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.

Asymptotic Fourier decomposition of tooth forces in terms of convolved air gap field harmonics for noise diagnosis of electrical machines

2009 ◽  
Vol 28 (4) ◽  
pp. 804-818 ◽  
Author(s):  
M. van der Giet ◽  
R. Rothe ◽  
K. Hameyer
Keyword(s):  
Air Gap ◽  
Electrical Machines ◽  
Content Type ◽  
Fourier Decomposition ◽  
Maxwell Stress Tensor ◽  
Convolution Process ◽  
Radial Forces ◽  
Space Vectors ◽  
Vibration Problems ◽  
The Relationship

PurposeThe electromagnetic excited audible noise of electrical machines can be mostly attributed to radial forces on stator tooth‐heads. The methodology proposed in this paper uses numerical field simulation to obtain the magnetic air gap field of electrical machines and an analytical‐based post‐processing approach to reveal the relationship between air gap field harmonics and the resulting force wave.Design/methodology/approachThe simulated air gap field is sampled in space and time and a two‐dimensional Fourier transform is performed. The convolution of the Fourier transformed air gap field by itself represents a multiplication in space time domain. During the convolution process, all relevant combinations of field waves are stored and displayed using space vectors.FindingsThe effectiveness of the proposed approach is shown on an example machine. Particular examples of individual force waves demonstrate how the approach can be used for practical application in analysis of noise and vibration problems in electrical machines. The proposed method is compared to the result of a Maxwell stress tensor calculation. It shows that the deviation is small enough to justify the approach for analysis purposes.Originality/valueThe combination of analytically understood force waves and the use of numerical simulation by means of air gap field convolution has not been proposed before.

The complete theory of cross-magnetization in uniform air-gap electrical machines

1988 ◽  
Vol 71 (1) ◽  
pp. 43-55 ◽  
Author(s):  
K. P. Kovács ◽  
R. Belmans ◽  
W. Geysen ◽  
A. Vandenput
Keyword(s):  
Air Gap ◽  
Electrical Machines ◽  
Complete Theory

Incipient Surge Detection in Large Volume Energy Systems Based On Wigner-Ville Distribution Evaluated On Vibration Signals

2021 ◽  
Author(s):  
Carlo Alberto Niccolini Marmont Du Haut Champ ◽  
Paolo Silvestri ◽  
Mario L. Ferrari ◽  
Aristide Fausto Massardo
Keyword(s):  
Research Field ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Rolling Bearings ◽  
Time Frequency ◽  
Rotating Machine ◽  
Large Size ◽  
Critical Issues ◽  
Volume Energy ◽  
Transient Operations

Abstract Compressor response investigation in nearly unstable operating conditions, like rotating stall and incipient surge, is a challenging topic nowadays in the turbomachinery research field. Indeed, turbines connected with large-size volumes are affected by critical issues related to surge prevention, particularly during transient operations. Advanced signal-processing operations conducted on vibrational responses provide an insight into possible diagnostic and predictive solutions which can be derived from accelerometer measurements. Indeed, vibrational investigation is largely employed in rotating-machine diagnostics together with time-frequency analysis such as smoothed pseudo-Wigner Ville (SPWVD) time-frequency distribution (TFD) considered in this paper. It is characterized by excellent time and frequency resolutions and thus it is effectively employed in numerous applications in the condition monitoring of machinery. The aim and the innovation of this work regards SPWVD utilization to study turbomachinery behavior in detail in order to identify incipient surge conditions in the centrifugal compressor starting from operational vibrational responses measured at significant plant locations. To this aim, an experimental campaign has been conducted on a T100 microturbine connected with different volume sizes to collect significant data to be analyzed. The results show that SPWVD is able to successfully identify system evolution towards an unstable condition, by recognizing different levels and features of the particular kind of instability that is going to take place within the plant. Instability phenomena regarding rolling bearings have also been identified and their interaction with surge onset has been investigated for diagnostic purposes.

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.

Special air-gap element for 2-D FEM analysis of electrical Machines accounting for rotor skew

2005 ◽  
Vol 41 (5) ◽  
pp. 2020-2023 ◽  
Author(s):  
G.D. Kalokiris ◽  
T.D. Kefalas ◽  
A.G. Kladas ◽  
J.A. Tegopoulos
Keyword(s):  
Fem Analysis ◽  
Air Gap ◽  
Electrical Machines ◽  
Gap Element

scholarly journals Estimating Apple Fruit Size Distribution from Early-season Fruit Diameter Measurements

HortScience ◽  
2019 ◽  
Vol 54 (11) ◽  
pp. 1947-1954
Author(s):  
Richard P. Marini ◽  
James R. Schupp ◽  
Tara Auxt Baugher ◽  
Robert Crassweller
Keyword(s):  
Size Distribution ◽  
Fruit Size ◽  
Apple Fruit ◽  
Fruit Weight ◽  
Regression Equations ◽  
Full Bloom ◽  
Actual Distribution ◽  
Early Season ◽  
Large Size ◽  
Fruit Diameter

In three experiments, diameters of apples representing 7% to 30% of the fruit on a tree were measured at ≈60 days after full bloom. Using previously published regression equations, the early-season fruit diameter values were used to estimate apple fruit weight at harvest (FWH). At harvest, all fruit on sample trees were weighed and the distributions of estimated FWH for fruit measured early in the season were compared with distributions of the actual FWH for whole trees. Actual FWH was normally distributed for only one of the three experiments. Although the estimated mean FWH averaged for the 10 trees was within 9% of the actual mean FWH for all three experiments, the distribution of estimated FWH differed significantly from the actual distribution for all three experiments. All fruit were then assigned to appropriate commercial fruit sizes or box counts (number of fruit/19.05 kg). Fruit size tended to peak on the same four box counts for the estimated and actual populations, but the estimated populations had too few fruits in the small- and large-size box counts. Using early-season estimates of FWH, commercial apple growers and packers can predict fairly accurately the percentage of the crop that will fall into the peak box counts, but a more accurate early-season estimate of the fruit size distribution will likely require measuring 50% of the fruit on a tree.

scholarly journals A Novel Analytical Method to Calculate Wheel-Rail Tangential Forces and Validation on a Scaled Roller-Rig

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Nicola Bosso ◽  
Nicolò Zampieri
Keyword(s):  
Contact Problem ◽  
Analytical Method ◽  
Efficient Algorithm ◽  
Experimental Tests ◽  
Dynamical Behaviour ◽  
Contact Forces ◽  
Strongly Nonlinear ◽  
Fast Solution ◽  
Tangential Forces ◽  
Roller Rig

The study of railway dynamic strongly depends on the estimation of the tangential forces acting between wheel and rail. Simulation of the dynamical behaviour of railway vehicles is often performed using multibody codes, and the calculation of the contact forces must be efficient and accurate, even if the contact problem is strongly nonlinear. Therefore, the contact problem is still of great interest for researchers. This work proposes an analytical and efficient algorithm to calculate wheel-rail tangential forces. The proposed method is compared with the most commonly used algorithms under different conditions. In addition, experimental tests are performed on a scaled prototype on roller-rig to demonstrate that the method can be easily adjusted using experimental results. The benefit of the proposed method is to provide an analytical and fast solution, able to obtain accurate results and to allow corrections based on empirical evidence.

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