Ilona Iatcheva

3-D Electromagnetic Force Distribution in the End Region of Turbogenerator

The paper deals with detailed investigation of the electromagnetic forces in the end zone of turbine generator. The electromagnetic field is analyzed using 3-D FEM computation. The regions of interest are the stator and rotor end cores including the zone of the teeth and the end windings. The dynamic behavior of the local electromagnetic force densities is studied in accordance with the working mode. Two modes at the leading and at the lagging power factor are considered. Comparison between the ratio of the local electromechanical loads under considered modes and the relevant loads at the rated mode is discussed and appropriate conclusions are drawn. Calculations are implemented on a 200 MW turbine generator.

Electromagnetic field modeling and determination of parameters in teaching electrical engineering

The paper presents the possibilities, advantages and authors experience in application of electromagnetic field modeling in the teaching process in the study of electrical engineering specialties. The aim is to demonstrate how on the basis of computer simulations, the students can examine the field distribution for different geometry and operating conditions of given device. In addition, students are introduced to the opportunity how to determine some specific device parameters and characteristics, whose varying enables optimization of system behavior. Examples are given for FEM modeling of electromagnetic field distribution in different devices and determination of parameters and characteristics, such as capacitance, inductance, magnetic flux, energy and forces.

The production tolerances influence on the optimal solution

Purpose – The purpose of this paper is to introduce a method for evaluating the production tolerances influence on the practically realized optimal solution of electrotechnical devices. The influence is estimated by the optimal solution range defined with a given probability.Design/methodology/approach – Because of the tolerances nature, the paper is in probabilistic categories. The accent is put on the cases when the mathematical description of the cost function is analytical, for example polynomial found on the basis of the design of experiments and response surface methodology. The optimal solution range is defined with a given probability. The governing equation is Chebychevs inequality. In some cases, Chebychevs inequality would be rather weak but the advantage is that it is valid for all kinds of probabilistic distributions.Findings – A numerical example – an electrical machine – is considered with respect to variances in the magnetic characteristics of the stator and rotor core electrotechnical s...

Modeling of electric and heat processes in spot resistance welding of cross-wire steel bars

Abstract The aim of this work is the modeling of coupled electric and heat processes in a system for spot resistance welding of cross-wire reinforced steel bars. The real system geometry, dependences of material properties on the temperature, and changes of contact resistance and released power during the welding process have been taken into account in the study. The 3D analysis of the coupled AC electric and transient thermal field distributions is carried out using the finite element method. The novel feature is that the processes are modeled for several successive time stages, corresponding to the change of contact area, related contact resistance, and reduction of the released power, occurring simultaneously with the creation of contact between the workpieces. The values of contact resistance and power changes have been determined on the basis of preliminary experimental and theoretical investigations. The obtained results present the electric and temperature field distributions in the system. Special attention has been paid to the temperature evolution at specified observation points and lines in the contact area. The obtained information could be useful for clarification of the complicated nature of interrelated electric, thermal, mechanical, and physicochemical welding processes. Adequate modeling is also an opportunity for proper control and improvement of the system.

Investigation of spot resistance welding system based on 3D field modeling using FEM

The paper presents some results of study of the electric and thermal processes, taking part in contact resistance welding of cross-wire steel bars. The investigations are based on 3D FEM modeling of the electric and temperature field distribution. Several successive stages of the welding process are considered in the study, taking into account the changes, corresponding to the increase of the contact area and decrease of the contact resistance during the welding.

Bidirectional DAB DC-DC converter with hysteresis current mode control

A new modulation strategy with Hysteresis Current Mode Control for Bidirectional Dual Active Bridge (DAB) is proposed in the paper. A simulation model for Buck and Boost mode of operation is developed and implemented in the MATLAB/SIMULINK environment. The value of the calculated leakage inductance is verified using COMSOL program. The proposed Hysteresis Current Mode Control allows combining the advantages of Current Fed Bidirectional Converter and Bidirectional DAB.

Electromagnetic Flow Meter Field Distribution Maximizing Device Sensitivity

The presented paper deals with determination of the excited magnetic field magnitudes at different points around the device guarantying maximal output signal. Investigated object is electromagnetic flow meter. The output signal is polarization voltage through the circle cross section of the polarization transducer between its electrodes. Except the magnetic field distribution some geometrical parameters of the device and physical characteristic of the inside moving dielectric are varied. The forward field problem is solved by the use of the Comsol, version 5.0 software package. The inverse problem is solved using skills of the Response Surface Methodology (RSM), Design of Experiments (DOE) and Nonlinear Programming. The numerical approach for finding optimal magnetic field distribution is discrete at chosen points. Applying spline interpolation after that the analytical description of the optimal field distribution is defined.

Modelling of the Electric Field Applied to the Ensembles of Microparticles

The paper deals with modelling of the time varying electric field, applied to composites structures of inorganic materials (containing metal and metal oxide). The structural changes at the initials stages of sintering, characterised by the number of contact per particle and an increase of the areas of interparticle contact have been modelled and examined. The aim of study was estimation of the electric field strength, current density, power losses and forces, acting along the contact area between particles. The field models have been obtained using finite element method and QuickField 5.6 software package.

Modeling of the Processes in a Resistive Glass Melting Furnace in Heat Treatment of Glassware with Complex Form

The paper deals with modeling of steady state and transient thermal processes in a small resistance electric furnace for melting and heat treatment of high quality glass products. The device is designed to obtain molten glass, which can meet the multiple requirements for handling glass and is used for producing of artistic glass sculptures. The temperature field distribution has been studied by 3D FEM modeling of heating and cooling processes under variable conditions specified, depending on the supply power, technological limitations and users’ requirements. Experimental studies have been also carried out in order to verify numerical modeling. The obtained results are reliable basis for optimal control, high efficiency and ensuring of required glass quality.

Study of the relationship between the distribution of the power and temperatures in a small resistive art glass melting furnace

The subject of the investigation is a small electric resistance furnace with two technological regimes of melting glass - in a crucible or in a ready-made plaster form for the preparation of finished glass sculpture. Specific feature of the second case is that annealing of the finished product is carried out in the same furnace, i.e. the device is also used as annealing furnace. 3D FEM simulation model is developed, which corresponds to the specific features of the load and of the device. The aim of the study is to prove adequacy of the simulation model, using comparison between experimentally and numerically obtained results.