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1

3D Finite Element Estimation of Stray Losses in Three-Phase Transformers

Venegas Vega M. A., Escarela Perez R., Niewierowicz T.

Journal of Applied Computer Science

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2008

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Vol. 16, nr 1

89-100

EN

Stray losses and flux leakages of a three-phase three-limb transformer are determined and analyzed using 3D finite element analysis. The problem is not current driven but voltage fed. Thus, a circuit-field problem is established and solved. The operating condition analyzed is the load-loss test. Since low excitation voltages are excited during this test, the transformer works under unsaturated conditions. As a result, the transformer is modelled using a time-harmonic approach. The transformer geometry is truly three dimensional, forbidding the use of conventional 2D models. The clamp plates and transformer tank are conveniently modelled with surface impedance boundary conditions.

2

Identification and sensitivity analysis of synchronous machine d-axis parameters

Niewierowicz T., Escarela-Perez R., Campero-Littlewood E.

Journal of Applied Computer Science

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2002

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Vol. 10, nr 1

91-103

EN

A sensitivity analysis is performed to study the characteristics of the parameters of two-axis equivalent circuits (used in the modelling of solid rotor synchronous machines). The equivalent circuit parameters are determined by using a hybrid genetic algorithm, which also gives the right number of circuit damper branches that must be used to accurately reproduce the standstill frequency response of the synchronous machine. The sensitivity analysis clearly shows the relative importance of each parameter within the fitness Junction used in the identification process. Hence, it is observed that care must be taken in the identification process since the fitness function has very low sensitivity to some parameters. The results show that a sensitivity analysis of the circuit parameters could lead to a better understanding of the accepted two-axis equivalent circuits.

3

Non-linear model of the N2-laser excitation circuit

Niewierowicz T., Kawecki L., La Rosa J.

Control and Cybernetics

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2001

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Vol. 30, no 2

177-189

EN

This paper presents a non-linear model of the Blumlein circuit for the excitation of an N2-laser that leads to a high order integer-differential equation system where each of the two discharges (the spark gap and the laser chamber) taking place in the circuit are simulated by an inductance and a resistance connected in series. The inductance and the resistance of each loop are considered current dependent and their time behaviour is found by means of a parametric identification method based on the voltages measured in the charge capacitors. A comparison between two representations of the induced emf in the different loops of the circuit is used. The first one is based on the dynamical (or derivative) inductivity and the second one on the statical (or integrative) inductivity. A Gauss-Seidel algorithm for the parametric identification was used.

4

Computer aided design of dynamic analog converters of square and square root

Kawecki L., Niewierowicz T.

Journal of Applied Computer Science

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2000

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Vol. 8, nr 1

37-48

EN

This paper presents the design and computer simulation of two dynamic analog nonlinear converters: one of square and the other of square roof. These converters were registered as invention patents in the Mexican Institute of Industrial Property. The purpose of the design and simulation of the behavior of the electronic circuits in the converters are the determination of their appropriate structures for prototype elaboration and manufacture.

5

Digital model of temperature fields in electrical machines

Niewierowicz T., Kawecki L.

Journal of Applied Computer Science

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1999

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Vol. 7, nr 1

31-44

EN

The paper presents a complete variable structure mathematical model of the temperature fields inside stators and rotors of rotational electric machines that work in different modes, including the interrupted work with different relationship between the work and the rest time, and taking into account the change of temperatures of the air that circulates in the air gap. The algorithm developed mainly for a case of two - material cylindrical wall of simple geometry can also take into account different geometry of the stator and rotor. The results of investigations of temperature fields are also presented to determine the influence of the temperature changes in the air gap on the maximum temperatures inside stators and rotors. These investigations aim at establishing the optimal design of cooling systems for rotational electric machines.

6

Time and electric energy losses minimization in speed control of induction motors

Kawecki L., Niewierowicz T.

Control and Cybernetics

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1999

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Vol. 28, no 2

331-353

EN

The paper presents a method for solving the problem of the simultaneous time and electric energy losses minimization during the frequency speed control of induction motors with the electromagnetic transients. To solve this vector optimization problem, the optimization index in the form of linear combination of the scalar indexes is assumed and the Pontryagin maximum principle is used. Examples of solution for two cases of optimal frequency starting of two induction motors are presented.