Timo Holopainen

Structural Finite Element Modeling of Electromechanical Interaction in Rotordynamics of Electrical Machines

In this work the electromechanical interaction in electrical machines is studied. The eccentric rotor motion distorts the electromagnetical fields in the air-gap between the stator and rotor of the machine inducing a total force, the unbalanced magnetic pull, exerted on the rotor shaft. In order to study the phenomenon a parametric electromagnetic force model is coupled with finite element structural model of the machine. The main objective of the work is to study the effects of the electromechanical interaction on vibration characteristics of electrical machines.Copyright

Identification of Magnetic Properties for Cutting Edge of Electrical Steel Sheets

Electrical steel sheets of motors and generators are usually shaped to the final form by punching. The punching and other cutting processes generate large plastic deformations and residual stresses. These are known to deteriorate the magnetic properties of the edge region. However, the characterization of this deterioration in the form of magnetic properties is missing. The main aim of this paper is to a method to identify the magnetic properties of the edge region based on experimental results. This approach is demonstrated by using previously presented test results for magnetic properties of rectangular strips. The width of these strips is varied, and thus, the share of the edge region to the whole can be used as a variable. Based on this variation a simple model is developed and the model parameters fitted to the experimental results. The correspondence between the calculated and experimental results is good.

Comparison of Modal Parameter Estimation Techniques for Electromechanical Rotordynamics of Cage Induction Motors

Electromagnetic fields in the air gap of an electric motor produce electromagnetic forces between the rotor and stator. These forces couple the electromagnetic system to the mechanical one. This electromechanical interaction changes the vibration behaviour of the machine, and it may decrease the critical speeds, induce additional damping or cause rotordynamic instability. The experimental validation of theoretical models of these effects requires modal parameter estimation techniques which are reliable and robust. The main aim of this paper is to compare available techniques for the modal parameter estimation. The studied methods were: a) peak picking, b) prediction error, c) polyreference least-squares complex frequency-domain, d) multiple output backward autoregression, and e) polyreference least-squares complex exponential. Experimental data for the comparison was obtained using a standard six-pole 18 kW induction motor equipped with a long flexible shaft. In addition, the theoretical values using a simple electromechanical rotor model were calculated for the test cases. Comparison showed the short-comings of traditional frequency domain techniques and some advantages of the modern frequency- and time-domain techniques.Copyright