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Presented at the 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). IEEE Version: 10.1109/CPEM.2018.8500956 ; The work reported here has received support from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

Authors proof of conference paper presented at CPEM 2020, 24-28 Aug., 2020, Denver, CO, USA ; This work has been performed with support from the Swedish Governmental Agency for Innovation Systems.

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. ; Tests were done in the High-Voltage Research and Test Laboratory (LINEALT) at Universidad Carlos III de Madrid. This work has been partly funded by the Spanish Government through projects SI-DP (DPI2015-66478-C2-1), MIMOTEX (TEC2014-61776-EXP) and ELISA (TEC2014-59255-C3-3R).

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. ; The work done in this paper has been funded by the Spanish Government (MINECO) and the European Regional Development Fund (ERDF) under contract DPI2015-66478-C2-1-R (MINECO/FEDER, UE).

The influence of the pressure of the coolant used in high voltage rotating machines on partial discharges occurring in stator insulation is discussed in this paper. The first part deals with a theoretical analysis of the topic. The second part deals with the results obtained on a real generator in industrial conditions. Finally, theoretical assumptions and obtained results are compared.

In the late 19th century, the extraordinary inventors and pioneers Nikola Tesla, Thomas Edison, and George Westinghouse dreamed of transforming the world. After more than a hundred years since then, electricity has not stopped growing and is set to become the largest industrial system created by humanity. The democratization of hybrid and electric cars, and even more the future electrification of the aeronautical industry are signs of its unstoppable evolution. As a system in constant improvement and evolution, it has not been without challenges to overcome without compromising its reliability. One of the phenomena that continues to be a threat and reduces the reliability of machines are partial discharges. These events affect the insulation system and can cause a material failure that can translate into equipment damage, power supply interruption and even incendiary and explosive events. One of the cornerstones that this electrical system relies on is alternating current motors. Spurred on by progress in semiconductors and the discovery of the microprocessor, aging of DC motors have taken over. Since then, the electronic control of these motors has become essential, to the point that for small power rated machines, a single set is sold: "copper, iron and silicon". Unexpectedly, this improved speed control caused a significant reduction in the reliability of the motors, causing unforeseen failures in the insulation systems. Since the turn-to-turn insulation is the Achilles heel for most of these motors, this will be the core subject in this dissertation. This problem has been an ordeal in the way of designers, due to its stochastic nature and the uncertainties associated with the different models proposed in the literature. With the development of this thesis, it is intended to model the phenomenon of partial discharges, combining finite element calculations with the results obtained in laboratory tests, to predict the appearance of partial discharges. Likewise, the impact of the different sources of uncertainty ...

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. ; The work done in this paper has been funded by the Spanish Government (MINECO) and the European Regional Development Fund (ERDF) under contract DPI2015-66478-C2-1-R (MINECO/FEDER, UE).

Pre-print of extended paper published in IEEE TIM based on presentation from CPEM 2020, Denver, USA, Aug 24-28, 2020. ; This project 19ENG02 FutureEnergy has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

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. ; This research has been supported by the Spanish Science and Technology Ministry under contract DPI 2009-14628- C03-02 and by the Madrid Regional Government and Universidad Carlos III de Madrid under contract CCG10- UC3M/DPI-4627. Tests have been made in the High Voltage Research and Tests Laboratory of Universidad Carlos III de Madrid (LINEALT). ; Publicado

Presented at the 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). IEEE Version: 10.1109/CPEM.2018.8501003 ; The work reported here has received support from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

Congreso online, sin sede definida. ABSTRACT: Electrical insulation can have imperfections due to manufacturing or ageing. When the insulation is electrically stressed, partial discharge (PD) pulses, with very fast rise-times and short-time durations, may occur. One of the consequences of charges being accelerated within the discharge is the emission of electromagnetic energy. The measurement of these emissions is widely used to identify defective insulation within high voltage equipment and help in predictive and planned maintenance in order to prevent sudden failure. The location of the source of the radiated PD signals may be determined using multi-lateration techniques using an array of at least four antennas. Depending on the relative position between the antennas and the PD source, the pulsed emissions from the PD source arrive at each antenna at different times. The relative time differences of arrivals (TDOA) together with the antenna positions are variables used to locate the PD source in 3D space. This paper investigates the accuracy of the location determination of the source as a consequence of systematic errors on the positioning of the antennas. These errors are analyzed for three different antenna array configurations and for different vector directions from the arrays. Additionally, the least sensitive layout in relation to antenna positioning errors is proposed to assist in improving the location accuracy of PD sources. ; Simulations were undertaken at the Universidad Carlos III of Madrid and the University of Strathclyde Glasgow. The work undertaken in this paper has been funded by the Spanish Government under contract DPI2015-66478-C2-1. Jose M. Fresno received an international travel grant from the Universidad Carlos III of Madrid.