DIE - DIAMAT - Artículos de Revistas

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About the difference between zero-sequence magnetizing impedances of a 3-phase core-type transformer
(Elsevier, 2014-11-01) Sorrentino, Elmer; Burgos Díaz, Juan Carlos
This paper analyzes the difference between zero-sequence magnetizing impedances (Z(0M)) of a 3-phase core-type transformer. Z(0M) in per-unit is smaller for an external winding than foran internal winding. The difference between both Z(0M) values is similar to the positive-sequence short-circuit impedance between both windings for units without magnetic shunts on the tank wall as well as for units without tank. This fact can be observed in measured values, and in the results of 3D models. However, the results of simple 2D models do not show this behavior; therefore, this paper demonstrates that this fact only can be explained from 3D models. The results are shown for different cases: transformers with and without magnetic shunts on the tank wall, and transformers without tank. In transformers with magnetic shunts on the tank wall, or in magnetostatic simulations of transformers with tank, the difference between both Z(0M) values is not very similar to the positive-sequence short-circuit impedance between both windings.
Application of 2D linear modeling for computing zero-sequence short-circuit impedances of 3-phase core-type YNynd transformers
(Elsevier, 2015-05-01) Sorrentino, Elmer; Burgos Díaz, Juan Carlos
This paper shows the application of 2D linear modeling for computing zero-sequence short-circuit impedances (Z(osc)) of 3-phase core-type YNynd transformers. Firstly, a basic description of these impedances is shown. The proposed 2D model is based on two steps: (a) the search of the currents to satisfy the condition of induced voltage equal to zero in short-circuited windings; (b) the use of constants (K-x and K-p) to approximate 2D results to results of real 3D geometries. K-x is related to the computed reactances, and K-p is related to the computed values for the power losses during Z(osc) tests. Induced currents in short-circuited windings are found by an iterative process, in order to apply constant current densities in the model of each winding. Results of the model are accurate in comparison with measured values in five transformers. Tertiary is the innermost winding in four units, and the outermost winding in one unit. Open-delta cases and closed-delta cases are considered, as well as cases with and without magnetic shunts on the tank walls. Equivalent permeability of tank steel has an influence on results but a reasonable accuracy is obtained with an intermediate value of this parameter; thus, non-linearity is not a concern in this case. A good accuracy is also obtained for a wide range of K-x and K-p; in fact, reactances can be estimated without considering that 2D geometry is not an exact representation of real 3D geometry (unlike power losses during the tests, where this fact must be taken into account).
Performance of three algorithms for frequency measurement under transient conditions
(Elsevier, 2010-05-26) Sorrentino, Elmer; Carvalho, Raul
This article compares the transient performance of three algorithms for electric frequency measurement. The algorithms are based on different techniques: (a) measurement of intervals between zero-crossings; (b) adjustment of points to a sinusoidal waveform; and (c) measurement of phase shift between fundamental components of Discrete Fourier Transform. The comparison was performed by application of the three algorithms to signals obtained by numerical simulation and to voltage waveforms sampled in experimental cases. For the case of numerically simulated signals, a theoretical frequency was defined as a reference value for the comparison with the measured values. In the experimental sampled waveforms, the effect of abrupt signal changes and the effect of filters are shown. The characteristics of the filters were selected to obtain a similar time delay in the measurement of a step in the frequency. With such filters, the three algorithms showed a similar transient behavior in all the analyzed cases. The analysis of the effect of harmonic distortion in the voltage signal is out of the scope of this article.
Nontraditional relay curves for the coordination of the ground overcurrent function with downstream fuses
(IEEE, 2014-06) Sorrentino, Elmer
This paper describes the details for the application of some nontraditional relay curves for the coordination of the ground overcurrent function with downstream fuses. These curves have a segmented shape in order to achieve the best combination of sensitivity, speed, and selectivity. For this segmented shape, greater current does not necessarily imply a shorter time. These curves can be programmed in different ways, according to the available features in the commercial relays, and the expected behavior of two options is analyzed. Both options would have satisfactory behavior although they would have different dynamic behavior.
A novel analysis of offset mho characteristic of memory-polarized and cross-polarized distance functions
(Elsevier, 2018-05-01) Sorrentino, Elmer
This article shows a novel and detailed description of the offset mho characteristic of memory-polarized and cross-polarized distance functions. The exact expressions for offset impedances are found, analyzing by symmetrical components a power system taken as an example. The power system model is general, and it includes the effect of additional interconnections between both line ends. Single line-to-ground faults, line-to-line faults, and double-line-to-ground faults are rigorously analyzed. Memory-polarized and cross-polarized distance functions have variable characteristics in the R–X plane (i.e., offset values change, depending on power system conditions), and these variations are shown for the analyzed example. Under some circumstances, the directionality of these distance functions is not evident, and the possible use of an additional directionality restraint is analyzed.
Study on the contamination rate of mineral oil in natural-ester retrofilled transformers
(IEEE, 2023-08) Montero, Andrés; García de Burgos, María Belén; Burgos Díaz, Juan Carlos; European Commission; Agencia Estatal de Investigación (España)
The replacement of mineral oil (MO) by ester (retrofilling) is a practice used in power transformers to reduce fire and environmental risk. Although measures are taken to remove traces of oil on the paper, a certain amount of MO remains, which migrates over time. This article presents a study to evaluate the migration of MO from paper to ester using techniques such as the iodine value or the measurement of permittivity and dielectric losses.
A New Method for the Quantification of the Remaining Mineral Oil in Natural-Ester Retrofilled Transformers
(IEEE, 2023-08-16) Montero Romero, Andrés; García de Burgos, María Belén; Cabanelas Valcárcel, Juan Carlos; Agencia Estatal de Investigación (España); European Commission
Assessing the amount of remaining mineral oil in retrofilled transformers is vital since that presence may worsen flash and fire point of the ester and impact the transformer dielectric performance; this article proposes a new experimental methodology to quantify the ratio of mineral oil in natural esters.
Detection of partial discharge sources using UHF sensors and blind signal separation
(MDPI, 2017-11-15) Boya Lara, Carlos Alan; Robles Muñoz, Guillermo; Parrado Hernández, Emilio; Ruiz Llata, Marta; Ministerio de Economía y Competitividad (España)
The measurement of the emitted electromagnetic energy in the UHF region of the spectrum allows the detection of partial discharges and, thus, the on-line monitoring of the condition of the insulation of electrical equipment. Unfortunately, determining the affected asset is difficult when there are several simultaneous insulation defects. This paper proposes the use of an independent component analysis (ICA) algorithm to separate the signals coming from different partial discharge (PD) sources. The performance of the algorithm has been tested using UHF signals generated by test objects. The results are validated by two automatic classification techniques: support vector machines and similarity with class mean. Both methods corroborate the suitability of the algorithm to separate the signals emitted by each PD source even when they are generated by the same type of insulation defect.
The influence of BMSs on the characterization and modeling of series and parallel Li-Ion packs
(MDPI, 2017-03) Castaño Solís, Sandra Patricia; Serrano Jiménez, Daniel; Gauchía Babé, Lucía; Sanz Feito, Javier
This work analyzes the effects of a BMS (battery management system) on the characterization and modeling of series and parallel connections of Li-ion cell packs. The Li-ion pack studied consists of four series modules connected in parallel. This pack has been characterized by means of charge, discharge and frequency tests. As a result of these tests, series and parallel influence on battery parameters have been determined. A model considering the effects of a BMS is established and compared with a model based on a single-cell approach. Experimental validations show that the single cell based approach gives poor results in comparison with a model that considers BMS effects.
Effects of fault type and pre-fault load flow on optimal coordination of directional overcurrent protections
(Elsevier B.V., 2022-08-06) Sorrentino, Elmer; Rodríguez, José Vicente
This short article shows an analysis of the effects of fault type and pre-fault load flow on the optimal coordination of directional overcurrent protections. A well-known case from the literature is taken as an example, because this case has been previously solved considering only three-phase faults and only one pre-fault load flow. The fault type and the pre-fault load flow have an influence on the results of short-circuit currents and, consequently, on the results of the optimal coordination of directional overcurrent protections. It is shown herein that the effects of pre-fault load flow and single-line-to-ground faults can be important on the results of optimal coordination. For the analyzed cases, the percentage changes in the optimal results of time delay settings can be considerably greater than the percentage changes in short-circuit currents. On the other hand, the percentage changes in optimal results of objective functions can be considerably lower than the percentage changes in short-circuit currents for the analyzed cases.
A novel method to obtain the offset mho characteristic of memory-polarized and cross-polarized distance functions of protective relays from experimental measurements
(Elsevier, 2023-03) Sorrentino, Elmer; Melián, Jorge; De Andrade, Virgilio
This article presents a novel experimental method to obtain the offset mho characteristic of memory-polarized and cross-polarized distance functions of protective relays. A proper testing method for these characteristics is not obvious because the offset impedance depends on power system conditions. In the developed method, a constant value of offset impedance is selected by the user, and the voltages and currents during the test satisfy the theoretical conditions for that offset impedance. All the points of the offset mho characteristics can be obtained using this method. The offset impedance is typically in the third quadrant for forward faults, and in the first quadrant for reverse faults. Both cases were tested, taking three relays from different manufacturers as examples. The experimental loci of the offset mho characteristic for reverse faults had not been previously obtained in the literature about this topic. Three options for performing the tests are described: with constant test current, with constant fault voltage, or with constant polarizing voltage. A discussion about some details of the relays under test is included, since those details should be known in order to perform properly the tests and/or the analysis of results. In general, the experimentally obtained loci are in concordance with the theoretical loci. The developed method does not depend on any model for the power system since it is directly oriented to the relay itself, and this fact is an excellent advantage of this method.
Investigation of the lightning impulse breakdown voltage of mineral oil based Fe3O4 nanofluids
(MDPI, 2019-12) Primo Cano, Víctor Antonio; García de Burgos, María Belén; Burgos Díaz, Juan Carlos; Pérez Rosa, Daniel; Ministerio de Economía y Competitividad (España)
The recent interest in the development of nanomaterials has led researchers to the study of their electrical properties and the applications that they may have as insulating materials. One of these applications is the use of nanofluids as electrical insulation of power transformers. It has been reported that the dielectric properties of insulating liquids in which small amounts of nanoparticles have been dispersed are, in some cases, superior to those of the base fluids. Although these materials are promising, and their application could lead to advantages for the transformer design and reliability in the future, more research is necessary to evaluate different combination of materials under a wider range of experimental conditions. In this paper, a research on the lightning impulse breakdown voltage of mineral oil and several Fe3O4-based nanofluids is presented. Fluids prepared with different concentrations of nanoparticles were subjected to impulse lightning voltages considering both positive and negative polarities. As shown in this work the positive impulse breakdown voltage of the liquids showed improvements of up to 50%; in the case of the negative impulses not significant improvements were obtained.
Online condition monitoring of MV cable feeders using Rogowski coil sensors for PD measurements
(Elsevier, 2019-02-01) Shafiq, Muhammad; Kauhaniemi, K.; Robles Muñoz, Guillermo; Isa, M.; Kumpulainen, L
Condition monitoring is a highly effective prognostic tool for incipient insulation degradation to avoid sudden failures of electrical components and to keep the power network in operation. Improved operational performance of the sensors and effective measurement techniques could enable the development of a robust monitoring system. This paper addresses two main aspects of condition monitoring: an enhanced design of an induction sensor that has the capability of measuring partial discharge (PD) signals emerging simultaneously from medium voltage cables and transformers, and an integrated monitoring system that enables the monitoring of a wider part of the cable feeder. Having described the conventional practices along with the authors' own experiences and research on non-intrusive solutions, this paper proposes an optimum design of a Rogowski coil that can measure the PD signals from medium voltage cables, its accessories, and the distribution transformers. The proposed PD monitoring scheme is implemented using the directional sensitivity capability of Rogowski coils and a suitable sensor installation scheme that leads to the development of an integrated monitoring model for the components of a MV cable feeder. Furthermore, the paper presents forethought regarding huge amount of PD data from various sensors using a simplified and practical approach. In the perspective of today's changing grid, the presented idea of integrated monitoring practices provide a concept towards automated condition monitoring.
A novel and simpler way to include transient configurations in optimal coordination of directional overcurrent protections
(Elsevier, 2020-03-01) Sorrentino, Elmer; Rodríguez, José Vicente
This article shows an original and efficient way to consider transient configurations in optimal coordination of directional overcurrent protections. In the proposed method, the constraints related to transient configurations are directly included as simple linear constraints in problem formulation. This procedure is quite different than previous approaches, which need approximate or non-linear methods to solve the optimization problem. On the other hand, it is shown here that constraints related to transient configurations can have an important effect on results. Consequently, these constraints must be included in order to properly formulate the optimization problem. Furthermore, it is shown a method to properly include the interrupting time of circuit breaker which originates the transient configuration, in order to adequately formulate the optimization problem. In the analyzed examples, the effect of including this interrupting time was very low on optimal settings, and such an effect is more notorious in the optimal value of the objective function.
Statistical study on the reference values of furanic compounds in power transformers
(IEEE, 2015-07-01) Urquiza Cuadros, Domingo Javier; García de Burgos, María Belén; Burgos Díaz, Juan Carlos; Ministerio de Economía y Competitividad (España)
This article presents a statistical study devoted to obtaining the reference values of 2FAL in power transformers.
Assessing the use of natural esters for transformer field drying
(IEEE, 2014-08-01) Villarroel Rodríguez, Rafael David; García de Burgos, María Belén; García Gómez, Diego Fernando; Burgos Díaz, Juan Carlos; Ministerio de Economía y Competitividad (España); Ministerio de Ciencia e Innovación (España)
In recent years, great attention has been paid to ester fluids as an alternative to mineral oil. Since the present use of these liquids is becoming a common practice in distribution transformers, even some experiences have been published reporting their application to power transformers. One of the main differences between ester fluid and mineral oil is the much greater capability of absorbing water by esters. In this paper, the possibility of using this kind of liquid in transformer field drying is assessed. Hot oil (HO) drying with mineral oil is one of the most widely used methods to dry transformers in the field, since it is a relatively simple and well-known process and it is less aggressive for the insulation than other drying methods. Moreover, drying the oil, while it is preferably hot, is the only method available to dry transformers online. However, the water extraction rate of the process is very poor because of the highly hydrophobic character of mineral oil and, in consequence, large drying times are needed to achieve a significant reduction in the water content of the insulation. A first theoretical analysis seems to indicate that the use of a less hydrophobic liquid would significantly reduce the drying times involved in the process. This paper aims to quantify the improvement of the HO drying process that is achieved by using ester fluids instead of mineral oil. Both drying agents were compared by means of theoretical simulations as well as laboratory tests.
Improvement of transformer liquid insulation using nanodielectric fluids: a review
(IEEE, 2018-04-24) Primo Cano, Víctor Antonio; García de Burgos, María Belén; Albarracín Sánchez, Ricardo; Ministerio de Economía y Competitividad (España)
During the last 20 years, the search for new applications for nanotechnology has become one of the busiest in science, engineering, and manufacturing. New nanotechnology-based materials with superior properties have been developed and are already used in many everyday products and processes. The application of nanotechnology to high-voltage engineering has been mainly oriented towards the development and characterization of the so-called nanodielectric materials [1]. In 1994, Lewis [2] suggested that "a major field of study in the future development of dielectrics will concern their properties when relatively few molecules are involved. Such smallness arises naturally at interfaces of nanometric thickness and will occur also when dielectrics are employed in the nano-technical devices of the future." The physical phenomena that govern the behavior of materials at sub-microscopical scale are outlined in this publication [2]. The term "nanodielectric" was introduced by Frechette [3], [4], who defined nanodielectrics as "multicomponent dielectrics possessing nanostructures, the presence of which results in the change of one or several of its dielectric properties".
A Multiphysical model to study moisture dynamics in transformers
(IEEE, 2019-08-01) García de Burgos, María Belén; Villarroel Rodríguez, Rafael David; García Gómez, Diego Fernando; Ministerio de Economía y Competitividad (España)
Moisture is one of the key variables that must be considered when determining the load profiles that can be safely applied to a transformer. The presence of high amount of water accelerates the aging rate of the transformers solid insulation, shortening the life expectancy of the equipment. Moreover, the dynamic processes of moisture migration between paper and oil must be considered in order to avoid a potential cause of failure, such as the formation of bubbles in the paper-oil interface, or the moisture saturation and the subsequent formation of liquid water in oil. These processes are linked to the changes in temperature; however, within the transformer, both processes have very different time constants, which complicates the analysis. In this paper, a mathematical model is presented, which allows us to study the moisture dynamics in a transformer. The model considers a multi-physical approach incorporating a thermal module and a moisture dynamic module that makes it possible to analyze the behavior of the moisture for a certain load profile. Some application cases are included in this paper to illustrate the model operation.
AC breakdown voltage of Fe3O4 based nanodielectric fluids. Part 2: Analysis of fluids with high moisture content
(Institute of Electrical and Electronics Engineers (IEEE), 2020-04) Primo Cano, Víctor Antonio; García de Burgos, María Belén; Burgos Díaz, Juan Carlos; Pérez Rosa, Daniel; Ministerio de Economía y Competitividad (España)
Several authors have suggested that one of the main differences between conventional insulating liquids and nanodielectric fluids is the behavior of the water in the nanodielectric fluid. It has been reported that the impact of water on the dielectric strength is reduced when nanoparticles are dispersed in the fluid, and that nanodielectric fluids present higher breakdown voltage values than the base liquids under similar moisture content. The second part of this two-part paper analyzes the effect of the presence of water on the AC breakdown voltage of several nanodielectric fluids prepared from mineral oil and Fe 3 O 4 nanoparticles in different concentrations. The fluids were conditioned to a range of moisture contents and tested under different conditions. An exhaustive measuring campaign was carried out that was completed with a non-parametric and a parametric statistical analysis of the results. As will be shown in the paper, an increase on the solubility of nanodielectric fluids has been observed which is related with the enhancement of the breakdown voltage of these liquids. The evolution of the breakdown voltage was analyzed both for fluids with similar absolute moisture contents and also for fluids with similar relative saturation conditions.
AC breakdown voltage of Fe3O4 based nanodielectric fluids. Part 1: Analysis of dry fluids
(Institute of Electrical and Electronics Engineers (IEEE), 2020-04) Primo Cano, Víctor Antonio; García de Burgos, María Belén; Burgos Díaz, Juan Carlos; Pérez Rosa, Daniel; Ministerio de Economía y Competitividad (España)
The interest in developing new nanodielectric fluids suitable for electrotechnical applications has increased significantly in the last decade. Several authors have reported experiences on fluids manufactured using different base fluids and nanoparticles. Most of these studies are focused on the comparison of the thermal and dielectric properties of the nanofluids and the base liquids and most authors have found that the addition of nanoparticles to insulating liquids can lead to an improvement of their dielectric properties. This two-part paper analyzes the enhancement of the AC breakdown voltage of several nanodielectric fluids prepared by dispersing variable concentrations of Fe 3 O 4 nanoparticles in a mineral oil. In the first part of the study, the performance of fluids that had been previously dried and degasified were tested. In the second part of the study the impact of the presence of moisture in the dielectric strength of the liquids is analyzed trying to get insight into the physical mechanisms that justify the observed enhancements when nanoparticles are added to insulating liquids.

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