Asymmetrical magnetization in three-phase core type transformers

The performance of the three-phase core type transformers, under AC/DC double excitation is discussed in this work. It is presented a mathematical model that considers the mutual coupling between phases and the magnetic nonlinearity. The validity of the proposed model is verified by means of the experimental and simulated results.

A neural approach to evaluate the effect of lightning in power transformers

This paper proposes the application of computational intelligence techniques to assist complex problems concerning lightning in transformers. In order to estimate the currents related to lightning in a transformer, a neural tool is presented. ATP has generated the training vectors. The input variables used in Artificial Neural Networks (ANN) were the wave front time, the wave tail time, the voltage variation rate and the output variable is the maximum current in the secondary of the transformer. These parameters can define the behavior and severity of lightning. Based on these concepts and from the results obtained, it can be verified that the overvoltages at the secondary of transformer are also affected by the discharge waveform in a similar way to the primary side. By using the tool developed, the high voltage process in the distribution transformers can be mapped and estimated with more precision aiding the transformer project process, minimizing empirics and evaluation errors, and contributing to minimize the failure rate of transformers. © 2009 The Berkeley Electronic Press. All rights reserved.

The use of current transformers for noise detection due to sparking in insulators strings in high voltage transmission lines

In a general way, in an electric power utility the current transformers (CT) are used to measurement and protection of transmission lines (TL) 1 The Power Line Carriers systems (PLC) are used for communication between electrical substations and transmission line protection. However, with the increasing use of optical fiber to communication (due mainly to its high data transmission rate and low signal-noise relation) this application loses potentiality. Therefore, other functions must be defined to equipments that are still in using, one of them is detecting faults (short-circuits) and transmission lines insulator strings damages 2. The purpose of this paper is to verify the possibility of using the path to the ground offered by the CTs instead of capacitive couplings / capacitive potential transformers to detect damaged insulators, since the current transformers are always present in all transmission lines (TL's) bays. To this a comparison between this new proposal and the PLC previous proposed system 2 is shown, evaluating the economical and technical points of view. ©2010 IEEE.

Transmission network expansion planning considering phase-shifter transformers

This paper presents a novel mathematical model for the transmission network expansion planning problem. Main idea is to consider phase-shifter (PS) transformers as a new element of the transmission system expansion together with other traditional components such as transmission lines and conventional transformers. In this way, PS are added in order to redistribute active power flows in the system and, consequently, to diminish the total investment costs due to new transmission lines. Proposed mathematical model presents the structure of a mixed-integer nonlinear programming (MINLP) problem and is based on the standard DC model. In this paper, there is also applied a specialized genetic algorithm aimed at optimizing the allocation of candidate components in the network. Results obtained from computational simulations carried out with IEEE-24 bus system show an outstanding performance of the proposed methodology and model, indicating the technical viability of using these nonconventional devices during the planning process. Copyright © 2012 Celso T. Miasaki et al.

Fast fault diagnosis in power transformers using optimum-path forest

In this paper we propose a fast and an accurate method for fault diagnosis in power transformers by means of Optimum-Path Forest (OPF) classifier. Since we applied Dissolved Gas Analysis (DGA), the samples have been labeled by IEEE/IEC standard, which was further analyzed by OPF and several other well known supervised pattern recognition techniques. The experiments have showed that OPF can achieve high recognition rates with low computational cost. © 2012 IEEE.

A new design methodology for multipulse rectifiers with Delta auto-connected transformers and a retrofit application in Adjustable Speed Drives (ASDs)

Multipulse rectifiers can replace a conventional six pulse three-phase rectifier (diode bridge) providing a DC voltage with low ripple, low Total Harmonic Distortion of current (THDi) and a high Power Factor (PF). In this context is presented a multipulse rectifier with generalized Delta-differential autotransformer topology, which can provide any level of DC output voltage for any level of three-phase AC input voltage. This paper presents all the possible configurations for Delta topology in order to choose, through graphics, one configuration that presents reduced weight and volume. The average voltage on the DC bus must be compatible with the DC voltage in the six pulse rectifier used in commercial ASDs. Therefore, it is possible to apply the retrofit technique to replace the conventional bridge rectifier by the proposed multipulse rectifier. Based on mathematic models and simulation results, an 18-pulse rectifier with Delta topology, 220 V of line voltage, 315 V of DC output, and rating 2.5 kW of power was designed, implemented and applied for three different commercial ASDs. Experimental results as voltage and current waveforms and results about PF and THDi will be presented. © 2012 IEEE.

The application of neural networks to the analysis of dissolved gases in insulating oil used in transformers

The state of insulating oils used in transformers is determined through the accomplishment of physical-chemical tests, which determine the state of the oil, as well as the chromatography test, which determines possible faults in the equipment. This article concentrate on determining, from a new methodology, a relationship among the variation of the indices obtained from the physical-chemical tests with those indices supplied by the chromatography tests.The determination of the relationship among the tests is accomplished through the application of neural networks. From the data obtained by physical-chemical tests, the network is capable to determine the relationship among the concentration of the main gases present in a certain sample, which were detected by the chromatography tests.More specifically, the proposed approach uses neural networks of perceptron type constituted of multiple layers. After the process of network training, it is possible to determine the existent relationship between the physical-chemical tests and the amount of gases present in the insulating oil.

Influence of double excitation AC/DC in the reactive power demand of 3-phase transformers

In this work it is discussed the performance of the reactive power demand in three-leg transformer core and three-phase transformer bank, under different conditions of AC/DC double excitation. In order to analyse the influence of double excitation in reactive power theoretically a mathematical model was developed considering the mutual coupling between phases and the magnetic nonlinearity. The validity of the proposed model is verified by means of the experimental and simulated results.

Partial Discharge Phenomena in Converter and Traction Transformers: Identification and Reliability

After the development of power electronics converters, the number of transformers subjected to non-sinusoidal stresses (including DC) has increased in applications such as HVDC links and traction (electric train power cars). The effects of non-sinusoidal voltages on transformer insulation have been investigated by many researchers, but still now, there are some issues that must be understood. Some of those issues are tackled in this Thesis, studying PD phenomena behavior in Kraft paper, pressboard and mineral oil at different voltage conditions like AC, DC, AC+DC, notched AC and square waveforms. From the point of view of converter transformers, it was found that the combined effect of AC and DC voltages produces higher stresses in the pressboard that those that are present under pure DC voltages. The electrical conductivity of the dielectric systems in DC and AC+DC conditions has demonstrated to be a critical parameter, so, its measurement and analysis was also taken into account during all the experiments. Regarding notched voltages, the RMS reduction caused by notches (depending on firing and overlap angles) seems to increase the PDIV. However, the experimental results show that once PD activity has incepted, the notches increase PD repetition rate and magnitude, producing a higher degradation rate of paper. On the other hand, the reduction of mineral oil stocks, their relatively low flash point as well as environmental issues, are factors that are pushing towards the use of esters as transformer insulating fluids. This PhD Thesis also covers the study of two different esters with the scope to validate their use in traction transformers. Mineral oil was used as benchmark. The complete set of dielectric tests performed in the three fluids, show that esters behave better than mineral oil in practically all the investigated conditions, so, their application in traction transformers is possible and encouraged.

Narrativa argentina reciente : los muchachos de ahora juegan con Transformers

La novela de Roberto Arlt, El juguete rabioso (1926), pone en marcha a la narrativa del siglo XX en los estertores del período celebratorio del Centenario y abre una genealogía en la literatura argentina identificada con lo que José Amícola define como una "escritura de la exageración" y con una narrativa de cuño netamente urbano. Las dinámicas que se perciben en la narrativa actual, con toda la savia aportada por los medios masivos de comunicación y la cultura de masas, remiten a otro tipo de imaginarios que incluyen a la técnica como elemento configurador e inseparable de la percepción de los eventos narrados. El Bicentenario se inaugura con una narrativa que sigue siendo vital y no pierde su aptitud novelesca, hereditaria de la tradición de la novela de aventuras, del folletín, pero a su vez atravesada por una estética aun más violenta y paródica. Cómo se inserta en la tradición abierta por Arlt y qué elementos se exacerban en un contexto tan conflictivo como el del principio del milenio, es lo que será analizado en dos novelas recientes, Los topos (2008) de Félix Bruzzone y Letra muerta (2009) de Mariano García.

Narrativa argentina reciente : los muchachos de ahora juegan con Transformers

La novela de Roberto Arlt, El juguete rabioso (1926), pone en marcha a la narrativa del siglo XX en los estertores del período celebratorio del Centenario y abre una genealogía en la literatura argentina identificada con lo que José Amícola define como una "escritura de la exageración" y con una narrativa de cuño netamente urbano. Las dinámicas que se perciben en la narrativa actual, con toda la savia aportada por los medios masivos de comunicación y la cultura de masas, remiten a otro tipo de imaginarios que incluyen a la técnica como elemento configurador e inseparable de la percepción de los eventos narrados. El Bicentenario se inaugura con una narrativa que sigue siendo vital y no pierde su aptitud novelesca, hereditaria de la tradición de la novela de aventuras, del folletín, pero a su vez atravesada por una estética aun más violenta y paródica. Cómo se inserta en la tradición abierta por Arlt y qué elementos se exacerban en un contexto tan conflictivo como el del principio del milenio, es lo que será analizado en dos novelas recientes, Los topos (2008) de Félix Bruzzone y Letra muerta (2009) de Mariano García.

Narrativa argentina reciente : los muchachos de ahora juegan con Transformers

La novela de Roberto Arlt, El juguete rabioso (1926), pone en marcha a la narrativa del siglo XX en los estertores del período celebratorio del Centenario y abre una genealogía en la literatura argentina identificada con lo que José Amícola define como una "escritura de la exageración" y con una narrativa de cuño netamente urbano. Las dinámicas que se perciben en la narrativa actual, con toda la savia aportada por los medios masivos de comunicación y la cultura de masas, remiten a otro tipo de imaginarios que incluyen a la técnica como elemento configurador e inseparable de la percepción de los eventos narrados. El Bicentenario se inaugura con una narrativa que sigue siendo vital y no pierde su aptitud novelesca, hereditaria de la tradición de la novela de aventuras, del folletín, pero a su vez atravesada por una estética aun más violenta y paródica. Cómo se inserta en la tradición abierta por Arlt y qué elementos se exacerban en un contexto tan conflictivo como el del principio del milenio, es lo que será analizado en dos novelas recientes, Los topos (2008) de Félix Bruzzone y Letra muerta (2009) de Mariano García.