Effects of the Slot Harmonics on the Unbalanced Magnetic Pull in an Induction Motor With an Eccentric Rotor (original) (raw)
The main proposal in this work is the theoretical- experimental analysis of the three-phase induction motor operation under different rotor slot inclination. The linear mathematical model(2) for the motor takes in consideration space harmonics of magnetomotive force (MMF) distribution. The motor feeding is done through a PWM inverter with sinusoidal modulation (PWSM), which means that the time harmonics must be also considered. This study allow us to draw some conclusions on how the slot rotor inclination can change the induction motor behavior.
Analytical analysis of rotor slot harmonics in the line current of squirrel cage induction motors
Journal of electrical engineering, 2006
This paper describes a new approach for analysing the effect of the space distribution of rotor bars in squirrel cage induction machines on the generation of rotor slot harmonics (RSH). An analytical expression of the stator current has been developed. The proposed expression is based on the linkage inductance expression derived using the winding function approach (WFA) and its decomposition into Fourier series. This approach describes the necessary relationship required for the presence of rotor slot harmonics and explains how the stator current is influenced by voltage unbalance. Simulations results have shown excellent match with theoretically predicted harmonic components.
Calculation of Radial Forces in Cage Induction Motors at Start—The Effect of Rotor Differential
IEEE Transactions on Magnetics, 2000
In this paper, the radial forces in an induction motor are calculated using finite element analysis. These radial forces (or unbalanced magnetic pull-UMP) are generated when the rotor is eccentric. The work illustrates the importance of higher winding harmonics and rotor differential leakage in the starting UMP. Examples of a 6 pole machine with 26 and 40 bar rotors show that increasing the bar number and air-gap length will reduce the UMP. Further studies are carried out using parameter variation and a 10-pole machine is also addressed, where experimental results exist, in order to validate the calculation.
2007
This paper presents the development of mathematical models and simulations of magnetic field, and mechanical vibration in a three-phase squirrel-cage induction motor. Its aim is to compare the vibration magnitude when the motor possesses different geometrical rotor-slot shapes. The cross sectional areas of two typical semi-closed slot shapes (rectangular and round shapes) are kept equally constant according to the IEEE standard. Under an assumption of sinusoidal motor excitation, the simulation works employ the finite element method (FEM) and the Newton-Raphson method to solve time varying nonlinear equations. The numerical solutions obtained indicate the electromagnetic force distribution over the motor cross sectional area. Such forces cause mechanical vibration in the motor. To evaluate this vibration, the displacement of stator inner perimeters was observed carefully. As a result, the round rotor slot gives 4.8% less vibration than the rectangular rotor slot does.
Air-gap force distribution and vibration pattern of Induction motors under dynamic eccentricity
Electrical Engineering, 2008
A method for determining the signatures of dynamic eccentricity in the airgap force distribution and vibration pattern of induction machine is presented. The radial electromagnetic force distribution along the airgap, which is the main source of vibration, is calculated and developed into a double Fourier series in space and time. Finite element simulations of faulty and healthy machines are performed. They show that the electromagnetic force distribution is a sensible parameter to the changes in the machine condition. The computations show the existence of low frequency and low order force distributions, which can be used as identifiable signatures of the motor condition by measuring the corresponding low order vibration components. These findings are supported by vibration measurements and modal testing. The low frequency components offer an alternative way to the monitoring of slot passing frequencies, bringing new components that allow to discriminate between dynamic eccentricity and rotor mechanical unbalance. The method also revealed a non linear relationship between loading, stress waves and vibration during dynamic eccentricity.
IEEE Access, 2021
A discrete winding function analysis (DWFA) based approach for the modelling of skewed rotor cage-type induction motor with minimal simulation time is presented in this paper. The rotor slot skew has a significant attenuating impact on principal slotting harmonics (PSH) or rotor slotting harmonics (RSH). These harmonics can play a significant role in sensor-less speed estimation and condition monitoring of induction machines. The advanced fault diagnostic algorithms are becoming increasingly dependent on the fast and accurate mathematical models of electrical machines. The most accurate models are based on the finite element method (FEM), but the computational complexity and the required simulation time make them unsuitable for model-dependent fault diagnostic algorithms. Moreover, as most models are 2D, they cannot incorporate axial asymmetries such as rotor slot skews. Furthermore, most analytical models, such as modified winding function analysis (MWFA), depend upon the continuous integration functions, increasing complexity while implementing them in the online environment in digital signal processing boards. To resolve all those issues, DWFA based model is proposed in this paper, which can simulate the majority of the faults in negligible time compared to the corresponding FEM models. The impact of slot skews and unbalanced power supply on the current spatial harmonics is studied, and the results are compared with the practical measurements taken from the laboratory setup.
THE IMPACT OF THE ROTOR SLOT NUMBER ON THE BEHAVIOUR OF THE INDUCTION MOTOR
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The impact of the rotor slot number selection on the induction motors is investigated. Firstly, analytical equations will reveal the spatial harmonic index of the air gap magnetic flux density, connected to the geometrical features and the saturation of the induction motor. Then, six motors with different rotor slot numbers are simulated and studied with FEM. The stator is identical in all motors. The motors are examined under time-harmonic analysis at starting and at 1440 rpm. Their electromagnetic characteristics, such as electromagnetic torque, stator current, and magnetic flux density, are extracted and compared to each other. The analysis will reveal that the proper rotor slot number selection has a strong impact on the induction motor performance.
—Recently, strong improvements have been made in the applicability of harmonic modeling techniques for electrical machines with slotted structures. Various implementations for permanent magnet motors and actuators have been investigated and applied in design and optimization tools. For the slotted structure of induction motors (IMs), however, the method has not been investigated very extensively yet. The main reasons for this are the complexity involved with modeling the large number of stator and rotor slots and the issues arising with the calculation of the induced rotor bar currents. In this work, a slotted harmonic model is implemented for a benchmark IM topology and a method to calculate the induced rotor bar current is investigated. The calculation results are validated by comparison to Finite Element simulations. It is shown that a good agreement is obtained for unsaturated operating conditions.
Recently, strong improvements have been made in the applicability of harmonic modeling techniques for electrical machines with slotted structures. Various implementations for permanent magnet motors and actuators have been investigated and applied in design and optimization tools. For the slotted structure of induction motors (IMs), however, the method has not been investigated very extensively yet. The main reasons for this are the complexity involved with modeling the large number of stator and rotor slots and the issues arising with the calculation of the induced rotor bar currents. In this work, a slotted harmonic model is implemented for a benchmark IM topology and a method to calculate the induced rotor bar current is investigated. The calculation results are validated by comparison to Finite Element simulations. It is shown that a good agreement is obtained for unsaturated operating conditions.
Comparative Study Of The Inductances Of An Induction Motor With Rotor Eccentricities
Eletrônica de Potência, 2010
In this work, the inductances of an induction motor, which rotor may be misaligned, are evaluated. Two types of analysis are performed: Analytical Method (AM) and Finite Element Method (FEM). For radial displacements, both methods show equivalent results but to evaluate inductances as a function of angular displacements, only with FEM was possible to get results as with AM it would be necessary intricate functions. The inductances obtained with FEM were included in simulations of a bearingless induction motor with split windings. This approach shows a good agreement with experimental results.