Jan Sobra

Key construction aspects of resonant wireless low power transfer system

The paper discuses an important construction aspects of resonant wireless power transfer (WPT) system for small portable devices. It focuses mainly on key electrical parameters of the systems resonant linkage and its proper construction shape. All presented theoretical presumptions are consequently verified by detailed measurement.

Computation of stator vibration of an induction motor using nodal magnetic forces

In the case of rotating electrical machines, the magnetic forces acting on the stator teeth are the principal electromagnetic cause of vibrations. Based on this fact, this paper presents a method to compute the vibrations of an induction motor with the aid of magnetic nodal forces. An accurate computation of local or nodal forces is essential in problems pertaining to vibration and noise analysis of electrical machines. Virtual work method is utilized here to compute the nodal forces as the local derivative of magnetic energy from the Finite Element (FE) solution of the magnetic field problem. The magnetic problem is then coupled to an elasticity solver to calculate the displacement due to these forces. The nodal force method is implemented in an open source finite element software Elmer and the entire magneto-mechanical computation is carried out in the same open source tool. The calculated results are then compared to vibration measurements of the motor.

Determination of the force caused by broken rotor bar and static eccentricity in an induction machine

The paper deals with the force acting in the air-gap of an induction machine within unusual operating states, e.g. static eccentricity and broken rotor bar. Force is determined via FEM model of real induction motor. The study focuses on two special faulty operating states. First, the motor is under static eccentricity only. Second, static eccentricity and broken rotor bar are present simultaneously in the machine. The comparison of both cases is discussed in the paper.

Analysis of rotor's eccentricity influence on bearing load of induction machine

To ensure reliable drive with an induction machine requires deep insight in electro-mechanical dynamics during its operation. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive components. This paper focuses on complex modeling of machines behavior in case of eccentrically placed rotor. The life time of machines bearing becomes very important issue of machines maintenance and reliability and is markedly influenced by any unbalanced forces acting on the rotor. The rotor eccentricity is one of the most significant aspects making machines bearing loaded by strong unbalanced magnetic pull. Only the complex flexible model of the rotor considering all unbalanced rotor forces can provide us the very detailed information about the bearing load. The methodology of determination of such loading is applied to the 11 kW squirrel-cage induction machine.

Mechanical vibration analysis of induction machine under dynamic rotor eccentricity

This paper analyzes the mechanical vibration frequency spectra of a healthy squirrel cage induction machine and the identical machine operating under the dynamic rotor eccentricity. Radial vibrations are evaluated based on the experimental data in no-load and nominal load steady state operations. The main attention is paid to the rotational frequency and twice line frequency vibration components. Necessity of further study is pointed out.

Vibration and stator current spectral analysis of induction machine operating under dynamic eccentricity

This paper deals with the squirrel-cage induction machines rotor fault diagnostics - dynamic eccentricity concretely - in nominal steady state. The particular fault diagnostic is carried out with both vibration and stator current frequency spectra analyses. Besides the machine with faulty rotor the same analyses on the machine with a healthy one are performed as a reference point. The comparison of both diagnostic methods is discussed.

Numerical calculation of the effect of the induction machine load on the air gap magnetic flux density distribution

The subject of this paper is the calculation of the induction machine air gap flux density distribution. Following previous paper, the parameters affecting the distribution are integrated to create the final no-load flux density distribution. The no-load calculations are valid for every type of winding and can be applied to almost every type of electric machine. To calculate the flux density distribution in loaded condition, the magnitude and phase shift of the rotor current have to be calculated. The rotor magnetomotive force reaction distribution is calculated according to the stator calculations. Based on the equivalent circuit of the machine, the flux density distribution of variable load condition can be calculated. All numerical results are compared with the finite element analysis calculations and the distribution and spectral analysis of the air gap flux density are evaluated in this paper.

The effect of space harmonic components in the air gap magnetic flux density on torque characteristic of a squirrel-cage induction machine

The paper discusses the effects of harmonic content of the air gap magnetic flux density on torque characteristic of a squirrel-cage induction machine. It mainly focuses on behavior of the harmonic content during the operation and quick prediction of its torque performance using steady state analysis. The study combines harmonic finite element analysis with analytical approach.

Comparison of Vibration and Noise Measurement of Induction Machine Under Static Eccentricity

The paper is focused on the comparison of vibration and emitted noise measurement of induction machine under static eccentricity in an environment with steady acoustic noise producing facilities. Such an environment can introduce for example simple industrial drive stand operating under constant load in a closed room. The analyses are focused to the frequency spectrum up to 1500 Hz which allows us to validate the frequency spectrum of emitted noise by vibration measurement. The analyzed frequency band is sufficient considering vibration response of implemented fault. The analyses of healthy machine are carried on as well to get the reference point.

Natural frequencies of small squirrel cage induction machine rotor — Finite element model optimization

The paper deals with possibilities of geometry simplification for FE structural model calculating natural frequencies and mode shapes of rotor of small squirrel-cage induction motor. Proposed simplifications lead to the computing time savings while good result accuracy is preserved. All results are verified by experimental measurement.