Magnetic vector potential and magnetic field intensity due to a finite current carrying cylinder considering a variable current density along its axial dimension

With the aim of introducing a computationally efficient solution for problems such as the fast computation of magnetic field magnitudes and forces in coils and windings, this paper presents analytical expressions for the magnetic vector potential and magnetic field intensity in radial and axial directions due to a finite cylinder with infinitesimal wall thickness carrying a linearly varying current density between the values at the lower and upper ends. All expressions have been derived in terms of complete elliptic integrals of first, second and third kind, whose evaluation is achieved by means of very fast algorithms. The formulas presented make possible the fast computation of magnetic field at any point in space at reduced computational cost. The formulation is not only specially suited for modeling the current distribution in foil windings of power transformers but also for representing the magnetization of transformer core legs. The present method is also useful for efficient modeling of cylinders with constant current density since it is a generalization of this especial case. Finally, an example is presented where the results achieved using the proposed method are compared with those obtained using the finite element method showing a very good agreement between them.Fil: Díaz, Guillermo A.. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; ArgentinaFil: Mombello, Enrique Esteban. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Stephan, Voss. No especifíca

Expert system for the assessment of power transformer insulation condition based on type-2 fuzzy logic systems

An efficient expert system for the power transformer condition assessment is presented in this paper. Through the application of Duval's triangle and the method of the gas ratios a first assessment of the transformer condition is obtained in the form of a dissolved gas analysis (DGA) diagnosis according IEC 60599. As a second step, a knowledge mining procedure is performed, by conducting surveys whose results are fed into a first Type-2 Fuzzy Logic System (T2-FLS), in order to initially evaluate the condition of the equipment taking only the results of dissolved gas analysis into account. The output of this first T2-FLS is used as the input of a second T2-FLS, which additionally weighs up the condition of the paper-oil system. The output of this last T2-FLS is given in terms of words easily understandable by the maintenance personnel. The proposed assessing methodology has been validated for several cases of transformers in service. © 2011 Elsevier Ltd. All rights reserved.Fil: Flores, Wilfredo C.. Universidad Nacional Autónoma de Honduras; Honduras. Universidad Nacional de San Juan; ArgentinaFil: Mombello, Enrique Esteban. Universidad Nacional de San Juan; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Jardini, José. A.. Universidade de Sao Paulo; BrasilFil: Rattá Gutiérrez, Giuseppe Aníbal. Universidad Nacional de San Juan; ArgentinaFil: Corvo, Antonio M.. Companhia de Transmissão de Energía Elétrica Paulista; Brasi

New Compact White-Box Transformer Model for the Calculation of Electromagnetic Transients

In a recent work, a successful power transformer white-box model for the calculation of electromagnetic transients has been presented. Although this model gives very satisfactory results, when applied to large transformers it requires a large number of auxiliary loops to model the damping. This can be problematic as it not only requires more computational effort, but the size of the input data may even preclude its use with ATP-EMTP and perhaps with other EMTP-based software that have limitations in this regard. In this work a new reduced model which enables its use with ATP-EMTP is presented. This model requires a much smaller number of circuit components than the original model, which allows the data size and simulation time to be substantially reduced without practically affecting the calculation results. This has been achieved through the reduction of the rank of the sub-matrices that characterize the inductive coupling between the main winding sections and the auxiliary loops used to model the damping. The new model has been validated by making comparisons of the frequency responses calculated using the new compact model with the ones calculated with the original model developed for the case study used by the CIGRE JWG A2/C4.52 to test the accuracy of various types of transformer models.Fil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentin

Impedances for the calculation of electromagnetic transient phenomena and resonance in transformer windings

In this paper the authors look for a better understanding of the properties of the impedances of transformer windings. These impedances are very important for the calculation of the resonant behavior of transformers. The research is focused in the influence of the iron and copper losses on the winding resistances. An important measurement work on many transformer windings in the frequency domain made possible to draw conclusions about the behavior of the magnetic field and the representation of the losses in a circuit model.Fil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; ArgentinaFil: Möller, Klaus. Institut für Allgemeine Elektrotechnik und Hochspannungstechnik; Alemani

New SFRA measurement interpretation methodology for the diagnosis of power transformers

The analysis of the frequency response by the Sweep Frequency Response Analysis method (SFRA) is a diagnosis technique that can detect displacements, deformations and other mechanical and electrical failures in power and distribution transformers. One of the main disadvantages of the method is the lack of an international agreement regarding the methodology for measurement analysis, which is usually done by experts in the field, who normally make the diagnosis with the aid of statistical parameters such as correlation coefficient and standard deviation, or parameters derived from modeling the frequency response as a complex transfer function, represented by poles and zeros, or poles and residues. This paper presents a new methodology for SFRA measurement analysis, which makes use of the properties of various types of parameters and expert knowledge through the application of fuzzy causal diagnosis.Fil: Secue, Janneth R.. Ingetec S.A. Ingenieros Consultores; ColombiaFil: Mombello, Enrique Esteban. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Fault Interpretation Algorithm Using Frequency-Response Analysis of Power Transformers

Sweep frequency-response analysis (SFRA) is a powerful technique to detect mechanical damage in transformer windings, such as deformations and displacements, as well as other failures, helping to prevent severe damage. Since SFRA is a sensitive diagnostic technique, there are these days several commercially available measurement instruments to perform the tests, but the failure interpretation is usually based on expert opinion. One of the most advisable ways to face the task of interpretation of SFRA test results is the use of mathematical indices to detect abnormalities along with an interpretation scheme. The failure interpretation methodology of SFRA tests must establish the possible relationships between frequency ranges and specific failures, because different failure types can be detected in different frequency ranges of the SFRA trace. This paper proposes a new methodology for power transformer failure diagnosis using the relationships between the different decomposition levels of the original trace obtained with the use of the discrete wavelet transform and the definition of frequency regions with variable limits, according to the shape of the trace. Moreover, an interpretation map and a vector fitting analysis are also proposed in order to establish a specific failure.Fil: Gonzales Arispe, Jimmy Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; ArgentinaFil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentin

Power Transformer Diagnosis Using FRA and Fuzzy Sets

This paper presents a novel method for failure detection and interpretation in power transformers using Frequency Response Analysis (FRA). Mathematical indexes are used for failure detection. The performance of the most used mathematical indexes is evaluated and the most sensitive for frequency response analysis is selected. An approach based on a suitable codification of response frequency bands is proposed for failure classification. A novel characteristic of this work is the application of Fuzzy Sets to represent the mathematical index limits for failure detection. The proposed method has been validated using two different case studies, and the diagnosis results obtained for them show a good agreement with the real failures.Fil: González Arispe, Jimmy C.. Universidad Nacional de San Juan; ArgentinaFil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Energia Electrica; Argentina. Universidad Nacional de San Juan; Argentin

Magnetic field due to a finite current carrying disk considering a vari able current density along its radial dimension

This paper proposes a fast and accurate methodology to calculate the magnetic field produced by a finite disk considering a linear variation of the current density between the inner and the outer radius. The mathematical expressions have been developed with the aim of reducing the computational effort, while ensuring accurate and reliable results. Additionally, the strategies presented in this work provide expressions which are free of singularities.Fil: Díaz Florez, Guillermo A.. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energia Eléctrica; ArgentinaFil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energia Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energia Eléctrica; Argentin

Semianalytic Integral Method (SAIM) for Fast Solution of Current Distribution in Foil Winding Transformers

A novel mesh-free axisymmetric methodology for the determination of the low-frequency current distribution in foil windings is presented in this paper. The proposed methodology applies equivalent models for the foil winding and the iron core, which are based on the field produced by elementary geometric configurations and boundary conditions derived from Maxwell's equations. Power losses in the windings due to skin effect and proximity effect are calculated with the proposed method and the finite-element method (FEM). The comparison of both results showed excellent agreement. The computational performance is also compared with FEM. It has been found that the proposed method achieves significant improvements in computational times compared with FEM retaining the level of precision required for transformer design purposes.Fil: Díaz Florez, Guillermo A.. Universidad de La Salle; ColombiaFil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentin

Detection of Failures Within Transformers by FRA Using Multiresolution Decomposition

The detection of failures within power transformers is considered an important issue since these components are of critical importance for power system reliability; moreover, their replacement cost is extremely high. In monitoring the transformer condition along its useful life, frequency-response analysis (FRA) has gained great interest due to its sensitivity to failures in the windings and the iron core. These failures can be detected by evaluating transfer function changes by means of statistical and mathematical indices and classified according the frequency band in which these changes take place. However, this procedure involves evaluation inaccuracies due to disturbances or minor changes during FRA measurements. The new methodology is based on the decomposition of the original responses in several levels of decomposition (filtering) using the discrete wavelet transform, and the subsequent comparison using smooth versions of the responses. Fault detection is further supported with statistical indices calculated using the frequency band where abnormal differences appear. This procedure gives more robustness to the method and reduces the possible influence of disturbances during measurement in the diagnosis result. The methodology has been tested using different failure cases and two of them are used for validation purposes in this paper.Fil: González Arispe, Jimmy Cesar. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina. Deutscher Akademischer Austauschdiest ; AlemaniaFil: Mombello, Enrique Esteban. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin