Krzysztof Komeza

Finite-Element and Analytical Calculations of No-Load Core Losses in Energy-Saving Induction Motors

This paper presents a no-load core loss analysis of a three-phase energy-saving small-size induction motor supplied by a sinusoidal voltage. In the field-circuit approach, the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite-element method. The discrete Fourier transform is used to analyze the magnetic flux density waveforms in each element of the motor model. The rotational aspect of the field is included by introducing a correction to the losses generated by the first harmonic of magnetic flux density. The core losses in each element are evaluated using a loss curve measured on a toroidal core at different frequencies. Finally, an approximate analytical formulation is derived for rapid field computation. The results are compared with measurements.

Performance Characteristics of a High-Speed Energy-Saving Induction Motor With an Amorphous Stator Core

This paper presents operational characteristics of a small induction motor with the stator core made of amorphous laminations, supplied from mains or a frequency inverter at 50, 100, and 200 Hz. Calculations were performed using field-circuit and equivalent circuit approaches, taking account of nonlinearity and additional losses, both in the core and in the windings. Data for mechanical losses, magnetization curves, and magnetic losses of the amorphous material were experimentally obtained; magnetic measurements were taken as a function of magnetic flux density in the frequency range up to 2000 Hz. Calculated results are compared with measurements.

Equivalent Permeability of Step-Lap Joints of Transformer Cores: Computational and Experimental Considerations

The paper develops an efficient computational method for establishing equivalent characteristics of magnetic joints of transformer cores, with special emphasis on step-lap design. By introducing an equivalent material, the method allows the real three-dimensional structure of the laminated thin sheets to be treated computationally as a two-dimensional problem and enables comparative analysis of designs. The characteristics of the equivalent material are established by minimizing the magnetic energy of the system. To verify the proposed approach, a series of experiments have been conducted. First, the anisotropic characteristics of the step-lap were established, and then space components of the flux density at specified positions measured. This enabled detailed analysis of the flux distribution in the step-lap region, in particular the way in which the flux travels between the laminations close to the air-gap steps. Encouraging correlation between the homogenized 2-D model and experiment has been observed.

The highly efficient three-phase small induction motors with stator cores made from amorphous iron

Applies the field/circuit two‐dimensional method and improved circuit method to engineering designs of the induction motor with stator cores made of amorphous iron. Exploiting of these methods makes possible computation of many different specific parameters and working curves in steady states for the “high efficiency” three‐phase small induction motor. Compares the results of this calculation with the results obtained for the classical induction motor with identical geometric structure.

Experimental and Numerical Characterization of Magnetically Anisotropic Laminations in the Direction Normal to Their Surface

This paper proposes a mixed experimental/numerical technique to characterize magnetic laminations in the direction normal to their surface. The principle, which uses static excitation to avoid errors caused by eddy currents, is explained and a specific test bench is proposed. Measurements of the magnetic flux density are made using a sensor being moved in and out of the air gap and are supplemented by 3-D numerical modeling where the final characteristic is obtained through iterations until the computed and measured values agree within assumed tolerance. Comparisons with previously published approach based on an analytical model are made and specific properties of the characteristic of anisotropic laminations are discussed.

Application of circuit and field‐circuit methods in designing process of small induction motors with stator cores made from amorphous iron

Purpose – To investigate the use of amorphous iron as the stator core material to increase the efficiency of electric machines in serialised production.Design/methodology/approach – In the design process of a new structure for the induction motor with a stator core made from amorphous iron it is necessary to apply the circuit method and the field‐circuit method. The use of the circuit method allows quick calculations of many versions of the designed motor, but the use of the field‐circuit method is necessary for verification of the maximal value of the flux density in the entire area of the cross‐sections of the motor core.Findings – A new construction for the small induction motor with the stator core made from amorphous iron was designed based on the classical structure of the four‐pole induction motor. In the designed motor a decrease of the electric energy costs was observed, which is much bigger than the material costs, and in effect lower total costs for the designed motor were obtained.Practical im...

Field and circuit calculation of the core losses in the energy-saving small-size induction motor

This paper presents no-load core loss analysis of 3-phase energy-saving small size induction motor supplied by sinusoidal voltage. In field-circuit part the distribution and changes of magnetic flux densities of the motor are computed by using time-stepping FEM. Discrete Fourier Transform is used to analyze the magnetic flux density waveforms in each element of the motor model. Rotational aspect of the field is included by introducing correction to first harmonic of alternating losses. Core losses in each element are evaluated using core loss curve measured on toroidal core at different frequencies. In addition, rapid circuit method is presented. The results are compared with the measurements.

Computer modelling of 3D transient thermal field coupled with electromagnetic field in three‐phase induction motor on load

Purpose – The purpose of this paper is to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for three‐phase induction motor (IM) on nominal load. An additional purpose is verification empiric expressions of the heat transfer and equivalent thermal conductivity coefficients for external faces and air zones in analysed motor taken from literature.Design/methodology/approach – The numerical investigations proposed in this paper are based on 3D finite element models for thermal and electromagnetic fields analysis. Electromagnetic analysis includes iron core losses. It gives additional heat sources to thermal analysis. Heat transfer and equivalent thermal conductivity coefficients are assessed applying empiric expressions. Thermal model is experimentally validated.Findings – The results of calculations and experimental test shows that heat transfer coefficient for external zones taken from literature does not guarantee the equal accuracy o...

Dependence of the contact resistance on the design of stranded conductors.

During the manufacturing process multi-strand conductors are subject to compressive force and rotation moments. The current distribution in the multi-strand conductors is not uniform and is controlled by the transverse resistivity. This is mainly determined by the contact resistance at the strand crossovers and inter-strand contact resistance. The surface layer properties, and in particular the crystalline structure and degree of oxidation, are key parameters in determining the transverse resistivity. The experimental set-ups made it possible to find the dependence of contact resistivity as a function of continuous working stresses and cable design. A study based on measurements and numerical simulation is made to identify the contact resistivity functions.

Computer modelling of 3D transient thermal field coupled with electromagnetic field in one‐phase induction motor with locked rotor

Purpose – This paper aims to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for a one‐phase induction motor with locked rotor for nominal and lowered voltage excitation values. It also aims to prepare a calculating method for the average heat transfer coefficient for natural convection from the induction motor housing external face.Design/methodology/approach – The numerical investigations proposed are based on 3D finite element models for thermal and electromagnetic fields analysis and 3D volume element model for average heat transfer coefficient calculations. The thermal model is experimentally validated.Findings – The paper provides a numerical method to calculate average heat transfer coefficient for the induction motor housing external faces. This coefficient is shown as a temperature function. Temperature variations in the various parts of the induction motor with locked rotor are calculated. The calculation results are compa...