Antônio Carlos Delaiba

The effect of harmonics on power transformers loss of life

This paper is concerned with the effect of both harmonic voltage and current distortion on power transformer loss of life. The influence of possible DC current components is also taken into account. Using these non-conventional conditions superimposed upon the fundamental frequency operation, the overall thermal conditions and loss of life are estimated using frequency domain techniques.

A comparative investigation of electromechanical stresses on transformers caused by inrush and short-circuit currents

This paper presents the mechanical effect on transformers when subjected to one of the power quality indicators, i.e., the electromagnetic transients. A common reason for internal faults in transformers windings is the weak insulation. This effect can be caused and accelerated by the electromechanical efforts produced by the inrush and short-circuit currents. Even though the transformer energizing is considered a normal operation, it produces high currents and this phenomenon significantly reduces the transformer life expectancy and may even lead to its instantaneous or timing destruction. Moreover, taking into account the same magnitude of current, the inrush currents can produce greater forces than those caused by short-circuit currents. Therefore, this papers aims to present and compare the electromechanical effects produced by the inrush and short-circuit currents in the transformers windings. To conduct this research, FLUX software in its 3D version, based on the finite element method (FEM) will be used. To highlight the overall model and the software performance, a laboratory 15 kVA transformer is utilized. It has been built with concentric double-layer windings and ferromagnetic core with three columns.

Behavior of three-phase transformers supplying non linear loads using time domain representation and finite element analysis

This paper aims to present and discuss the magnetic and electrical results derived from three-phase power transformers modeling under nonlinear load conditions. The approach uses time-domain techniques and the finite element method. The transformer internal electromagnetic equations and the external equivalent circuit are simultaneously solved through a well-established computational package. The nonlinear load is a 6-pulse rectifier supplied by a nonlinear modeled power transformer. The waveform for different currents and voltages, as well as the flux line distribution are given and fully described. The results obtained from the simulation are compared to experimental tests.

Electronic equipment dielectric and thermal withstand capability curves for refunding analysis purposes

This paper is aimed at obtaining dielectric and thermal withstand capability curves of electronic devices in order to demonstrate the allowable voltage and current effect limits. The idea is to establish a computational procedure to compare system voltage and current disturbances with the equipment tolerance permitted values to guarantee the physical integrality of the product. To highlight the methodology, new and second hand TV, stereo, personal computer units are experimentally driven to their extreme dielectric and thermal strengths. The results are then referred as tolerance curves which are used as guidelines for the computational analysis of the consistency of a given relationship between a system occurrence and the consumer claimed damage for a specific product. The applicability of the whole process can be justified by the growing interest in the establishment of systematic procedures, based on well accepted computational simulations, yielding final reports that provide the necessary answer to the refunding process demand.

Energy billing under nonsinusoidal conditions

This paper aims to present a new point of view about the active power measurement, for billing purposes, measured at the Point of Common Coupling (PCC) between the utility and the consumer when harmonic distortions are involved. Depending on the origin of it, the active power can result in higher or lower values in comparison to the fundamental component. The consequences are higher costs for the consumer or losses for the utility. Using computational simulations and theoretical analysis, these aspects are evaluated and compared.

Procedimentos de análise de eficiência energética em sistemas de ar comprimido industriais

Os sistemas de ar comprimido representam parcela expressiva do consumo energético de uma instalação industrial. Porém, o uso e manutenção inadequada provocam redução no desempenho global caracterizando uma fonte constante de desperdícios. Dessa forma, este trabalho se encontra direcionado para o desenvolvimento e comprovação de técnicas para análise da eficiência energética de sistemas de ar comprimido. A análise será realizada no compressor instalado no laboratório de sistemas motrizes da Faculdade de Engenharia Elétrica da UFU. Dentro deste foco principal, as atividades desenvolvidas e apresentadas neste documento contemplam questões associadas com a conservação de energia, apresentação do protótipo, metodologia de diagnóstico energético, e por fim, um estudo de caso obtido do protótipo com respectiva análise econômica de investimentos.

Practical validation for the frequency domain approach to study the thermal behavior of transformers under nonsinusoidal operation conditions

This paper is focused in the direction of practical and theoretical aspects of thermal performance of transformers under distorted operating conditions. Using the superposition method, the thermal conditions are estimated through the frequency domain technique. To validate the theoretical results, practical measurements are made using a 15 kVA transformer prototype supplying a 6 pulse rectifier. The results are then used to validate the proposed method to investigate transformer thermal behavior.