Juan C Olivares-Galvan | Universidad Autónoma Metropolitana-Azcapotzalco (original) (raw)

Papers by Juan C Olivares-Galvan

—In this paper, a Multi Scale Recurrence Quantification Analysis (MSRQA) method is proposed to cl... more —In this paper, a Multi Scale Recurrence Quantification Analysis (MSRQA) method is proposed to clustering harmonics on microgrid systems. MSRQA is composed by the Variational Mode Decomposition algorithm and the Recurrence Quantification Analysis (RQA). MSRQA decomposes a signal into a finite number of Mono-Component Signals (MCSs), then a feature extraction is carry out by the RQA on each MCS. Finally, the identification of the optimal number of clusters based on the features extracted by RQA and the Davies-Bouldin index is carry out on the monitored microgrid system test signals. At the end an index based on the cluster information and the RQA measure is proposed to identify the harmonics present on the dynamic system behavior. Keywords— Clustering Harmonic Analysis, Feature Extraction, Microgrid, Multi Scale Recurrence Quantification Analysis (MRQA), Variational Mode Decomposition (VMD).

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— The modern world is moving towards the smart grids and increased use of electronic loads. The r... more — The modern world is moving towards the smart grids and increased use of electronic loads. The realization of smart grid technology is the increased use of distributed energy resources, introducing new intelligent, communication and control systems that are mostly electronic circuits. The issues associated with this technology are bi-directional flow of power flow, increased harmonic emissions, direct current offsets and unbalances, voltage variation and switching transients. The increased usage of electronic loads at distribution level are generating harmonics, which in turn increases power losses in the transformers and cause premature damage. These loads mostly inject the odd harmonics in the distribution system, resulting in the temperature rise of the transformer. It causes accelerated aging of transformer thereby called the attention of manufacturers and researchers to develop the procedures for enhancing the system reliability. In the literature, several methods have been proposed for calculating losses and derating the transformer such as experimental, IEEE recommended, analytical and Finite Element Method (FEM). This paper reviews the finite element analysis of distribution transformer under harmonics condition. The losses associated with harmonics, modeling and derating of transformer are the topics included in this paper. It is found that the main focus is paid on derating and losses calculation of the transformer for a percentage of harmonic contents.

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— Today, transformers are basic elements and of great importance in electrical systems. Unfortuna... more — Today, transformers are basic elements and of great importance in electrical systems. Unfortunately, they are prone to failures, including short-circuit failures. Therefore, it is necessary to apply methodologies that help to detect faults in a timely manner to avoid damage to the transformer. In this paper, it is proposed a new methodology to identify short-circuit faults by means of a technique called Empirical Mode Decomposition (EMD), which decomposes the signals into new signals called Intrinsic Mode Functions (IMFs). These signals are analyzed with the entropy of Shannon in order to obtain indices that help to characterize the severity of the fault. The analyzed signals correspond to both a healthy condition and different short-circuited conditions, i.e., 10, 20, 30, and 40 turns. Results demonstrate the effectiveness of the proposal.

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Resumen En este trabajo de investigación, la celda de combustible de óxido sólido (SOFC), con una... more Resumen En este trabajo de investigación, la celda de combustible de óxido sólido (SOFC), con una potencia nominal de 50 kW, está conectada con el inversor de voltaje (VSI) y la técnica de conmutación aplicada al control de corriente de histéresis. Los controladores Estándar del Modelo Aditivo (SAM) Neuro-Fuzzy y PI se emplean por separado para controlar la demanda de potencia activa y reactiva de la red. La potencia real y la potencia reactiva se controlan mediante la manipulación de las corrientes de los ejes d y q, respectivamente. Se encontró que tanto Neuro-Fuzzy como los controladores PI son capaces de controlar la demanda de potencia activa y reactiva de la red, pero la primera sustituye a la última. La tensión de salida y las formas de onda de corriente del inversor se simulan para suavizarlas y hacerlas deseables para el acoplamiento con la red. La estrategia de control desacopla la potencia real y reactiva y asegura su flujo independiente en la red. Toda la configuración se simula en MATLAB / Simulink. Abstract In this research paper, a Solid Oxide Fuel Cell (SOFC), rated at 50 kW, is interfaced with grid through Voltage Source Inverter (VSI) and switching technique applied is Hysteresis Current Control. Standard Additive Model (SAM) based Neuro-Fuzzy and PI controllers are separately employed to control the Active and Reactive power demand of grid. The real and reactive powers are controlled by the manipulation of d and q axis currents, respectively. It was found that both Neuro-Fuzzy and PI controllers are capable in controlling the demand Active and Reactive powers of grid but the former supersede the latter. The output voltage and current waveforms of the inverter are simulated for smoothness in order to make it desirable for coupling with the grid. The control strategy decouples the real and reactive power and ensures their independent flow in the grid. The whole setup is simulated in MATLAB/Simulink.

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—A formulation based on 2D Cartesian and axisymmetric finite-element (FE) models, modified nodal ... more —A formulation based on 2D Cartesian and axisymmetric finite-element (FE) models, modified nodal analysis (MNA) and a multi-field system approach is proposed to analyze a three-phase power transformer. Interesting capabilities are thus achieved, overcoming the difficulties naturally arising with 3D simulations: high computational times and memory demand. A 2D Cartesian FE model is employed to represent the main cross section of the transformer. An axisymmetric representation is used for the end sections of each set of windings. All models are simultaneously solved, providing a powerful method that is easy to implement at low computational costs. We present preliminary simulation results that show that our proposal is sound.

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— This paper presents an experimental and numerical analysis regarding shorted electrical steel l... more — This paper presents an experimental and numerical analysis regarding shorted electrical steel laminations of core of a small transformer core (120 VA single-phase shell-type transformer). Experimental tests were performed to measure the core losses of the transformer with and without shorted electrical steel laminations. Soft solder was utilized to produce the shorted region in the transformer core. Furthermore, 3-D Finite Element (FE) simulations were carried out to compute the eddy current losses in the core of transformer with shorted electrical steel laminations. The laminations of the core and their insulation were taken into account in the transformer model. Finally, several FE simulations were performed to calculate the eddy current losses for several cases, where the location and size of the shorted lamination region was varied in the core of transformer.

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Inrush current has been well-studied in transformers using different methods to diagnose internal... more Inrush current has been well-studied in transformers using different methods to diagnose internal faults. In this paper, a new methodology is proposed using experimental data for obtaining a time-model based on inrush currents. The main contribution of this paper consists of providing a model that accurately reproduces the inrush and steady state currents of single-phase transformers, offering the unique ability to analyze several severity levels of turn to turn faults. The obtained model considers eleven cases of inter-turn fault (2, 3, 4, 5, 10, 15, 20, 25, 30, 35, and 40 short-circuited turns) and allows the study of indices to detect inter-turn faults. The proposed model is based on two functions: a steady-state function based on Fourier series and a residual transient function based on a sum of Gaussian functions. The model allows the study of harmonic content because of its direct time-frequency representation. The model is developed using experimental signals measured from a single-phase transformer, which is validated by means of error criteria that assesses experimental and modeled signals. Its capability to reproduce non-modeled signals with different inter-turn fault cases is also evaluated. The modeling of these signals can be a useful tool for simulation-based applications where a reliable waveform reproduction is needed. On the other hand, indices such as total harmonic distortion, energy spectral density and second harmonic ratio are obtained from the proposed model to study its behavior, depending on the severity of the inter-turn faults. Results demonstrate its usefulness to characterize the level of fault severity.

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A new formula is developed for the surface impedance of a nonlinear magnetic conductive semi-infi... more A new formula is developed for the surface impedance of a nonlinear magnetic conductive semi-infinite slab. The impedance expression allows for proper incorporation of the nonlinear characteristic of the magnetic material, also using an analytical expression. Thus, the usual step representation of the B–H curve is superseded. Normal and tangential magnetic components may simultaneously exist, avoiding the classical premise that only the tangential component exists. This way, it is possible to represent highly magnetic permeable materials where the normal component of the magnetic field is the main one. Our analytical formulation and solution can be for example used for calculation of losses in electrical machines or along with FE software code to avoid meshing of magnetic conductive regions. Index Terms— Magnetic flux penetration, nonlinear magnetic field, nonlinear permeability, surface impedance.

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A strong circuit-field coupling technique that can analyze multiple magnetic field systems (2-D C... more A strong circuit-field coupling technique that can analyze multiple magnetic field systems (2-D Cartesian and axisymmetric) is adapted to study power transformers. The technique is based on finite-element (FE) and modified nodal analyses, leading to a multi-field system approach that can effectively take account of the 3-D magnetic field existing inside and outside the transformer core. Hence, cumbersome 3-D FE simulations are circumvented, overcoming high computational costs. A 2-D Cartesian FE model is set up to represent the cross section of the transformer core and its three-phase winding, whereas an axisymmetric representation is employed for the end sections of each set of windings (one per phase). All models and their associated circuit systems are simultaneously solved, providing a circuit-field method that is easy to implement at low computational cost, keeping the well-known advantages of 2-D FE modeling. Electrical currents and local values of magnetic flux density are calculated for two limiting conditions: rated load and short-circuit operation. Our approach shows a remarkably small difference (no higher than 1%) with a full 3-D FE model. Index Terms— End-winding effects, finite-element (FE) analysis, power transformer, short-circuit condition, strong coupling method.

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A B S T R A C T The application of signal processing techniques is a fundamental step for fault d... more A B S T R A C T The application of signal processing techniques is a fundamental step for fault diagnostic methodologies. The application of empirical mode decomposition (EMD)-based methods such as classic EMD, ensemble EMD (EEMD), and complete EEMD (CEEMD) is presented in this work for the analysis of inrush current signals. This analysis leads to the detection of short-circuited turns in transformers. Results show that CEEMD provides the best performance, as it readily extracts the information related to the fault, requiring of acceptable computational resources. Actual inrush current signals of a transformer with short-circuited turns are also considered. The number of short-circuited turns ranges from 5 to 40. Useful indices, such as the Shannon Entropy, Energy, and root-mean-square value, are obtained from the information provided by the CEEMD approach. These indices are analyzed for both the transient state and the steady state of the current signals, providing the proper quantification of the fault severity.

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Analysis based on application of two-parametric Weibull distribution is commonly used to characte... more Analysis based on application of two-parametric Weibull distribution is commonly used to characterize power equipment life distributions in the presence of censored data. Numerous studies have focused on enhancing the accuracy of statistical parameter estimation. However, there is still no straightforward and rigorous analytical method of estimation of the Weibull parameters and the mean life. In this work, a new method for mean life evaluation of power system equipment, based on the two-parameter Weibull distribution, is presented for complete and right-censored failure data. Classical maximum likelihood estimation (MLE) is employed for determination of distribution parameters. However, an estimator based on asymptotic expansions is proposed, overpassing the disadvantages of MLE-based methods that employ numerical or graphical techniques. High accuracy of the proposed method with respect to other estimators is also shown by analyzing two right-censored lifetime data sets with different sample sizes for three types of power equipment. The efficiency and accuracy of the proposed analytical method find their strengths in the analytically obtained closed-form expressions for the distribution parameters.

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—In large power transformers, the presence of stray currents in the structural elements near the ... more —In large power transformers, the presence of stray currents in the structural elements near the high current bush-ings can be considerable, and this leads to hot spots. This work presents a practical analysis of overheating in the bolts that join the tank and the cover, which are near the high current bush-ings of the transformer. Overheating results are analyzed and discussed for the case of a 420-MVA transformer. The hot spots in the flange–bolt regions are discovered by thermal maps that are obtained during power transformer operation as a part of a preventive maintenance program. In this paper, we use copper links to ensure the connection of both the cover and tank body, significantly reducing the overheating of the flange–bolt region. The copper link solution has been validated by measurements. We have used calibrated measurement instruments in all the experiments. Moreover, a 3-D finite-element analysis of the geometry of interest has been used to verify the copper link solution.

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High impedance faults are difficult to detect by conventional overcurrent relays mainly because o... more High impedance faults are difficult to detect by conventional overcurrent relays mainly because of their
low current magnitudes. This paper describes a model for representing high impedance faults in electrical
distribution systems. The model is based in a non-linear resistance representing the high impedance path
during this kind of faults. Based on this model, the performance of several electric variables associated to
high impedance faults is analyzed and an algorithm for high impedance fault detection in electrical distribution
systems is presented. Field measurement and computer simulations validate the high impedance
fault model and the proposed fault detection algorithm.

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This work is concerned with the study of the asymmetrical phenomenon observed in three-phase tran... more This work is concerned with the study of the asymmetrical phenomenon observed in three-phase transformers during the standard short-circuit test. The purpose of our work is to see if the asymmetric measurements can be predicted with the use of 2D finite-element models. To this end, we ...

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Page 1. Calculation of the Magnetic Field Intensity in a Rectangular Conductor Carrying Current i... more Page 1. Calculation of the Magnetic Field Intensity in a Rectangular Conductor Carrying Current in Electromagnetism Introductory Courses Juan C. Olivares-Galván1*, Iván Hernández2 , Pavlos S. Georgilakis 3, Eduardo Campero-Littlewood1 ...

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