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Timeline of Guillermo Robles

2019
Feb
01
Published new article




Article

Online condition monitoring of MV cable feeders using Rogowski coil sensors for PD measurements

Published: 01 February 2019 by Elsevier BV in Electric Power Systems Research

doi: 10.1016/j.epsr.2018.10.038

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.

0 Reads | 0 Citations
2019
Jan
01
Published new article




Article

Multiple Partial Discharge Source Localization in Power Cables Through Power Spectral Separation and Time-Domain Reflect...

Published: 01 January 2019 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/tim.2019.2896553

0 Reads | 0 Citations
2018
Jul
01
Published new article






Statistical correlation between partial discharge pulses magnitudes measured in the HF and UHF range

Published: 01 July 2018 by Institute of Electrical and Electronics Engineers (IEEE) in 2018 IEEE 2nd International Conference on Dielectrics (ICD)

doi: 10.1109/icd.2018.8468369

Partial discharge (PD) detection using antennas has become a useful technique for condition monitoring of high-voltage equipment. However, one of its main drawbacks is the lack of knowledge for the quantification of the PD magnitudes, which is possible when conventional capacitive dividers or high-frequency current transformers (HFCT) are used. This paper studies a possible relation between PD pulses measured in the HF and RF range. Different types of PD events were measured in the HF range using an HFCT and in the VHF/UHF range using two types of antennas. The peak value and the energy of each PD pulse have been studied for both HF and radio-frequency (RF) sensors, representing them in graphics. In addition, the possible statistical dependence between variables (peak-energy; peak-peak; energy-energy) has also been quantified.

1 Reads | 0 Citations
2018
Jul
01
Published new article






Statistical correlation between partial discharge pulses magnitudes measured in the HF and UHF range

Published: 01 July 2018 by Institute of Electrical and Electronics Engineers (IEEE) in 2018 IEEE 2nd International Conference on Dielectrics (ICD)

doi: 10.1109/icd.2018.8514603

Partial discharge (PD) detection using antennas has become a useful technique for condition monitoring of high-voltage equipment. However, one of its main drawbacks is the lack of knowledge for the quantification of the PD magnitudes, which is possible when conventional capacitive dividers or high-frequency current transformers (HFCT) are used. This paper studies a possible relation between PD pulses measured in the HF and RF range. Different types of PD events were measured in the HF range using an HFCT and in the VHF/UHF range using two types of antennas. The peak value and the energy of each PD pulse have been studied for both HF and radio-frequency (RF) sensors, representing them in graphics. In addition, the possible statistical dependence between variables (peak-energy; peak-peak; energy-energy) has also been quantified.

0 Reads | 0 Citations
2018
May
03
Published new article




Article

Radio-Frequency Localization of Multiple Partial Discharges Sources with Two Receivers

Published: 03 May 2018 by MDPI in Sensors

doi: 10.3390/s18051410

Spatial localization of emitting sources is especially interesting in different fields of application. The focus of an earthquake, the determination of cracks in solid structures, or the position of bones inside a body are some examples of the use of multilateration techniques applied to acoustic and vibratory signals. Radar, GPS and wireless sensors networks location are based on radiofrequency emissions and the techniques are the same as in the case of acoustic emissions. This paper is focused on the determination of the position of sources of partial discharges in electrical insulation for maintenance based on the condition of the electrical equipment. The use of this phenomenon is a mere example of the capabilities of the proposed method but it is very representative because the emission can be electromagnetic in the VHF and UHF ranges or acoustic. This paper presents a method to locate more than one source in space with only two receivers, one of them in a fixed position and the other describing a circumference around the first one. The signals arriving from the different sources to the antennas are first separated using a classification technique based on their spectral components. Then, the individualized time differences of arrival (TDOA) from the sources collected at different angles describe a function, angle versus TDOA, that has all the geometric information needed to locate the source. The paper will show how to derive these functions for any source analytically with the position of the source as unknown parameters. Then, it will be demonstrated that it is possible to fit the curve with experimental measurements of the TDOA to obtain the parameters of the position of each source. Finally, the technique is extended to the localization of the emitter in three dimensions.

6 Reads | 1 Citations
2018
Mar
01
Published new article




Article

Partial Discharge Spectral Characterization in HF, VHF and UHF Bands Using Particle Swarm Optimization

Published: 01 March 2018 by MDPI in Sensors

doi: 10.3390/s18030746

The measurement of partial discharge (PD) signals in the radio frequency (RF) range has gained popularity among utilities and specialized monitoring companies in recent years. Unfortunately, in most of the occasions the data are hidden by noise and coupled interferences that hinder their interpretation and renders them useless especially in acquisition systems in the ultra high frequency (UHF) band where the signals of interest are weak. This paper is focused on a method that uses a selective spectral signal characterization to feature each signal, type of partial discharge or interferences/noise, with the power contained in the most representative frequency bands. The technique can be considered as a dimensionality reduction problem where all the energy information contained in the frequency components is condensed in a reduced number of UHF or high frequency (HF) and very high frequency (VHF) bands. In general, dimensionality reduction methods make the interpretation of results a difficult task because the inherent physical nature of the signal is lost in the process. The proposed selective spectral characterization is a preprocessing tool that facilitates further main processing. The starting point is a clustering of signals that could form the core of a PD monitoring system. Therefore, the dimensionality reduction technique should discover the best frequency bands to enhance the affinity between signals in the same cluster and the differences between signals in different clusters. This is done maximizing the minimum Mahalanobis distance between clusters using particle swarm optimization (PSO). The tool is tested with three sets of experimental signals to demonstrate its capabilities in separating noise and PDs with low signal-to-noise ratio and separating different types of partial discharges measured in the UHF and HF/VHF bands.

4 Reads | 3 Citations
2018
Feb
25
Published new article




Article

Robust Condition Assessment of Electrical Equipment with One Class Support Vector Machines Based on the Measurement of P...

Published: 25 February 2018 by MDPI in Energies

doi: 10.3390/en11030486

This paper presents a system for the detection of partial discharges (PD) in industrial applications based on One Class Support Vector Machines (OCSVM). The study stresses the detection of Partial Discharges (PD) as they represent a major source of information related to degradation in the equipment. PD measurement is a widely extended technique for condition monitoring of electrical machines and power cables to avoid catastrophic failures and the consequent blackouts. One of the most important keystones in the interpretation of partial discharges is their separation from other signals considered as not-PD especially in low SNR measurements. In this sense, the OCSVM is an interesting alternative to binary SVMs since it does not need a training set with examples of all the output classes correctly labelled. On the contrary, the OCSVM learns a model of the signals acquired when the equipment is in PD-free mode, defined as a state where no degradation mechanism is active, so one only needs to make sure that the training signals were recorded under this setting. These default mode signals are easier to characterize and acquire in industrial environments than PD and lead to more robust detectors that practically do not need domain adaptation to perform in scenarios prone to different types of PD. In fact, the experimental results show that the performance of the OCSVM is comparable to that achieved by a binary SVM trained using both noise and PD pulses. Finally, the method is successfully applied to a more realistic scenario involving the detection of PD in a damaged distribution power cable.

4 Reads | 0 Citations
2017
Nov
18
Published new article




Article

Survey on the Performance of Source Localization Algorithms

Published: 18 November 2017 by MDPI in Sensors

doi: 10.3390/s17112666

The localization of emitters using an array of sensors or antennas is a prevalent issue approached in several applications. There exist different techniques for source localization, which can be classified into multilateration, received signal strength (RSS) and proximity methods. The performance of multilateration techniques relies on measured time variables: the time of flight (ToF) of the emission from the emitter to the sensor, the time differences of arrival (TDoA) of the emission between sensors and the pseudo-time of flight (pToF) of the emission to the sensors. The multilateration algorithms presented and compared in this paper can be classified as iterative and non-iterative methods. Both standard least squares (SLS) and hyperbolic least squares (HLS) are iterative and based on the Newton–Raphson technique to solve the non-linear equation system. The metaheuristic technique particle swarm optimization (PSO) used for source localisation is also studied. This optimization technique estimates the source position as the optimum of an objective function based on HLS and is also iterative in nature. Three non-iterative algorithms, namely the hyperbolic positioning algorithms (HPA), the maximum likelihood estimator (MLE) and Bancroft algorithm, are also presented. A non-iterative combined algorithm, MLE-HLS, based on MLE and HLS, is further proposed in this paper. The performance of all algorithms is analysed and compared in terms of accuracy in the localization of the position of the emitter and in terms of computational time. The analysis is also undertaken with three different sensor layouts since the positions of the sensors affect the localization; several source positions are also evaluated to make the comparison more robust. The analysis is carried out using theoretical time differences, as well as including errors due to the effect of digital sampling of the time variables. It is shown that the most balanced algorithm, yielding better results than the other algorithms in terms of accuracy and short computational time, is the combined MLE-HLS algorithm.

4 Reads | 7 Citations
2017
Nov
15
Published new article




Article

Detection of Partial Discharge Sources Using UHF Sensors and Blind Signal Separation

Published: 15 November 2017 by MDPI in Sensors

doi: 10.3390/s17112625

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.

7 Reads | 1 Citations
2017
Nov
14
Published new article






Planar localization of radio-frequency or acoustic sources with two receivers

Published: 14 November 2017 by MDPI AG in Proceedings

doi: 10.3390/ecsa-4-04892

<p>In the localization of electromagnetic or acoustic emitters, generally, when a pulse is radiated from a source, the wave will arrive to two receivers at different times. One of the advantages of measuring these time differences of arrival or TDOA is that it is not required a common clock as in other localization techniques based on the time of arrival of the pulse to the receiver. With only two sensors, all the possible points in the plane that would give the same TDOA describe a hyperbola. Using an independent third receiver and calculating the intersection of the three hyperbolas will give the position of the source. Therefore, planar localization of emitters using multilateration techniques can be solved at least with three receivers. This paper presents a method to locate sources in a plane with only two receivers reducing the number of acquisition channels and hence, the cost of the equipment. One of the receivers is in a fixed position and the other describes a circumference around the first one. The TDOA are measured at different angles completing a total turn and obtaining a periodic function, angle versus TDOA, that has all the geometric information needed to locate the source. The paper will show how to derive this function analytically with the distance from the fixed receiver to the source and a bearing angle as parameters. Then, it will be demonstrated that it is possible to fit the curve with experimental measurements to obtain the parameters of the position of the source.</p>

22 Reads | 1 Citations
2017
Feb
01
Published new article




Article

Partial discharges and noise separation using spectral power ratios and genetic algorithms

Published: 01 February 2017 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/TDEI.2016.005898

Accurate measurements of partial discharge (PD) activity is essential for the application of this technique to condition-based monitoring. Noise and PD source characterization is necessary to fulfil that goal, since the interpretation of classical phase-resolved partial discharge (PRPD) patterns is usually complex for the measurements done in field. A successful pulse source separation prior to the identification seems to be the best option. The authors proposed in a previous work a method based on spectral power ratios (PR) to separate pulse sources with quite good experimental results. This technique calculates the spectral power in two frequency bands to obtain two parameters which, represented in a 2-dimensional map (PR map), characterize each pulse source by a cluster of points. The main difficulty of this technique is the choice of the appropriate frequency intervals that give a good separation of clusters, which sometimes can be cumbersome by manual means. Thus, this paper presents an unsupervised technique to select the two frequency intervals that gives the best separation among several clusters. This will give a great support for the system user to separate PD and noise sources in real measurements. The authors used genetic algorithms (GAs) to select these frequencies, with good results in several real experiments.

0 Reads | 3 Citations
2016
Nov
14
Published new article






High frequency inductive energy harverster for the maintenance of electric assets

Published: 14 November 2016 by MDPI AG in Proceedings

doi: 10.3390/ecsa-3-S6001

<p>Extracting tiny amounts of energy from non-conventional sources using Peltier cells, piezoelectrics, antennas or inductive probes has become very popular in recent years to power low-consuming sensors in IoT applications and smart grids. These energy harvesting methods rely on the continuous generation of small quantities of electrical energy scavenged from heat, vibration or electromagnetic emissions. This energy is stored in batteries or capacitors reaching low-voltage levels that cannot be used directly to power any device. In general, the voltage is boosted to more appropriate levels with a converter. Using inductive sensors to harvest energy from electrical power lines is common knowledge. Obtaining this energy from high-power low-frequency signals is currently possible and, in some cases, reliable and profitable. The aim of this paper is to evaluate the possibility of harvesting energy from extremely low-power and high-frequency events that occur in electrical assets when the insulation is damaged. These events, called partial discharges, are used in electrical maintenance to detect possible defects in the insulation. Evaluating partial discharge activity is a common protocol in all utilities that requires the use of expensive sensors and acquisition systems, and in most occasions, decommissioning the asset to connect the measuring system. The energy from these phenomena is stored in capacitors and the use of a high-frequency voltage multiplier allows to reach voltages close to 1 V. This voltage is proportional to the number of partial discharges in a certain time span. Therefore, if the number of partial discharges per time-unit has increased noticeably, the insulation has deteriorated and the asset should be decommissioned to evaluate the damages. The paper tests the possibility of using this method as an early-warning system in the maintenance of electrical assets.</p> <p></p> <p></p> <p></p>

11 Reads | 0 Citations
2016
Nov
14
Published new article






<span>The influence of antenna positioning errors on the radio-frequency localization of partial discharges sources</spa...

Published: 14 November 2016 by MDPI AG in Proceedings

doi: 10.3390/ecsa-3-E003

<p>Electrical insulation can have imperfections due to manufacturing or ageing. When the insulation is electrically stressed, discharges may happen in these inhomogeneous imperfect locations resulting in partial discharge (PD) which have very fast rise times and short time durations. Since charges are accelerated within PD activity, radiated electromagnetic energy across a wide bandwidth of frequencies can occur. The measurement of the radiated PD energy is widely employed to identify defective insulation within high voltage equipment. Based on assessment of the strength and nature of the emitted PD signals, determination is made to carry out predictive maintenance in order to prevent equipment breakdown. The location of emitted radiated PD signals may be determined using multi-lateration techniques using an array of at least 4 antennas. Depending on the relative position between the antennas and the PD source, the radiated emissions from the PD source arrive at each antenna at different times. The relative time differences of arrivals (TDOA) together with the antennas position are variables used to locate the PD source in 3D space. The effect on the location error of a PD source using TDOA calculations based on acquisition sample time errors is a topic which has previously been studied (see bibliography). This paper now investigates the accuracy on PD location as a consequence of error on the measured positions of the antennas. This paper evaluates the influence of positional antenna error on the possible accuracy of the localization of the PD source. This error is analyzed for 3 different antenna array layouts and for different vector directions from the arrays. Additionally, the least sensitive layout with regard to positioning errors is proposed to assist in improving the location accuracy of PD sources.</p>

6 Reads | 0 Citations
2016
Oct
13
Published new article




Article

Study on the self-integration of a Rogowski coil used in the measurement of partial discharges pulses

Published: 13 October 2016 by Springer Nature in Electrical Engineering

doi: 10.1007/s00202-016-0456-4

0 Reads | 1 Citations
2016
Sep
16
Published new article






Antennas in Partial Discharge Sensing System

Published: 16 September 2016 by Springer Nature in Handbook of Antenna Technologies

doi: 10.1007/978-981-4560-44-3_95

0 Reads | 0 Citations
2016
Aug
01
Published new article




Article

Multiple partial discharge source discrimination with multiclass support vector machines

Published: 01 August 2016 by Elsevier BV in Expert Systems with Applications

doi: 10.1016/j.eswa.2016.02.014

1 Reads | 8 Citations
2016
Jul
01
Published new article






Ageing study on enameled magnet wires through statistical analysis of conventional partial discharge magnitudes and repe...

Published: 01 July 2016 by Institute of Electrical and Electronics Engineers (IEEE) in 2016 IEEE International Conference on Dielectrics (ICD)

doi: 10.1109/icd.2016.7547699

As a result of the use of inverted-fed drives, enameled magnet wires of induction motors are suffering from partial discharge (PD) activity. This is a clear ageing mechanism for the machines which leads to unexpected failures in these systems. Ageing characterization of this insulation system is essential for these applications. In this paper, several statistical PD quantities which account for PD magnitude and repetition rate are studied in ageing processes of twisted pairs of enameled magnet wires. The resulting ageing curves have been adjusted to several mathematical functions in order to check if any clear tendency is detected.

0 Reads | 0 Citations
2016
Jul
01
Published new article






Statistical analysis of RF signals emitted by partial discharges

Published: 01 July 2016 by Institute of Electrical and Electronics Engineers (IEEE) in 2016 IEEE International Conference on Dielectrics (ICD)

doi: 10.1109/icd.2016.7547660

Electromagnetic radiation emissions from partial discharges (PD) can be measured, which could be helpful for avoiding unwanted asset disconnections in the power grid for insulation evaluation. These radio-frequency (RF) measurements do not require galvanic contact with high-voltage (HV) devices, which seems to be a clear advantage, but the lack of synchronization voltage makes PD source recognition a difficult task. Moreover, the presence of RF noise sources in the wideband required for PD detection, can lead to false warnings in the HV apparatus evaluation. In this paper, some specific parameters for signal characterization have been used to study noise and PD emissions. A digital acquisition system has been programmed to measure thousands of emissions from environmental noise and controlled PD sources in laboratory experiments to analyze the dispersive character of the recorded spectra.

0 Reads | 0 Citations
2016
Jul
01
Published new article






Ensemble Empirical Mode Decomposition for the denoising of partial discharges measured in UHF

Published: 01 July 2016 by Institute of Electrical and Electronics Engineers (IEEE) in 2016 IEEE International Conference on Dielectrics (ICD)

doi: 10.1109/icd.2016.7547777

Monitoring dielectric insulation systems is important for the maintenance of electric assets. In open-air substations, this task can be done with antennas because they cover wide areas and detect the electromagnetic emissions of one of the most common deterioration processes: partial discharges (PD). This detection can be affected by radio-frequency interferences that contaminate the measurements and may lead to errors in the diagnosis. Thus, it is necessary to apply denoising techniques to recover the pulsed signal of this PD activity. The aim of this paper is to propose an adaptive and automatic algorithm named Ensemble Empirical Mode Decomposition(EEMD) which consists in the decomposition of the signal in several Intrinsic Mode Functions (IMF) that will be used to reject UHF interferences superimposed to PD pulses.

0 Reads | 0 Citations
2016
Apr
15
Published new article




Article

Antenna Deployment for the Localization of Partial Discharges in Open-Air Substations

Published: 15 April 2016 by MDPI in Sensors

doi: 10.3390/s16040541

Partial discharges are ionization processes inside or on the surface of dielectrics that can unveil insulation problems in electrical equipment. The charge accumulated is released under certain environmental and voltage conditions attacking the insulation both physically and chemically. The final consequence of a continuous occurrence of these events is the breakdown of the dielectric. The electron avalanche provokes a derivative of the electric field with respect to time, creating an electromagnetic impulse that can be detected with antennas. The localization of the source helps in the identification of the piece of equipment that has to be decommissioned. This can be done by deploying antennas and calculating the time difference of arrival (TDOA) of the electromagnetic pulses. However, small errors in this parameter can lead to great displacements of the calculated position of the source. Usually, four antennas are used to find the source but the array geometry has to be correctly deployed to have minimal errors in the localization. This paper demonstrates, by an analysis based on simulation and also experimentally, that the most common layouts are not always the best options and proposes a simple antenna layout to reduce the systematic error in the TDOA calculation due to the positions of the antennas in the array.

5 Reads | 6 Citations
2015
Nov
10
Published new article






Antenna array layout for the localization of partial discharges in open-air substations

Published: 10 November 2015 by MDPI AG in Proceedings of 2nd International Electronic Conference on Sensors and Applications

doi: 10.3390/ecsa-2-E008

<p>Partial discharges are ionization processes inside or on the surface of dielectrics that can unveil insulation problems in electrical equipment. The charge accumulated in the dielectric is released under certain environmental and voltage conditions attacking the insulation both physically and chemically. The final consequence of a continuous occurrence of these events is the breakdown of the dielectric. The electron avalanche provokes a derivative of the electric field close to the damaged insulation creating an electromagnetic impulse that can be detected with antennas. The localization of the source of partial discharges helps in the identification of the piece of equipment that has to be decommissioned. This can be done deploying antennas in open-air substations and calculating the time difference of arrival (TDOA) of the electromagnetic pulses. This parameter is critical in the localization and small errors can lead to a great displacement of the calculated position of the source. Usually, four antennas are used to find the source in space but the array has to be correctly deployed to have minimal errors in the localization. This paper demonstrates theoretically and experimentally that the most common layouts are not the best option and proposes a simple antenna layout to reduce the systematic error in the TDOA calculation due to the positions of the antennas.</p>

7 Reads | 1 Citations
2015
Sep
01
Published new article




Article

Separation of sources in radiofrequency measurements of partial discharges using time–power ratio maps

Published: 01 September 2015 by Elsevier BV in ISA Transactions

doi: 10.1016/j.isatra.2015.04.006

Partial discharges measurement is one of the most useful tools for condition monitoring of high-voltage (HV) equipment. These phenomena can be measured on-line in radiofrequency (RF) with sensors such as the Vivaldi antenna, used in this paper, which improves the signal-to-noise ratio by rejecting FM and low-frequency TV bands. Additionally, the power ratios (PR), a signal-processing technique based on the power distribution of the incoming signals in frequency bands, are used to characterize different sources of PD and electromagnetic noise (EMN). The calculation of the time length of the pulses is introduced to separate signals where the PR alone do not give a conclusive solution. Thus, if several EM sources could be previously calibrated, it is possible to detect pulses corresponding to PD activity.

0 Reads | 12 Citations
2015
Aug
22
Published new article






Antennas in Partial Discharge Sensing System

Published: 22 August 2015 by Springer Nature in Handbook of Antenna Technologies

doi: 10.1007/978-981-4560-75-7_95-1

0 Reads | 1 Citations
2015
Aug
01
Published new article




Article

Location of partial discharges sources by means of blind source separation of UHF signals

Published: 01 August 2015 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/tdei.2015.004482

Partial discharges (PD) detection is a widely extended technique for the diagnosis of electrical equipment. Ultra-high frequency (UHF) detection techniques appear as the best choice if the goal is to detect PD online and to locate devices with insulation problems in substations and overhead lines. The location of PD is based on the determination of the difference of the time of arrival of electromagnetic pulses radiated by a source of PD to an array of antennas distributed around the monitored area. However, when measuring electromagnetic pulses radiated by PD activity many interfering signals, such as those coming from television (TV), global positioning system (GPS), wireless communication signals and others coming from electrical equipment distort the waveform detected by the sensors. Under these circumstances, the application of traditional techniques to estimate the time differences may fail. In this paper, the use Blind Source Separation (BSS) techniques applied to pairs of UHF sensors is proposed to extract the information of the difference of the time of arrival of the electromagnetic pulses radiated by a source of PD. The paper is focused on the application of the algorithm and the description of an experimental setup for controlled generation and detection of PD to verify the performance of the proposed technique. Author(s) Boya, C. Universidad Carlos III de Madrid, 1Department of Electronic Technology, Spain Rojas-Moreno, M.V. ; Ruiz-Llata, M. ; Robles, G.

0 Reads | 4 Citations
2015
Aug
01
Published new article




Article

Automatic selection of frequency bands for the power ratios separation technique in partial discharge measurements: part...

Published: 01 August 2015 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/tdei.2015.004822

Partial discharge (PD) measurement is a widely extended technique for the diagnosis of electrical machines and power cables. Since PD and noise recognition is really important in industrial environments, the authors proposed the use of the spectral Power Ratios (PR) of the detected high-frequency (HF) signals, which show promising results. However, the frequency bands selected for their calculation have a clear influence on the position of the clusters in the classification maps. Following this research trend, a new algorithm for the automatic selection of the frequency bands which gives a proper separation between the clusters, has been proposed in part I of this paper. The first results presented in this paper revealed a good behavior of the technique for PD and noise separation in simple test objects. In this second part of the paper, more results from the application of this system to PD source recognition in simple test objects and also in real equipment are developed. Author(s) Ardila-Rey, J.A. Universidad T??cnica Federico Santa Mar??a, Chile Martinez-Tarifa, J.M. ; Robles, G.

0 Reads | 1 Citations
2015
Aug
01
Published new article




Article

Automatic selection of frequency bands for the power ratios separation technique in partial discharge measurements: part...

Published: 01 August 2015 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/tdei.2015.004821

Partial discharge (PD) measurements are important for the monitoring of the status of almost any type of high-voltage equipment. The use of this technique for on-line measurements involves several challenges related to noise rejection and PD source recognition. In order to face these issues, pulse shape analyses are made in high-frequency and very-high-frequency ranges. The authors proposed in a previous paper the so-called Power Ratios (PR) of the spectra as useful parameters for pulse source separation in a two-dimensional approach. This technique provides good results, but its reliability depends on the appropriate selection of two frequency intervals where these spectral power ratios are calculated. In order to improve this separation system, the authors propose an algorithm that provides the frequency intervals necessary to obtain very good separation results in several experimental setups. The explanation of the system and the results obtained are presented in two papers. The simultaneous measurements of pulse sources (PD or noise) are complemented with pulse characterization when only one single source is active in order to check that the selected frequency intervals are appropriate. In this first paper, the authors summarize the fundamentals of the proposed algorithm and its first results for PD and noise separation in simple test objects that create corona, internal and surface discharges. Author(s) Martinez-Tarifa, J.M. Universidad Carlos III de Madrid Legan??s Departamento de Ingenier??a El??ctrica, Spain Ardila-Rey, J.A. ; Robles, G.

0 Reads | 1 Citations
2015
May
01
Published new article






On the use of spectral power ratios for partial discharge and noise separation in radiofrequency measurements

Published: 01 May 2015 by Institute of Electrical and Electronics Engineers (IEEE) in 2015 IEEE International Instrumentation and Measurement Technology Conference (I2MTC)

doi: 10.1109/i2mtc.2015.7151556

Partial discharge (PD) measurements are commonly used in the maintenance of high-voltage equipment. New research is being done devoted to the measurement of the phenomenon in radiofrequency (RF) because it has several advantages compared to other classical methods. However, noise rejection is still one of the main challenges to face. In this paper, a method based on the power spectral share in bands of frequency, already used in classical measurements, is applied to separate RF signals emitted by PD and noise. Author(s) Ardila-Rey, J.A. Dept. de Ing. Electr., Univ. Tec. Federico Santa Maria, Santiago de Chile, Chile Albarracin, R. ; Martinez-Tarifa, J.M. ; Robles, G.

0 Reads | 0 Citations
2015
Apr
27
Published new article




Article

Separation of Radio-Frequency Sources and Localization of Partial Discharges in Noisy Environments

Published: 27 April 2015 by MDPI in Sensors

doi: 10.3390/s150509882

The detection of partial discharges (PD) can help in early-warning detection systems to protect critical assets in power systems. The radio-frequency emission of these events can be measured with antennas even when the equipment is in service which reduces dramatically the maintenance costs and favours the implementation of condition-based monitoring systems. The drawback of these type of measurements is the difficulty of having a reference signal to study the events in a classical phase-resolved partial discharge pattern (PRPD). Therefore, in open-air substations and overhead lines where interferences from radio and TV broadcasting and mobile communications are important sources of noise and other pulsed interferences from rectifiers or inverters can be present, it is difficult to identify whether there is partial discharges activity or not. This paper proposes a robust method to separate the events captured with the antennas, identify which of them are partial discharges and localize the piece of equipment that is having problems. The separation is done with power ratio (PR) maps based on the spectral characteristics of the signal and the identification of the type of event is done localizing the source with an array of four antennas. Several classical methods to calculate the time differences of arrival (TDOA) of the emission to the antennas have been tested, and the localization is done using particle swarm optimization (PSO) to minimize a distance function.

4 Reads | 16 Citations
2015
Feb
04
Published new article




Article

Development of a Moisture-in-Solid-Insulation Sensor for Power Transformers

Published: 04 February 2015 by MDPI in Sensors

doi: 10.3390/s150203610

Moisture is an important variable that must be kept under control to guarantee a safe operation of power transformers. Because of the hydrophilic character of cellulose, water mainly remains in the solid insulation, while just a few parts per million are dissolved in oil. The distribution of moisture between paper and oil is not static, but varies depending on the insulation temperature, and thus, water migration processes take place continuously during transformers operation. In this work, a sensor is presented that allows the determination of the moisture content of the transformer solid insulation in the steady state and during the moisture migration processes. The main objective of the design is that the electrodes of the sensor should not obstruct the movement of water from the solid insulation to the oil, so the proposed prototype uses a metallic-mesh electrode to do the measurements. The measurement setup is based on the characterization of the insulation dielectric response by means of the frequency dielectric spectroscopy (FDS) method. The sensitivity of the proposed sensor has been tested on samples with a moisture content within 1% to 5%, demonstrating the good sensitivity and repeatability of the measurements.

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2014
Feb
19
Published new article




Article

Inductive Sensor Performance in Partial Discharges and Noise Separation by Means of Spectral Power Ratios

Published: 19 February 2014 by MDPI in Sensors

doi: 10.3390/s140203408

Partial discharge (PD) detection is a standardized technique to qualify electrical insulation in machines and power cables. Several techniques that analyze the waveform of the pulses have been proposed to discriminate noise from PD activity. Among them, spectral power ratio representation shows great flexibility in the separation of the sources of PD. Mapping spectral power ratios in two-dimensional plots leads to clusters of points which group pulses with similar characteristics. The position in the map depends on the nature of the partial discharge, the setup and the frequency response of the sensors. If these clusters are clearly separated, the subsequent task of identifying the source of the discharge is straightforward so the distance between clusters can be a figure of merit to suggest the best option for PD recognition. In this paper, two inductive sensors with different frequency responses to pulsed signals, a high frequency current transformer and an inductive loop sensor, are analyzed to test their performance in detecting and separating the sources of partial discharges.

0 Reads | 10 Citations
2013
Nov
01
Published new article




Article

Partial discharge source recognition by means of clustering of spectral power ratios

Published: 01 November 2013 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/0957-0233/24/12/125605

0 Reads | 1 Citations
2013
Aug
01
Published new article




Article

Partial discharge and noise separation by means of spectral-power clustering techniques

Published: 01 August 2013 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/TDEI.2013.6571466

Partial Discharges (PDs) are one of the most important classes of ageing processes that occur within electrical insulation. The measurement of PDs is useful in the diagnosis of electrical equipment because PDs activity is related to different ageing mechanisms. Classical Phase-Resolved Partial Discharge (PRPD) patterns are able to identify PD sources when they are related to a clear degradation process and when the noise level is low compared to the amplitudes of the PDs. However, real insulation systems usually exhibit several PD sources and the noise level is high, especially if measurements are performed on-line. High-frequency (HF) sensors and advanced signal processing techniques have been successfully applied to identify these phenomena in real insulation systems. In this paper, spectral power analyses of PD pulses and the spectral power ratios at different frequencies were calculated to classify PD sources and noise by means of a graphical representation in a plane. This technique is a flexible tool for noise identification and will be useful for pulse characterization.

0 Reads | 10 Citations
2013
Jun
01
Published new article






On the use of Vivaldi antennas in the detection of partial discharges

Published: 01 June 2013 by Institute of Electrical and Electronics Engineers (IEEE) in 2013 IEEE International Conference on Solid Dielectrics (ICSD)

doi: 10.1109/icsd.2013.6619887

Due to their impulsive nature, partial discharges in insulation systems emit in a broad band of frequencies ranging from tens of megahertz to gigahertz. Antennas can be placed at secure distances from the high-voltage source and measure partial discharges pulses on-line. The energy of partial discharges coexists with strong electromagnetic emissions such as frequency modulated radio, television broadcasting and mobile telephones. Then, the antennas should be tuned to detect the emission from partial discharges in bands where the electromagnetic noise is not so important. They should also be capable of receiving in a broad range of frequencies so resonant antennas should be avoided. Vivaldi antennas can be designed to detect emissions from a desired tuned frequency and extended to a band as wide as necessary. This makes them a valuable tool to detect partial discharges avoiding electromagnetic noise present at lower frequencies.

0 Reads | 1 Citations
2013
Jun
01
Published new article






Moisture sensor to characterize transformer solid insulations in transformers under non-equilibrium conditions

Published: 01 June 2013 by Institute of Electrical and Electronics Engineers (IEEE) in 2013 IEEE International Conference on Solid Dielectrics (ICSD)

doi: 10.1109/icsd.2013.6619888

Moisture is an important variable that must be kept under control to guarantee a safe operation of power transformers. Because of the hydrophilic character of cellulose, water mainly remains in the solid insulation while just a few parts per million are dissolved in oil. The distribution of moisture between paper and oil is not static but varies depending on the insulation temperature and thus, water migration processes take place continuously during transformers operation [1]. In this work, a sensor is presented to determine the moisture content in the solid insulation of transformers during moisture migration processes. The main objective of the design is that the electrodes of the sensor should not obstruct the movement of water from the solid insulation to the oil, so the proposed prototype uses a metallic mesh-electrode. The measurement scheme is based on the characterization of the insulation dielectric response by means of the Frequency Dielectric Spectroscopy (FDS) method.

0 Reads | 0 Citations
2013
Jun
01
Published new article






Chromatic classification of RF signals for partial discharges and noise characterization

Published: 01 June 2013 by Institute of Electrical and Electronics Engineers (IEEE) in 2013 IEEE International Conference on Solid Dielectrics (ICSD)

doi: 10.1109/icsd.2013.6619863

Electromagnetic radiation emissions from partial discharges (PD) can be measured, which could be helpful for avoiding unwanted asset disconnections in the power grid for insulation evaluation. These radio-frequency (RF) measurements do not require galvanic contact with high-voltage (HV) devices, which seems to be a clear advantage, but the lack of synchronization voltage makes PD source recognition a difficult task. Moreover, the presence of RF noise sources in the wideband required for PD detection, can lead to false warnings in the HV apparatus evaluation. In this paper, some specific parameters for signal characterization have been used in three-dimensional maps: signal energy, bandwidth and characteristic frequency. A digital acquisition system has been programmed to measure thousands of emissions from environmental noise and controlled PD sources in laboratory experiments. The aim of this paper is to state if this signal classification technique is reliable for PD and noise characterization in the RF range.

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2013
May
01
Published new article




Article

Antenna Parametrization for the Detection of Partial Discharges

Published: 01 May 2013 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/TIM.2012.2223332

Partial discharge (PD) detection is a widely extended technique for electrical insulation diagnosis. Ultrahigh-frequency detection techniques appear as a feasible alternative to traditional methods owing to their inherent advantages such as the capability to detect PDs online and to locate the piece of equipment with insulation problems in substations and cables. In this paper, four antennas are thoroughly studied by means of their theoretical and experimental behavior when measuring electromagnetic pulses radiated by PD activity. The theoretic study of the band of frequencies in which the pulse emits and the measurement of the parameters S11 are complemented with the frequency response and wavelet transform of a set of 500 time signals acquired by the antennas, and the results are analyzed in detail.

0 Reads | 17 Citations
2013
Apr
01
Published new article




Article

Shielding effect of power transformers tanks in the ultra-high-frequency detection of partial discharges

Published: 01 April 2013 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/TDEI.2013.6508772

Partial discharges (PD) measurement is a well-known technique for judgment of the condition of power transformer offline. Phase-resolved PD measurement is a normalized technique for PD tests, but noise, especially by PD-measurements onsite is sometimes difficult to reject, and a post-processing of a pattern is necessary to separate different sources. Higher-frequency-detection devices and processing strategies are useful for PD classification and identification. Recently, ultra-high-frequency (UHF) detection by means of antennas has been shown to be a promising detection system for both offline and online PD-measurements. However, it is necessary to assess whether PD source separation and classification is possible by means of pulse analysis because some additional UHF noise sources are coupled to the detected signals, and it is not clear whether different sources produce different pulses. In this study, the attenuation effect of the metallic tank of a power transformer on the inner PD activity when measured outside the tank was studied. Additionally, experiments were conducted to detect and characterize two different PD sources (internal and external discharges) using two antennas measuring the same phenomenon inside and outside of a transformer. It will also be shown that broadband UHF signals are useful for PD recognition and that a deep study of frequencies below 500 MHz can separate PD occurring inside from those occurring outside when measured with an antenna outside the tank.

0 Reads | 5 Citations
2012
Oct
01
Published new article




Article

Electro-acoustic detection, identification and location of partial discharge sources in oil-paper insulation systems

Published: 01 October 2012 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/TDEI.2012.6311502

The detection of Partial Discharges (PD) is a reliable technique to analyze the status of electrical insulation in power transformers. Phase resolved partial discharge patterns are being complemented with high frequency pulse waveform analysis, in order to identify discharge sources. In addition to this, acoustic techniques are being implemented trying to locate PD sites in large power transformers. In this work, an inductive loop sensor will be used to identify two different PD sources by means of the energy distribution of the detected waveforms. Additionally, these PD sources will be located by means of acoustic measurements with an electrical reference, through the analysis of the acoustic activity detected for each sensor individually.

0 Reads | 7 Citations
2012
May
01
Published new article






Partial discharges and noise separation in high frequency signals using inductive sensors

Published: 01 May 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 IEEE International Instrumentation and Measurement Technology Conference Proceedings

doi: 10.1109/i2mtc.2012.6229136

Partial discharges in high voltage equipment are a cause and consequence of premature ageing. Thus, its accurate measurement is an important diagnosis tool trying to avoid premature failures. Classical phase resolved patterns are now completed with pulse waveform analysis in order to discriminate between PD sources and PD from noise. For this purpose, high frequency inductive sensors are being used in recent years. In this paper, a fixed post-processing technique for PD pulse waveforms will be used to discriminate between discharges from electrical noise for two inductive sensors: a commercial High Frequency Current Transformer and a newly developed inductive loop sensor. Results will prove that this novel inductive loop sensor is able to discriminate PD from electrical noise for several test objects.

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2012
May
01
Published new article






A Partial Discharges acquisition and statistical analysis software

Published: 01 May 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC)

doi: 10.1109/i2mtc.2012.6229187

Partial Discharges (PDs) are responsible for unexpected failures in power system equipment, so their measurement is a fundamental tool for electrical equipment maintenance. In order to characterize PDs activity, some statistical magnitudes are necessary. For this purpose, PDs acquisition and processing is an important tool for critical decisions related to power systems. In this paper, the main difficulties and challenges facing PDs detection, acquisition and processing are presented. Results will be compared to a commercial PDs detection system.

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2012
May
01
Published new article






Antenna selection and frequency response study for UHF detection of partial discharges

Published: 01 May 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC)

doi: 10.1109/i2mtc.2012.6229440

Partial Discharge (PD) detection is a widely extended technique for electrical insulation diagnosis. Classical PD detection by means of phase resolved patterns require electrical connections to the power equipment and is sensitive to many noise sources. Ultra High Frequency (UHF) detection techniques are being recently proposed to overcome these problems, and to detect partial discharges on-line. In this paper, four antennas will be tested in order to compare their response to this physical phenomenon.

0 Reads | 1 Citations
2011
Aug
01
Published new article




Article

Self-integrating inductive loop for measuring high frequency pulses

Published: 01 August 2011 by AIP Publishing in Review of Scientific Instruments

doi: 10.1063/1.3622521

High frequency pulses can be measured by means of inductive sensors. The main advantage of these sensors consists of non-contact measurements that isolate and protect measuring equipment. The objective of this paper is to present the implementation of an inductive sensor for measuring rapidly varying currents. It consists of a rectangular loop with a resistor at its terminals. The inductive loop gives the derivative of the current according to Faraday's law and the resistor connected to the loop modifies the sensor's frequency response to obtain an output proportional to the current pulse. The self-integrating inductive sensor was validated with two sensors, a non-inductive resistor and a commercial high frequency current transformer. The results were compared to determine the advantages and drawbacks of the probe as an adequate inductive transducer.

0 Reads | 1 Citations
2011
May
01
Published new article




Article

Study of an Inductive Sensor for Measuring High Frequency Current Pulses

Published: 01 May 2011 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/TIM.2010.2090056

The objective of this paper is to present a simple sensor based on Faraday's Law together with an integration and amplifying stage and used this for measuring fast current pulses. Its behavior in time and frequency is tested by measuring Partial Discharges (PD) in electric insulation systems following the guidelines given in the standard IEC 60270. The measurements are also taken with two other sensors, a commercial high frequency current transformer and a resistive transducer, with the aim of comparing the results obtained with the proposed probe and obtaining an estimation of its sensitivity. An estimation of the uncertainty of the measurements is also calculated obtaining an error similar to other commercial devices.

0 Reads | 3 Citations
2011
Feb
01
Published new article




Article

Critical Parameters for Mutual Inductance Between Rogowski Coil and Primary Conductor

Published: 01 February 2011 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/TIM.2010.2051591

We present the results of an analytical study aimed at characterizing the critical parameters affecting the mutual inductance M between Rogowski coils and primary conductors. The analysis is based on the method of the mutual partial inductances and it is applied to various case studies. Calculations are carried out for Rogowski coils having a few turns, hundreds, and even thousands of turns with uniform and nonuniform windings. We also provide the results of an experimental analysis performed on a Rogowski coil with a small number of turns for comparison with the proposed technique.

0 Reads | 4 Citations
2010
Dec
01
Published new article




Article

Influence of leakage magnetic fields on partial discharge activity in power transformers

Published: 01 December 2010 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Dielectrics and Electrical Insulation

doi: 10.1109/TDEI.2010.5658222

Partial discharges are a clear ageing agent on insulating materials used in high voltage electrical machines. For this reason, there is increasing interest in measuring this phenomenon in an effort to forecast unexpected failures in electrical equipment. Despite the fact that normalized tests have been carried out for years, the effect of leakage magnetic fluxes in transformers and rotating machines stator windings has not yet been considered. The authors show that common stray fluxes in typical high voltage machines modify partial discharge activity, so the interaction between ionization processes and magnetic fields is analysed. This might have a clear effect on the results extracted from on-line and off-line partial discharge measurements.

0 Reads | 0 Citations
2010
Sep
08
Published new article




Article

Partial discharge pulse shape recognition using an inductive loop sensor

Published: 08 September 2010 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/0957-0233/21/10/105706

0 Reads | 2 Citations
2010
May
01
Published new article






An inductive transducer for the measurement of high frequency pulses with applicability in the detection of partial disc...

Published: 01 May 2010 by Institute of Electrical and Electronics Engineers (IEEE) in 2010 IEEE Instrumentation & Measurement Technology Conference Proceedings

doi: 10.1109/imtc.2010.5487995

Measuring fast current pulses requires devices with ample broad bands. The approach of this paper is to present a simple sensor based on the Faraday's Law together with an integrating and amplifying stage. Its validation is done by means of the detection of Partial Discharges (PD) in electric insulation systems following the guidelines given in the standard IEC 60270. These measurements are also taken with a high frequency current transformer with the aim of comparing the results obtained with the proposed probe.

0 Reads | 0 Citations
2009
Nov
01
Published new article




Article

Inductive Sensor for Measuring High Frequency Partial Discharges Within Electrical Insulation

Published: 01 November 2009 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/TIM.2009.2021239

Partial discharges are not only a consequence but a symptom of insulation degradation in electrical equipment. Partial discharges are revealed outside the insulation as very narrow high-frequency pulses that were superimposed to the grid frequency high-level voltages or currents and thus are fairly hard to detect. This paper presents an application of a new inductively coupled sensor that allows these signals to be measured in an accurate inexpensive manner. The sensor model and its frequency and geometry-dependent behavior are studied to increase the probe sensitivity as much as possible. Its measuring capability in real insulation systems that were subjected to high partial discharge activity will be tested.

0 Reads | 4 Citations
2009
May
01
Published new article






Critical parameters for mutual inductance between Rogowski coil and primary conductor

Published: 01 May 2009 by Institute of Electrical and Electronics Engineers (IEEE) in 2009 IEEE Intrumentation and Measurement Technology Conference

doi: 10.1109/imtc.2009.5168487

We present the results of an analytical study aimed at characterizing the mutual inductance M of Rogowski coils for generic paths of the primary wire and for nonuniform windings. In order to obtain such data, we performed a series of calculations based on the method of the mutual partial inductances and on the application of the Biot-Savart-Laplace law. Finally, we discuss the role of some critical parameters affecting M.

0 Reads | 0 Citations
2009
Feb
01
Published new article




Article

Measurement of Asymmetric Minor Loops in Soft Ferrites Up to Medium Frequencies

Published: 01 February 2009 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Instrumentation and Measurement

doi: 10.1109/TIM.2008.928403

An accurate measurement of the hysteresis cycle of magnetic cores is a crucial step in its characterization due to the importance that its nonlinear and past-dependent effects can have on the correct operation in most electric and electronic circuits. The measurements of asymmetric minor loops, in conditions where Foucault currents can be neglected, can be useful to train models. Performing such measurements only at very low frequencies is not a solution, given the need to identify dynamic parameters of the aforementioned models. In a previous paper, the authors proposed a method for measuring major loops of hysteresis cycles up to medium frequencies, given the limitation of the classic method when increasing frequency. The method, which has been improved in this paper, is tested by measuring nonsymmetric loops of the hysteresis cycle at medium frequencies. Simulated and experimental results are provided.

0 Reads | 0 Citations
2019
Mar
20
Affiliation update




Guillermo Robles added a new affiliation: Universidad Carlos III de Madrid

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