Timo Holopainen - Academia.edu (original) (raw)
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Papers by Timo Holopainen
Journal of Sound and Vibration - J SOUND VIB, 2007
In this work the effects of the electromechanical interaction on rotordynamics and vibration char... more In this work the effects of the electromechanical interaction on rotordynamics and vibration characteristics of cage rotor electrical machines were considered. An eccentric rotor motion distorts the electromagnetic field in the air-gap between the stator and rotor inducing a total force, the unbalanced magnetic pull, exerted on the rotor. In this paper a low-order parametric model for the unbalanced magnetic pull is coupled with a three-dimensional finite element structural model of the electrical machine. The main contribution of the work is to present a computationally efficient electromechanical model for vibration analysis of cage rotor machines. In this model, the interaction between the mechanical and electromagnetic systems is distributed over the air gap of the machine. This enables the inclusion of rotor and stator deflections into the analysis and, thus, yields more realistic prediction for the effects of electromechanical interaction. The model was tested by implementing ...
Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual p... more Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Holopainen, Timo P.; Arkkio, Antero
A new stiffened plate bending element for the vibration analysis of stiffened plate structures is... more A new stiffened plate bending element for the vibration analysis of stiffened plate structures is presented. The element can include the stiffeners anywhere within the element. The method can be called the master element technique. By this method the geometry idealization error can be reduced considerably, because there is no need to make remarkable geometrical simplifications. The use of master
The vibration behavior of a stiffened panel is investigated. The finite element method is employe... more The vibration behavior of a stiffened panel is investigated. The finite element method is employed for the computational analysis. The example structure is modeled using three different approaches. The main difference between the approaches is the way the stiffeners are modeled: as stiffener elements; or as flat shell elements. To estimate the errors, three element meshes on different levels of
2018 XIII International Conference on Electrical Machines (ICEM), Sep 1, 2018
Electric drivetrains have an almost rigid-body torsional vibration mode at a low natural frequenc... more Electric drivetrains have an almost rigid-body torsional vibration mode at a low natural frequency. If a torsional excitation occurs close to this frequency, the vibration amplitude may grow large, and the losses of the electrical machine may significantly increase. The possibilities to reduce or eliminate these additional losses are studied. When the machine is connected directly to the grid, the possibilities for vibration control mainly come from mechanical solutions. If the machine is fed from a frequency converter, there are several potential ways to suppress the additional losses. The torsional vibration control of electric drivetrains is studied from loss minimization point of view. This is the novelty of the paper.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
A 37 kW induction motor is modeled numerically taking into account the deterioration of the magne... more A 37 kW induction motor is modeled numerically taking into account the deterioration of the magnetic material properties at the cut edges of the core laminations. The magnetization properties and specific loss curves of the damaged edge and the intact material have been estimated from measurements published earlier. The deteriorated edges affect the iron losses of the machine in two distinct ways. First of all, the reduced permeability at the edges causes higher local flux densities elsewhere, which increases the losses. On the other hand, the cutting also has a direct effect on the specific loss density at the edges. By numerical simulations we show that the main effect is the latter one, and that the effect of decreased permeability remains low. The iron losses increase up to 37.6 %. The torque and active power of the machine are not much affected by the cutting, although also the current and resistive losses slightly increase due to the decreased permeability at the edges.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
Electrical steel sheets of motors and generators are usually shaped to the final form by punching... more 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.
The electromechanical interaction in electric machines induces additional forces between the roto... more The electromechanical interaction in electric machines induces additional forces between the rotor and stator. To study this interaction, a simple electromechanical model was developed. The mechanical behaviour was modelled by the Jeffcott rotor. The electromagnetic forces were described by a simple parametric model including two electormagnetic variables. The aim of the study was to investigate the effects of electromechanical interaction on rotordynamic instability in electric motors. If the new electromagnetic variables are interpreted as 'quasi-displacements', the interaction turns up in the equations of motion as additional damping, stiffness and circulatory terms. The electromagnetically induced damping and stiffness effects in electric motors have been studied previously. However, the effects of circulatory terms have been overrided in electric motors. It is well-known that the circulatory, i.e. cross-coupled stiffness, terms are a major source of instability in rotating machines. Thus, the presented model offers a new and simple explanation for the rotordynamic instabilty in electric motors. The numerical examples raised another source of instability. The system parameters may yield a negative-definite stiffness matrix (symmetric part), which destabilize the system without stabilizing forces.
IEEE Transactions on Industry Applications, 2016
Electromagnetic response of induction motors to torsional vibration is studied using space-vector... more Electromagnetic response of induction motors to torsional vibration is studied using space-vector and finite-element (FE) models. Comparison of the results shows that the skin effect in the rotor bars plays an important role, and the basic space-vector model has to be updated to a double-cage or triple-cage model. The results of the higher order models agree well with those of the FE analysis as long as motors with semiopen rotor slots are studied. In case of closed rotor slots, the saturation of the iron bridges on top of the bars causes problems in modeling accuracy.
Journal of Sound and Vibration - J SOUND VIB, 2007
In this work the effects of the electromechanical interaction on rotordynamics and vibration char... more In this work the effects of the electromechanical interaction on rotordynamics and vibration characteristics of cage rotor electrical machines were considered. An eccentric rotor motion distorts the electromagnetic field in the air-gap between the stator and rotor inducing a total force, the unbalanced magnetic pull, exerted on the rotor. In this paper a low-order parametric model for the unbalanced magnetic pull is coupled with a three-dimensional finite element structural model of the electrical machine. The main contribution of the work is to present a computationally efficient electromechanical model for vibration analysis of cage rotor machines. In this model, the interaction between the mechanical and electromagnetic systems is distributed over the air gap of the machine. This enables the inclusion of rotor and stator deflections into the analysis and, thus, yields more realistic prediction for the effects of electromechanical interaction. The model was tested by implementing ...
Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual p... more Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Holopainen, Timo P.; Arkkio, Antero
A new stiffened plate bending element for the vibration analysis of stiffened plate structures is... more A new stiffened plate bending element for the vibration analysis of stiffened plate structures is presented. The element can include the stiffeners anywhere within the element. The method can be called the master element technique. By this method the geometry idealization error can be reduced considerably, because there is no need to make remarkable geometrical simplifications. The use of master
The vibration behavior of a stiffened panel is investigated. The finite element method is employe... more The vibration behavior of a stiffened panel is investigated. The finite element method is employed for the computational analysis. The example structure is modeled using three different approaches. The main difference between the approaches is the way the stiffeners are modeled: as stiffener elements; or as flat shell elements. To estimate the errors, three element meshes on different levels of
2018 XIII International Conference on Electrical Machines (ICEM), Sep 1, 2018
Electric drivetrains have an almost rigid-body torsional vibration mode at a low natural frequenc... more Electric drivetrains have an almost rigid-body torsional vibration mode at a low natural frequency. If a torsional excitation occurs close to this frequency, the vibration amplitude may grow large, and the losses of the electrical machine may significantly increase. The possibilities to reduce or eliminate these additional losses are studied. When the machine is connected directly to the grid, the possibilities for vibration control mainly come from mechanical solutions. If the machine is fed from a frequency converter, there are several potential ways to suppress the additional losses. The torsional vibration control of electric drivetrains is studied from loss minimization point of view. This is the novelty of the paper.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
A 37 kW induction motor is modeled numerically taking into account the deterioration of the magne... more A 37 kW induction motor is modeled numerically taking into account the deterioration of the magnetic material properties at the cut edges of the core laminations. The magnetization properties and specific loss curves of the damaged edge and the intact material have been estimated from measurements published earlier. The deteriorated edges affect the iron losses of the machine in two distinct ways. First of all, the reduced permeability at the edges causes higher local flux densities elsewhere, which increases the losses. On the other hand, the cutting also has a direct effect on the specific loss density at the edges. By numerical simulations we show that the main effect is the latter one, and that the effect of decreased permeability remains low. The iron losses increase up to 37.6 %. The torque and active power of the machine are not much affected by the cutting, although also the current and resistive losses slightly increase due to the decreased permeability at the edges.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
Electrical steel sheets of motors and generators are usually shaped to the final form by punching... more 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.
The electromechanical interaction in electric machines induces additional forces between the roto... more The electromechanical interaction in electric machines induces additional forces between the rotor and stator. To study this interaction, a simple electromechanical model was developed. The mechanical behaviour was modelled by the Jeffcott rotor. The electromagnetic forces were described by a simple parametric model including two electormagnetic variables. The aim of the study was to investigate the effects of electromechanical interaction on rotordynamic instability in electric motors. If the new electromagnetic variables are interpreted as 'quasi-displacements', the interaction turns up in the equations of motion as additional damping, stiffness and circulatory terms. The electromagnetically induced damping and stiffness effects in electric motors have been studied previously. However, the effects of circulatory terms have been overrided in electric motors. It is well-known that the circulatory, i.e. cross-coupled stiffness, terms are a major source of instability in rotating machines. Thus, the presented model offers a new and simple explanation for the rotordynamic instabilty in electric motors. The numerical examples raised another source of instability. The system parameters may yield a negative-definite stiffness matrix (symmetric part), which destabilize the system without stabilizing forces.
IEEE Transactions on Industry Applications, 2016
Electromagnetic response of induction motors to torsional vibration is studied using space-vector... more Electromagnetic response of induction motors to torsional vibration is studied using space-vector and finite-element (FE) models. Comparison of the results shows that the skin effect in the rotor bars plays an important role, and the basic space-vector model has to be updated to a double-cage or triple-cage model. The results of the higher order models agree well with those of the FE analysis as long as motors with semiopen rotor slots are studied. In case of closed rotor slots, the saturation of the iron bridges on top of the bars causes problems in modeling accuracy.