Localización de Fuentes de Descargas Parciales en Instalaciones Eléctricas

CIGRÉ WORKSHOP: MONTORIZACIÓN DE LÍNEAS – COMITÉS DE ESTUDIO B1 y B2

UNIVERSIDAD DE CANTABRIA – 27 de abril de 2017

José Manuel Fresno, Guillermo Robles, y Juan Manuel Martínez-Tarifa.  E-Mails: jfresno@ing.uc3m.es, grobles@ing.uc3m.es y jmmtarif@ing.uc3m.es.

Departamento de Ingeniería Eléctrica. Universidad Carlos III de Madrid, Avda. Universidad, 30, 28911, Leganés, Madrid, España

Enlace al póster.

Motivación

  • La medida de descargas parciales (DP) permite llevar a cabo un mantenimiento predictivo en instalaciones eléctricas.
  • Las DP emiten una radiación electromagnética que puede ser medida con antenas para la localización de la fuente sin interrumpir el servicio de la instalación.

Método

  • Actualmente, se usan al menos cuatro antenas situadas en distintos puntos para la localización de la fuente de DP.
  • Calculando la diferencia de los tiempos de llegada \tau_{ij} de la emisión a las antenas, y minimizando la función objetivo F se puede estimar la posición \hat{P}_s de la fuente de DP.

Planteamiento

  • Se puede localizar fuentes de DP con sólo dos antenas siguiendo el procedimiento propuesto en este póster:
  • Para calcular la dirección (azimut y elevación) de la fuente de DP se deben orientar las antenas maximizando \tau_{12} y tomar datos en varias posiciones.Imagen4.pngImagen3
  • La distancia entre antenas se mantiene contante e igual a 2 m. Como la velocidad de propagación es c=3\times10^8 m/s, el máximo \tau_{12} es TDoA=2/c =6,67 µs.
  • La posición de la fuente de DP se define como la intersección de las direcciones calculadas en las posiciones donde se realizan las medidas.

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Instrumentación

  • Sistema de adquisición de señales de dos canales basado en una FPGA con un ADC de bajo coste.
  • Antenas monopolo omnidireccionales adaptadas para medir en la banda de frecuencias de las DP.

Discusión

  • La nueva metodología permite localizar fuentes de DP con un sistema de adquisición de dos canales en lugar de cuatro.
  • La reducción de canales de adquisición reduce el precio y el peso del sistema de adquisición.

Conclusiones

  • Es posible localizar fuentes de DP con un sistema de adquisición de dos canales.
  • Ubicando este equipo y las dos antenas en un vehículo aéreo no tripulado, se podría mejorar la exactitud de las medidas y por tanto de la localización.

Spatial study of the uncertainties in the localization of partial discharges for different antenna layouts

Fresno, J.; Robles, G.; Martinez-Tarifa, J.; Stewart, B.; Spatial study of the uncertainties in the localization of partial discharges for different antenna layouts. 2017 IEEE International Instrumentation and Measurement Techonology Conference, Torino (Italy), May 22-25, 2017

https://doi.org/10.1109/I2MTC.2017.7969802

Abstract—The maintenance of high-voltage equipment is paramount to avoid blackouts or the interruption of electrical service. One of the most reliable methods to know the status of insulation systems is the measurement of partial discharges (PD). This phenomenon occurs when the dielectric presents imperfections due to ageing and degradation processes. Partial discharges are sudden releases of charge that can emit energy in a wide band of frequencies even in UHF. Therefore, antennas can be used, not only to detect the occurrence of PD, but to locate the source of emission and, consequently, the damaged asset. The localization can be done using multilateration measuring the time-differences of arrival (TDOA) of the pulses to an array of antennas. However, the onset of the signal is difficult to define due to numerous issues, from low signal-to-noise ratio, to lack of line-of-sight or errors in the positioning of the antennas. Then, the position of the source may have large uncertainties that even can prevent finding the asset at stake. The configuration of the antenna layout can help to minimize the effect of the uncertainties in the measurement of the TDOA. It has been found that there are configurations that favour certain bearings when locating the source giving more accurate results. This paper explores three type of antenna layouts and devises a method to determine what directions are best to orient the array.

Keywords—Antennas, Radio-frequency, Localization, Partial Discharges.

A survey of time-of-flight algorithms to determine bone positions in movement

Fresno, J.; Giannetti, R; Robles, G. A survey of time-of-flight algorithms to determine bone positions in movement. 2017 IEEE International Instrumentation and Measurement Techonology Conference, Torino (Italy), May 22-25, 2017

https://doi.org/10.1109/I2MTC.2017.7969710

Abstract—In biomechanical applications where an ultrasound signal is used to determine the position of a specific organ or tissue, like for example a bone, a so-called A-mode ultrasonography is used. A ultrasonic pulse is generated by a transducer, injected in the tissue to be examined, and then the echoes are received and processed. Echoes are generated by changes in acoustic impedance in the medium, like for example a change of tissue from muscle to bone. To determine the position of the reflecting interface, the time-of-flight is measured and, utilizing well-know values for the transmission speed, the distance or depth is computed. If the localization device is to be designed to be small, wearable, and low-power, it is expected that the signal will be of worse quality with respect to traditional ultrasonography systems, especially under the point of view of signal-to-noise ratio. In these conditions, the reliability of the algorithm that implement the time-of-flight calculation is of paramount importance. In this paper, a simulated soft tissue–bone interface (implemented with an ultrasound gel-pad) has been measured with intentionally low excitation signals and with the presence of imperfections similar to those expected in a physiological system. Several classic algorithms have been tested and benchmarked in this condition, and a new method with better reliability and repeatability is proposed.

Keywords—Time-of-flight, ultrasonic sensors, biomecanical systems, cross-correlation, kurtosis.

The influence of antenna positioning errors on the radio-frequency localization of partial discharges sources

Open access: http://www.mdpi.com/2504-3900/1/2/12/

Fresno, J.; Robles, G.; Stewart, B.; Martinez-Tarifa, J. The influence of antenna positioning errors on the radio-frequency localization of partial discharges sources. In Proceedings of the 3rd Int. Electron. Conf. Sens. Appl., 15–30 November 2016; Sciforum Electronic Conference Series, Vol. 3, 2016 , E003; doi:10.3390/ecsa-3-E003

Abstract—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.

Keywords—Radio-Frequency Localization; Partial Discharges; Antennas Positioning; Measurement Error.

High frequency inductive energy harvester for the maintenance of electrical assets

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.

Ageing study on enameled magnet wires through statistical analysis of conventional partial discharge magnitudes and repetition rate

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

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

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

Statistical analysis of RF signals emitted by partial discharges

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

Design criteria for inverter-fed Type 1 motors

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

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

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.