Open access: http://www.mdpi.com/2504-3900/1/2/5/
G. Robles and J. Molina, High frequency inductive energy harvester for the maintenance of electrical assets, In Proceedings of the 3rd Int. Electron. Conf. Sens. Appl, 15–30 November 2016; Sciforum Electronic Conference Series, Vol. 3, 2016 , S6001; doi:10.3390/ecsa-3-S6001
Abstract—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.
Keywords—Energy harvesting, maintenance, inductive sensors, high frequency pulses, partial discharges.
J. M. Martínez-Tarifa, G. Robles and M. A. Hombrados-Herrera, Ageing study on enameled magnet wires through statistical analysis of conventional partial discharge magnitudes and repetition rate, 2016 IEEE International Conference on Dielectrics (ICD), Montpellier, France, 2016, pp. 650-653. doi: 10.1109/ICD.2016.7547699
Abstract—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.
Keywords—Aging;Fitting;Insulation; Magnetomechanical effects; Mathematical model; Partial discharges;Wires;ageing models;electrical insulation;enamelled magnet wires;partial discharges
M.V. Rojas-Moreno, G. Robles, J. M. Martínez-Tarifa and J. M. Fresno, Ensemble Empirical Mode Decomposition for the denoising of partial discharges measured in UHF, 2016 IEEE International Conference on Dielectrics (ICD), Montpellier, France, 2016, pp. 963-966. doi: 10.1109/ICD.2016.7547777
Abstract—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.
Keywords—Antenna measurements;Partial discharges;Pollution measurement;Radio frequency;Surface discharges;UHF measurements;White noise
J. M. Martínez-Tarifa, J. A. Ardila-Rey, A. Prieto-Duque, J. M. Fresno and G. Robles, Statistical analysis of RF signals emitted by partial discharges, 2016 IEEE International Conference on Dielectrics (ICD), Montpellier, France, 2016, pp. 536-539. doi: 10.1109/ICD.2016.7547660
Abstract—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.
Keywords—Discharges (electric);Dispersion; Partial discharge measurement; Partial discharges;Radio frequency;Surface discharges;Voltage measurement; RF emission; acquisition systems;partial discharge; statistical analysis
L. Lusuardi; A. Cavallini; P. Mancinelli; M. Gómez de la Calle; J.M. Martínez-Tarifa; G. Robles. Design criteria for inverter-fed Type 1 motors. 2016 IEEE International Conference on Dielectrics (ICD), Montpellier, France, 2016, pp. 605-608. doi: 10.1109/ICD.2016.7547528
Abstract—According to the IEC 60034-18-41, the reliability of inverter-fed motor electrical insulation must be assessed through qualification tests with stress levels based on empirical assumptions. For purely organic (Type 1) electrical insulation systems, the inception of partial discharges within the insulation systems is the end-life criterion. The aim of this paper is to start a work in the direction of proposing a framework for designing from scratch motor insulation systems with partial discharge inception voltage adequate for inverter applications. To achieve this purpose, inception voltage estimates obtained using streamer inception criteria were compared with measurements performed in the lab. The results show that, for a large class of magnet wires, conservative estimates can be obtained.
Keywords—IEC Standards;Insulation;Mathematical model;Partial discharges; Qualifications;Voltage measurement;Wires;Inverter-fed machines;Partial discharge
Open access https://sciforum.net/conference/ecsa-2/paper/3217/download/pdf
G. Robles; J.M. Fresno; M. Sánchez-Fernández; J.M. Martínez-Tarifa. Antenna array layout for the localization of partial discharges in open-air substations. In Proceedings of the 2nd Int. Electron. Conf. Sens. Appl., 15–30 November 2015; Sciforum Electronic Conference Series, Vol. 2, 2015, E008; doi:10.3390/ecsa-2-E008
Abstract—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.
Keywords—partial discharges, time difference of arrival, localization, antennas, insulation, maintenance, measurement.
Ardila-Rey, R. Albarracín, J.M. Martínez-Tarifa and G. Robles; On the use of spectral power ratios for partial discharge and noise separation in radiofrequency measurements. 2015 IEEE International Instrumentation and Measurement Techonology Conference, Pisa (Italy), May 11-14, 2015
Abstract—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 toseparate RF signals emitted by PD and noise. Keywords—Vivaldi antenna, spectral power ratios, partial discharges, noise separation and radiofrequency.
García, G. Robles, D F. García; Moisture sensor to characterize solid insulations in transformers under non-equilibrium conditions. 11th IEEE ICSD International Conference on Solid Dielectrics, Bologna (Italy), Jul 1-4, 2013
Abstract—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 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.
Keywords—moisture dinamics; natural esters; diffusion coefficient; transformer load
J.A. Ardila-Rey, J.M. Martínez-Tarifa, M. Mejino, M.V. Rojas-Moreno, G. Robles; Chromatic classification of RF signals for partial discharges and noise characterization. 11th IEEE ICSD International Conference on Solid Dielectrics, Bologna (Italy), Jul 1-4, 2013
Abstract—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.
Keywords—partial discharge, RF emission, acquisition systems, chromatic classification
G. Robles, R. Albarracín, J.L. Vázquez-Roy, E. Rajo-Iglesias, J.M. Martínez-Tarifa, M.V. Rojas-Moreno, M. Sánchez-Fernández; On the use of Vivaldi antennas in the detection of partial discharges. 11th IEEE ICSD International Conference on Solid Dielectrics, Bologna (Italy), Jul 1-4, 2013
Abstract—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 avoidingelectromagnetic noise present at lower frequencies.
Keywords—Antennas measurements, partial discharges, UHF antennas, UHF measurements, dielectric measurements