Ljubljana, Slovenia
Ljubljana, Slovenia

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Stojcic B.,Kolektor ETRA | Miljavec D.,University of Ljubljana
International Journal of Electrical Power and Energy Systems | Year: 2012

The paper describes a mathematical model to be used in calculating the current distribution among the coils in the low-voltage winding of the furnace transformer. The method is derived from the leakage magnetic-field distribution in the transformer based on the minimum magnetic-field energy. The energy is calculated by using the principle of the minimum reactive power in the transformer window. The results are validated by using the finite-element model. The knowledge of the proper current distribution is very useful in designing the furnace-transformer cooling system to avoid local overheating. © 2012 Elsevier Ltd. All rights reserved.

Trbusic M.,Kolektor Etra | Cepin M.,University of Ljubljana
Elektrotehniski Vestnik/Electrotechnical Review | Year: 2011

The paper presents a method enabling calculation of the radial and serial capacitance, inductance and voltage between adjacent coils of the power transformer continuous disc winding. Definition of the equivalent electric circuit is based on the assumption of a short circuit and grounded winding next to the iron core. This way all radial capacitances are at the same time also ground capacitances. Calculation of the serial capacitance is based on the assumption of linear voltage distribution along the coil. The inductance is obtained from the stray magnetic field in the transformer window calculated in the FEMM 4.2 computer code. The equivalent circuit with respect to the 1st and 2nd Kirchhoff's law gives two systems of ordinary differential equations for the voltage and current that are solved using MATLAB calculation. Results are compared with measurement results obtained on a dry type transformer TBS (22/6.3 kV, 800 kVA, uk= 5.5 %). A comparison shows that differences between the calculated and measured values are acceptable.

Jaksic N.,Kolektor Etra
Advances in Acoustics and Vibration | Year: 2014

The paper presents phase portraits of the autonomous Duffing single-degree-of-freedom system with Coulomb dry friction in its δ - γ - ε parameter space. The considered nonlinearities of the cubic stiffness (ε) and Coulomb dry friction (γ) are widely used throughout the literature. It has been shown that there can be more than one sticking region in the phase plane. It has also been shown that an equilibrium point occurs at the critical combinations of values of the parameters γ and ε which gives rise to zero eigenvalue of the linearised system. The unstable limit cycle may appear in the case of negative viscous damping (δ); δ < 0. © 2014 Nikola Jakšić.

The optimality of the procedure of parameter identification is scrutinized in this paper. It was shown, with the relations between the mathematical theory of function approximation, three parameter probability distributions, which can adjust their shape, and the maximum-likelihood method, that the optimal expression of the distance between measured data and model fitting it can be established by using the three parameter probability distributions on the basis of iteration procedure, where the noise contained in the measured signal is extracted as well. The iterative method for optimal system/model parameter identification is presented and tested by the numerical experimentation. Four types of noise added to the simple single-degree-of-freedom system response are considered: Gauss, Cauchy, Laplace and Uniform. The method performs well for the noise types at relatively high noise content in the signal. © 2014 Elsevier Ltd.

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