Generator ◽  
Rotating Shafts

The dynamic behaviour of heavy, horizontal axis, rotating shaft-lines affected by transverse cracks can be analysed in the frequency domain by a quasi linear approach, using a simplified breathing crack model applied to a traditional finite element model of the shaft-line. This allows to perform a series of analyses with affordable efforts. The analysis of the modelling procedure allows to define an approximated approach for simulating the dynamical behaviour, which allows to predict the severity of the crack excited vibrations, combined to modal analysis. this answers to the old-age question on how deep a crack must be to be detected by means of vibration measurements. The model of a 320 MW turbo-generator group has been used to perform a numerical sensitivity analysis, in which the vibrations of the shaft-line, and more in detail the vibrations of the shafts in correspondence to the bearings, have been calculated for all possible positions of the crack along the shaftline and for two different values of the depth of the crack. The calculated results confirm the predicted behaviour.

scholarly journals Study on the Unbalanced Fault Dynamic Characteristics of Eccentric Motorized Spindle considering the Effect of Magnetic Pull

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhan Wang ◽  
Wenzhi He ◽  
Siyuan Du ◽  
Zhe Yuan
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Air Gap ◽  
Fault Analysis ◽  
Experimental Results ◽  
Machining Accuracy ◽  
Motorized Spindle ◽  
Unbalanced Magnetic Pull ◽  
Static Eccentricity ◽  
Simulation Results

Unbalanced fault is the most common fault of high-speed motorized spindle, which is the main factor affecting the machining accuracy of high-speed spindle. Due to the unbalanced magnetic pull produced by the air gap eccentricity of the stator and rotor, the unbalanced vibration of the motorized spindle will be further aggravated. In order to explore the dynamic behavior and motion law of the unbalanced fault motorized spindle under the eccentric state, a dynamic model of the unbalanced fault of the high-speed motorized spindle considering the unbalanced magnetic pull was established. Taking the eccentric motorized spindle customized by the research group as the research object, the dynamic model is established, simulated, and analyzed, and the response change law of motorized spindle under the effect of different speed, unbalance, and air gap is obtained. The simulation results show that the unbalanced magnetic pull caused by static eccentricity will increase the unbalanced vibration of motorized spindle, and the unbalanced vibration will also increase with the increase of static eccentricity. The vibration caused by unbalanced magnetic pull does not increase with the increase of rotating speed. In frequency-domain analysis, when there is unbalanced magnetic pull, the peak appears at 0 Hz, and the amplitude of fundamental frequency vibration will increase with the increase of eccentricity. The experimental results show that the greater the eccentricity is, the greater the unbalance vibration of the motorized spindle is. The experimental results are consistent with the simulation results, which further verify the accuracy of the model. The research results lay a theoretical basis for fault analysis and diagnosis of coupling fault motorized spindle.

scholarly journals Sensitivity of Axial Velocity at the Air Gap Entrance to Flow Rate Distribution at Stator Radial Ventilation Ducts of Air-Cooled Turbo-Generator with Single-Channel Ventilation

Energies ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3442
Author(s):  
Yong Li ◽  
Weili Li ◽  
Ying Su
Keyword(s):  
Flow Velocity ◽  
Calculation Method ◽  
Air Gap ◽  
Test Method ◽  
Distribution Law ◽  
Stator Core ◽  
Flow Phenomenon ◽  
Turbo Generator ◽  
Ventilation Ducts ◽  
Ventilation Duct

In the design and calculation of a 330 MW water-water-air cooling turbo-generator, it was found that the flow direction of the fluid in the local stator radial ventilation duct is opposite to the design direction. In order to study what physical quantities are associated with the formation of this unusual fluid flow phenomenon, in this paper, a 100 MW air-cooled turbo-generator with the same ventilation structure as the abovementioned models is selected as the research object. The distribution law and pressure of the fluid in the stator radial ventilation duct and axial flow velocity at the air gap entrance are obtained by the test method. After the calculation method is proved correct by experimental results, this calculation method is used to calculate the flow velocity distribution of the outlets of multiple radial ventilation ducts at various flow velocities at air gap inlets. The relationship between the flow distribution law of the stator ventilation ducts and the inlet velocity of the air gap is studied. The phenomenon of backflow of fluid in the radial ventilation duct of the stator is found, and then the influence of backflow on the temperature distribution of stator core and winding is studied. It is found that the flow phenomenon can cause local overheating of the stator core.

Numerical Studies on the Flow Field of Stator and Air Gap for Large Air-Cooled Turbo-Generator

2012 ◽  
Vol 516-517 ◽  
pp. 970-975 ◽  
Author(s):  
Jia De Han ◽  
Guang Yu Hong ◽  
Lu Tang ◽  
Yi Ping Lu
Keyword(s):  
Flow Characteristics ◽  
Axial Direction ◽  
Air Gap ◽  
Cold Zone ◽  
Spiral Trajectory ◽  
Numerical Studies ◽  
Turbo Generator ◽  
Through Flow ◽  
Volume Method ◽  
Cooling Air

In order to study the flow characteristics in the stator and air gap for a large air-cooled turbo-generator with multi-air-zone of stator, a 3-D physical model includes the stator, rotor, and air gap was established. Numerical simulation was carried out by the finite volume method according computational fluid dynamics (CFD) principle, based on some corresponding boundary conditions and assumptions. The results show that the cooling air flowing into the air-gap through the outlets of rotor wedge rotates with rotor in the spiral trajectory and in higher velocity than ambient. The air velocity alternate high and low in axial direction. There are different flow characteristics in different regions of the air gap because of the influence of stator and rotor radial air injection and axial through flow. The air flowing into the air-gap from the cold zone forms the secondary flow near the side of stator.

Modelling of Magnetic Pull in Large Size Generator

2005 ◽  
Author(s):  
Paolo Pennacchi ◽  
Lucia Frosini
Keyword(s):  
Realistic Model ◽  
Dynamical Behaviour ◽  
Air Gap ◽  
Electrical Machines ◽  
Rolling Bearings ◽  
Actual Distribution ◽  
Large Size ◽  
Original Contribution ◽  
Tangential Forces ◽  
Radial Forces

This paper presents a method to analyze the dynamical behaviour of large size generators due to the magnetic pull. In rotating electrical machines, the electromagnetic radial forces acting upon rotor and stator surfaces are very large, but they are balanced when the rotor is concentric with the stator. Similarly, the tangential forces produce only an axially rotating moment. If the rotor becomes eccentric, then an imbalance of these forces occurs, so that a net radial electromagnetic force, known as Unbalanced Magnetic Pull (UMP), is developed. The models traditionally proposed in the literature to study the UMP can be considered as reliable in case of small size electrical machines supported by rolling bearings. On the contrary, in case of large size machines, such as turbo-generators supported by oil-film bearings, the approximation of circular orbits of the rotor is not acceptable. Nevertheless, the authors who have dealt with UMP in big size generators have disregarded that these rotor filtered orbits are elliptical and generally the orbit centres are not concentric with the stator. In order to provide a more realistic model and an original contribution, in this work the actual distribution of the air-gap length during the rotation will be determined in analytical terms, by taking into account the effects produced by the actual rotor orbit. The actual UMP is calculated by using the air-gap permeance approach and the simulation of the dynamical behaviour of a 320 MW generator is presented, showing the harmonic content of the UMP and the presence of non-linearities.

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