INDIRECT EVALUATION OF CONTACT PRESSURE BETWEEN FRAME AND STATOR CORE OF SELF-COOLED ELECTRIC MOTORS BY MEANS OF FINITE MODELS AND STRAIN GAUGES

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1 INDIRECT EVALUATION OF CONTACT PRESSURE BETWEEN FRAME AND STATOR CORE OF SELF-COOLED ELECTRIC MOTORS BY MEANS OF FINITE MODELS AND STRAIN GAUGES Rafael Beck WEG Electric Equipment Vinícius Sell Gonçalves WEG Electric Equipment

2 WEG A Brazilian company Plants: Brazil Argentina China Mexico India WEG controls all its production steps, from foundry and blanking press, to enameling and packaging. Some 2009 numbers: 19,500 employees and sales of R$5.11 billion Plant I Plant II

3 Problem sketch Vibration levels and efficiency are closely related to the contact pressure between frame and stator core, Schlensok et al. (2008) and Ishibashi et al. (2010); The higher the pressure, the higher the stiffness and heat transfer rate; Goals: 1st develop a methodology in order to determine contact pressure; 2nd connect the contact pressure to dynamic and thermal characteristics, such as stiffness and winding temperature. Electric motor on a test bench Heat generation in an electric motor

4 Methodology Preliminary work Special tooling of the frame (inside diameter and strain gauge regions); Strain gauge instrumentation; Insertion of the stator core and capture of frame deformation; Material characterization and choice of a plasticity model. Contact pressure determination CAD and FEM model construction; Iterative procedure until solution converges to the measured strain gauge values.

5 Tooling and gauge placing 160mm 160mm gauge C gauge D The strain gauges were placed symmetrically, covering a considerable portion of the stator length. gauge A gauge B

6 Instrumentation process just before stator core insertion Strain gauge Dummy

7 Deformation [1e-6m/m] Deformation [1e-6m/m] Deformation [1e-6m/m] Deformation [1e-6m/m] Stator insertion monitoring Strain gauge A(0) Strain gauge B(1) Time [s] Time [s] Strain gauge C(2) Strain gauge D(3) Time [s] -70 Time [s]

8 Stress [MPa] Stress [MPa] Material characterization Plastic strain [%] Strain [%] E [GPa] 90 0,24 By means of tension tests, the cast iron stress-strain and stress-plastic strain curves were obtained amongst the Poisson coefficient. These properties were used in Ansys.

9 CAD and FEM model construction strategy

10 CAD model The place where the gauges were attached were represented by lines in the way the mesh could be refined. Besides, two other lines were created in order to evaluate the deformation at the stator mid point. gauges stator mid point gauges

11 CAD model division Fins and feet were separated from the frame body, optimizing the mesh size.

12 Mesh Refinement of the gauge regions Triangular Solid187 with different element sizes used. Refinement of the contact surface

13 Contact definitions Steel-steel The interference value was created in a CAD model. Frictional contact type was chosen between stator and frame. Bonded was used between fins/feet and frame body.

14 Coodinate systems definitions gauges from the top y direction Stresses and displacements in x direction gauges from the bottom z direction Cartesian coordinate system rotated by 45 Gauge deformations Cylindrical coordinate system Stresses and displacements

15 Boundary conditions Symmetry through xy plane and displacement in x direction equals zero

16 Preliminary results

17 Gauge deformations Gauge Experimental deformation [ m/m] Finite element model deformation [ m/m] Individual Average (1) Individual Stator mid poit (2) Error (1)-(2) [%] A B C D The high error for gauges A and B (bottom) is due to residual deformations after frame tooling process. These deformations are not taken into account in the theoretical model.

18 S1 stresses

19 Radial stress and displacement Contact type Radial stress [MPa] Frictional Frictionless Rough Contact type Radial displacement [mm] Frictional Frictionless Rough

20 Conclusions / next steps Preliminary results show that the residual deformations of the frame after the tooling process exert direct influence on the experimental results. The numerical model doesn t consider such deformations and asymmetries, resulting in some divergences between numerical and experimental results; A new frame will be prepared, tighter than the previous one, and the tooling process must be improved in order to reduce geometric influence; Connect the contact pressure to dynamic and thermal behavior; Concerning the experimental modal analysis, it was observed that the model stiffness portion due to the stator core, is very high and significantly shifts the natural frequencies to higher levels.

21 References Structure-Dynamic Analysis of an Induction Machine Depending on Stator-House Coupling, Schlensok et al. (2008); Change of Mechanical Natural Frequencies of Induction Motor, Ishibashi et al. (2010).

22 Thank you!