Rumena Stancheva

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.

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...

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.

Data errors influence on the robustness of problem solutions

Purpose – The purpose of this paper is to evaluate the rate of discrepancy between the group of expected project results and the group of corresponding results realized preliminarily at the design stage.Design/methodology/approach – The authors formulate and solve the problem to determine the values of two assemblies of independent variables guaranteeing the project with the best (X→*) and as well this one with the worst (X→**) tolerance field of the expected Zx realization. The problem is formulated as an optimization one in nonlinear mathematical programming and it is solved by applying the flexible tolerance method.Findings – By the use of basic relations in statistical science an expression of standard deviation σZx of Zx is found and proposed. The limits in which are expected to be change in the deviations between the main project results and the corresponding ones of the implemented design, mathematically defined previous to its realization.Research limitations/implications – The accent is put on th...

Coupled Electromagnetic-Thermal Field Investigation in Induction Heating Device

The aim of the work is precise coupled –electromagnetic and temperature field analysis of an induction heating system by finite element method. Presented example is referred to real induction heating system. The problem was solved as nonlinear, transient and axisymmetrical. The numerical model of the coupled fields is based on the finite element method and electromagnetic and temperature distributions have been obtained using COMSOL 3.3 software package.