High Voltage Insulating Materials-Current State and Prospects

Studies on new solutions in the field of high-voltage insulating materials are presented in this book. Most of these works concern liquid insulation, especially biodegradable ester fluids; however, in a few cases, gaseous and solid insulation are also considered. Both fundamental research as well as research related to industrial applications are described. In addition, experimental techniques aimed at possibly finding new ways of analysing the experimental data are proposed to test dielectrics

Study of oil/pressboard progressive creeping discharge under highly divergent electric field

As one of the most dangerous failure modes of transformers, the oil/pressboard progressive creeping discharge, as well as the corresponding insulation failure mechanisms, have thus far not been fully understood. The present thesis aims to gain a sound fundamental knowledge of the progressive creeping discharge, their influential factors, and the relevant failure mechanisms, as well as to contribute to an effective monitoring and diagnostic methodology. This study explored the progressive creeping discharges under highly divergent AC and DC voltages, respectively. The tests conditions were configured to investigate the impacts of critical influential factors, including ageing, voltage level, temperature, stress waveform, and oil flowing, on creeping discharges. The discharge processes were systematically evaluated using tools such as partial discharge, gas analysis, temperature monitoring, and finite-element simulation. Comparative analyses and theoretical examinations were made to the insulation faults as well as their correlated physicochemical phenomena. A conventional techniques-based monitoring framework was proposed for the dangerous creeping discharges, and the applicability of a new detection technique based on synchronous PD and dielectric measurements was tested as well. The characteristics of damage-free AC progressive creeping discharge, as well as the influences of pressboard ageing and field intensity, were investigated. It was found the progressive creeping discharge is a compound discharge that comprises mainly oil corona discharge and surface discharge. Pressboard ageing affected the discharge inception but had no influence on the interface breakdown strength. The damage-free discharge exhibited a constant PRPD pattern but had a diminishing PD intensity, where the pressboard ageing and voltage level jointly determine whether the discharges can be sustained or not. The damage-free discharge generated hydrogen principally and was located between D1/ D2 fault zones in the classical Duval’s Triangle. The insulation failures due to dangerous creeping discharges were comparatively studied. It was found the AC progressive creeping discharge could generate two faults to the pressboard, i.e., internal treeing (internal treeing) and surface tracking (surface tracking). The faults exhibited distinct electrical as well as physicochemical characteristics, and their occurrences were subject to pressboard ageing, voltage level, and pressboard density. A four-staged model was proposed to illustrate the development of internal treeing. The model highlighted the central role of the filament-like carbonization tracks in the pressboard interior, of which the onset and growth were theoretically expounded as well. A detection methodology was proposed for internal treeing, which was mainly based on continuous PD measurement, online temperature monitoring, and gas analysis. However, it was found still hard to detect a severe surface tracking fault due to the PD disappearance. The influences of temperature and voltage waveforms on AC progressive creeping discharge were studied. Temperature affected the short-time electric strength of either interface or oil gap and could form a synergistic effect with a strong field in exacerbating the dissipation factor of pressboard. Moreover, it was found temperature can determine the fault types and discharge severity under either constant or step-wise stress, whereas the stress waveform had an obvious effect on the fault type only at high temperatures. Depending on the test temperature and stress waveforms, the test specimens failed due to tracking-free interface flashover, surface tracking, and internal treeing, respectively. Their PD quantities were comparatively evaluated. Moreover, it was found the synchronous PD and dielectric measurement is highly indicative of the internal treeing process, and it exhibited both high detection sensitivity and discharge identification capability. The DC progressive creeping discharge was evaluated against temperatures and forced oil flows. Temperature affected the DC conductivity of both oil and pressboard, the resistivity ratio of pressboard to oil, and the oil/pressboard interface charge relaxation time. Accordingly, the interface field distributions were evaluated against temperatures using the finite-element method. Moreover, both oil flow speed and temperatures affected the short-time DC interface electric strength as well as the progressive creeping discharge. Two types of discharges were found under static oil condition. They exhibited distinct PD characteristics and showed different responses to temperature changes. They were presumably associated with discharges in oil and pressboard, respectively. Furthermore, it was found that forced oil flows can alter the behaviors of DC creeping discharges drastically and generated a peculiar PD type (Pulse Train). The occurrence of the pulse train was subject to applied voltage level, temperature, and oil flowing velocity. A theoretical model was proposed to elucidate the pulse train, in which the interactions between space charges from different sources were discussed against voltage levels, oil flows, and temperatures. The present thesis extends the knowledge of the oil/pressboard progressive creeping discharges. The research results are expected to serve as a base for future scientific studies and a piece of reference information for practical applications pertinent to progressive creeping discharges.Eine der gefährlichsten Fehlerarten in Transformatoren, die fortschreitende Kriechentladung in Öl/Feststoff Anordnungen sowie der dazugehörige Mechanismus des Isolationsfehlers sind noch nicht völlig geklärt. Die vorliegende Arbeit zielt auf die Erreichung einer soliden fundamentalen Kenntnis der fortschreitenden Kriechentladung, ihrer Einflussfaktoren und der entsprechenden Fehlermechanismen ab. Weiterhin soll sie einen Beitrag zur effektiven Überwachung und diagnostischen Methoden liefern. Die Untersuchungen beinhalten die fortschreitenden Kriechentladungen bei stark inhomogenen elektrischen Feldern unter Wechsel- und Gleichspannung. Die Versuchsbedingungen wurden so konfiguriert, dass die Wirkung der kritischen Einflussfaktoren auf die Kriechentladungen wie Alterung, Höhe der Spannung, Temperatur, Beanspruchungsform und Ölfluss, untersucht werden konnte. Die Entladungsvorgänge wurden systematisch ausgewertet unter Verwendung von Methoden wie Teilentladung, Gasanalyse, Temperaturerfassung und Simulation mit Finiten Elementen. Vergleichende Analysen und theoretische Prüfungen wurden im Hinblick auf Isolierungsfehler und der dazugehörigen physio-chemischen Erscheinungen durchgeführt. Ein auf konventioneller Technik basierendes Monitoring Konzept wurde für die gefährlichen Kriechentladungen vorgeschlagen und die Anwendung neuer Detektionstechniken basierend auf synchroner Teilentladungserfassung und dielektrischen Messungen geprüft. Die Eigenschaften von beschädigungsfreien fortschreitenden Kriechentladungen bei Wechsel-spannung und der Einfluss der Alterung des Pressspan sowie der Feldstärke wurden untersucht. Es wurde herausgefunden, dass die fortschreitende Kriechentladung eine zusammengesetzte Entladung ist, bestehend aus Korona-Entladungen in Öl und Oberflächenentladungen. Die Alterung von Pressspan beeinflusst den Einsatz der Entladung aber hat keinen Einfluss auf die Durchschlagsfestigkeit der Grenzfläche. Die beschädigungsfreie Entladung zeigt ein konstantes PRPD Muster aber mit abnehmender Teilentladungs-Aktivität, wobei die Alterung des Pressspans und die Spannungshöhe gemeinsam bestimmen, ob die die Entladungen unterbrochen werden oder nicht. Die beschädigungsfreie Entladung erzeugt grundsätzlich Wasserstoff und ist den Fehlerzonen D1/D2 des klassischen Duval Dreiecks zugeordnet. Die Fehler der Isolierung infolge der gefährlichen Kriechentladungen wurden vergleichend untersucht. Es wurde herausgefunden, dass die fortschreitende Kriechentladung bei Wechselspannung zwei Fehlerarten im Pressspan erzeugen kann, die schnelle Kriechwegbildung (internes Treeing) und die langsame Kriechwegbildung (Oberflächen Kriechweg). Die Fehler weisen deutlich elektrische als auch physio-chemische Eigenschaften auf und ihr Erscheinen war abhängig vom Alterungszustand des Pressspans, Spannungshöhe und Dichte des Pressspans. Ein vierstufiges Modell wurde vorgeschlagen um die Entwicklung der schnellen Kriechwegbildung darzustellen. Das Modell betont die zentrale Rolle der faserähnlichen karbonisierten Kriechwege im Inneren des Pressspans, wobei Einsatz und Wachstum theoretisch erklärt werden. Eine Erkennungsmethode für die Schnelle Kriechwegbildung wurde vorgeschlagen, die im Wesentlichen auf Teilentladungsmessungen, online Temperaturerfassung und Gas Analyse basiert. Es war dennoch schwierig eine langsame Kriechwegbildung zu erfassen, da Teilentladungen verschwanden. Die Einflüsse von Temperatur und Spannungsform auf fortschreitende Kriechwegentladungen wurden untersucht. Die Temperatur beeinflusste die kurzzeitige elektrische Feldstärke der Grenzschicht und der Ölstrecke und kann eine synergetische Auswirkung mit einem starken Feld auslösen, indem sich der Verlustfaktor des Pressspans erhöht. Es wurde weiterhin herausgefunden, dass die Temperatur die Fehlertypen und Entladungsstärke unter konstanter oder stufenweise Beanspruchung beeinflussen kann, wobei die Art der Beanspruchung einen klar erkennbaren Einfluss auf die Fehlerart nur bei hohen Temperaturen hat. Abhängig von der Prüftemperatur und der Beanspruchungsforme versagten die Prüflinge durch Grenzschichtüberschlag ohne Kriechwegspuren, langsame Kriechwegbildung und schnelle Kriechwegbildung. Ihre Teilentladungsgrößen wurden vergleichend ausgewertet. Darüber hinaus wurde herausgefunden, dass synchrone Teilentladungen und dielektrische Messungen eine gute Kennzeichnung für schnelle Kriechwegbildungsprozesse sind und es zeigt die Fähigkeit einer hohen Erkennungsempfindlichkeit und Entladungserkennung. Die fortschreitenden Kriechentladungen bei Gleichspannung wurden in Abhängigkeit der Temperatur und der Ölflussstärke ermittelt. Die Temperatur beeinflusst die Gleichspannungsleitfähigkeit von beiden, Öl und Pressspan, das Widerstandsverhältnis von Pressspan und Öl, und die Relaxationszeit der Grenzschichtladungen Öl/Pressspan. Dementsprechend wurde die Grenzschichtfeldverteilung in Abhängigkeit der Temperatur mit Hilfe der Finite-Elemente Methode ausgewertet. Außerdem beeinflussten die Geschwindigkeit des Ölflusses und die Temperaturen die kurzzeitige Grenzflächenfeldstärke bei Gleichspannung und fortschreitenden Kriechwegentladung. Zwei Arten von Entladungen wurde bei ruhendem Öl gefunden. Sie zeigen deutliche Teilentladungsmerkmale und unterschiedliches Verhalten bei Temperaturänderungen. Sie waren vermutlich verbunden mit Entladungen im Öl und Pressspan. Es wurde weiterhin herausgefunden, dass forcierte Ölströmung das Verhalten der Kriechentladungen bei Gleichspannung drastisch verändert und einen besonderen Typ von Teilentladungen erzeugt (Pulsfolge). Die Erscheinung dieser Pulsfolge war abhängig von der Höhe der angelegten Spannung, der Temperatur und der Geschwindigkeit des Ölflusses. Es wurde ein theoretisches Modell zur Verdeutlichung der Pulsfolge vorgeschlagen, bei dem die Wechselwirkungen zwischen Raumladungen von verschiedenen Quellen behandelt wurden in Abhängigkeit der Spannungshöhe, des Ölflusses und der Temperatur. Die vorliegende Arbeit erweitert die Kenntnis der fortschreitenden Kriechentladungen in der Anordnung Öl/Pressspan. Es wird erwartet, dass die Untersuchungsergebnisse als Basis für zukünftige wissenschaftliche Studien dienen und einen Beitrag mit hinweisenden Informationen für die praktische Anwendung zur Thematik fortschreitender Kriechentladungen liefern

Self-powered, long-durable, and highly selective oil–solid triboelectric nanogenerator for energy harvesting and intelligent monitoring

Triboelectric nanogenerators (TENGs) have potential to achieve energy harvesting and condition monitoring of oils, the “lifeblood” of industry. However, oil absorption on the solid surfaces is a great challenge for oil–solid TENG (O-TENG). Here, oleophobic/superamphiphobic O-TENGs are achieved via engineering of solid surface wetting properties. The designed O-TENG can generate an excellent electricity (with a charge density of 9.1 µC m−2 and a power density of 1.23 mW m−2), which is an order of magnitude higher than other O-TENGs made from polytetrafluoroethylene and polyimide. It also has a significant durability (30,000 cycles) and can power a digital thermometer for self-powered sensor applications. Further, a superhigh-sensitivity O-TENG monitoring system is successfully developed for real-time detecting particle/water contaminants in oils. The O-TENG can detect particle contaminants at least down to 0.01 wt% and water contaminants down to 100 ppm, which are much better than previous online monitoring methods (particle > 0.1 wt%; water > 1000 ppm). More interesting, the developed O-TENG can also distinguish water from other contaminants, which means the developed O-TENG has a highly water-selective performance. This work provides an ideal strategy for enhancing the output and durability of TENGs for oil–solid contact and opens new intelligent pathways for oil–solid energy harvesting and oil condition monitoring

The influence of electric charge and electric fields on the formation and duration of water boules

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Consideration is given to the conditions under which floating drops of water, here referred to as water boules, form, exist and coalesce. Particular emphasis is placed on the part played by electric charge and electric fields in these processes. The literature is reviewed in terms of both the phenomenon of floating drops and of the development of hydrostatics, hydrodynamics and electrohydrodynamics as applicable to the subject. . Experimental investigations to ascertain the boundary conditions to the influence of such electrical forces are described, together with observations of the connected electrical events. It is confirmed that boules will fail to form at all, i) under conditions of high humidity, and ii) in the presence of an electric field greater than a certain value. This is investigated experimentally, and shown to be approximately 34kV/m, this figure being about two-thirds that previously reported. Boules traversing a plane water surface are demonstrated to acquire additional charge in the process. In the case of drops dispensed from a grounded source, forming boules and crossing a bulk water surface some 15cm wide, the additional charge gathered is significant. Boules of 0.055g mass were found to have a mean charge of 1.6 x 10-12C on leaving a water surface, having arrived as drops with an average charge of 5.8 x 10-14C. Possible charging mechanisms are discussed. The origin of the initial drop charge is considered, and measurements of this are presented from (i), conventional Faraday cup determinations, and (ii), induction methods applied to free-falling drops. Experimental investigation of the time-dependent electrical records of the coalescence of a dispensed drop with a plane water surface shows the whole coalescence process to have a two-part form. This detail is commonly hidden within more conventional charge-transfer measurements. For the coalescences investigated experimentally an small initial event is shown to occur, involving a charge transfer in the range 1.2 – 4.8 x 10-12C. Oscillograms taken from a large number of coalescences show this preliminary event to be a general feature of the coalescence process, with a number of such traces being appended to the thesis. This initial event is followed by a larger one where the signs of the signals from the drop and the bulk surface are opposite to those of the initial event, and whose potential magnitude is broadly in agreement with that anticipated by double layer disruption. The interfacial potential difference necessary for the onset of instability and subsequent coalescence in the case of closely opposed drops is shown to be dependent on the relative humidity of the ambient air. Consideration is given to G I Taylor’s equation describing the critical potential for the onset of instability between closely spaced drops, and this is shown experimentally to require correction for different humidities. It is demonstrated that the critical potential, Vc, at a relative humidity of 100% is approximately 50% of that at 40% RH. Possible reasons for this are discussed, drawing attention to the problem of establishing an accurate DC relative permittivity value for vapour-laden air in small interfacial gaps. The rôle of evaporation in modifying the system geometry is considered experimentally and theoretically, and shown to be significant only for humidities < 50%. The complex nature of the interface in the case of very small air-gaps is discussed, together with the implications of these investigations for the interfacial stability of a floating drop or boule system. A theoretical model based on a consideration of the complex liquid-air-liquid interface as a capacitive system is developed, and shown to be in good agreement with practical observations. This model demonstrates that the parts played by electrical forces, together with environmental factors, are likely to be significant in terms of coalescence at stages prior to gap thinning to the point where London/van-der-Waals forces become dominant. Interfacial potentials are calculated in a boule system at a number of times between 0.1 and 10 seconds, and shown to be sufficient to promote instability and coalescence. Full data based on a number of values of instability potentials is appended to the thesis. Development of the model raises questions concerning the validity of currently accepted values both for interfacial stability in small gaps and for the relative permittivity of humid air in similar situations. Suggestions are made for future work in such areas, together with possible methodologies. The phenomenon of floating water drops is therefore shown to be compatible with the general coalescence process, the event time being modified by such diverse factors as the impact energy with the surface, the ambient humidity and the magnitude of the initial drop charge. The latter is shown to be the dominant factor in the case of drops arriving on a clean surface with low kinetic energies, with the small charge inherent on any water drop being sufficient to produce potentials adequate to promote eventual instability

Transformer design considerations utilising natural ester oils.

Master of Science in Engineering. University of KwaZulu-Natal, Durban, 2015.As modern day transformer designs are gradually moving towards an eco-friendly alternate insulation medium, this dissertation is focussed on the modelling of a typical 88/6.6 kV 20 MVA high voltage winding in both FEMM and COMSOL software packages to where the thermal and dielectric the performance of mineral and ester oil were assessed. For the dielectric analysis, Finite Element Model (FEM) software was utilised and electric field stress measurements (long and short gap) were taken between the windings, paper and pressboard for both ester and mineral oil. Results showed that for natural ester oil, the electrical stresses were concentrated in the paper as opposed to mineral oil where the stresses are more concentrated in the oil. Also a comparison between thermally upgraded (higher permittivity) and standard kraft paper yielded a 1 kV/mm reduction in electric stress for the upgraded kraft paper. This means that transformers with natural ester oil will require more insulation on the windings and greater distances between live and ground paths. For the thermal analysis, the material used was mineral oil and ester oil, with the latter having a higher viscosity. The results indicate that the cooling of the transformer is highly dependent on the velocity of the fluid (thermal transfer through convection). The study showed that for the same inlet velocity of fluid the velocities differed slightly due to the viscosity, but they ultimately had a similar thermal performance. The entire transformer, including radiators, would need to be considered to determine the correct flow and thermal performance for the ester

Design, taking into account the partial discharges phenomena, of the electrical insulation system (EIS) of high power electrical motors for hybrid electric propulsion of future regional aircrafts

La réduction des émissions de CO2 est un enjeu majeur pour l'Europe dans les années à venir. Les transports sont aujourd'hui à l'origine de 24% des émissions globales de CO2. L'aviation ne représente que 2% des émissions globales de CO2. Cependant, le trafic aérien est en pleine expansion et, déjà, des inquiétudes apparaissent. A titre d'exemple, en Suède, depuis les années 1990, les émissions de CO2 dues au trafic aérien ont augmenté de 61%. Ce constat explique l'apparition du mouvement "Flygskam" qui se repend dans de plus en plus de pays Européen. C'est dans ce contexte que l'Union Européenne a lancé en septembre 2016 le projet Hybrid Aircraft Academic research on Thermal and Electrical Components and Systems (HASTECS). Le consortium regroupe différents laboratoires et Airbus. Ce projet s'inscrit dans le programme "Clean Sky 2" qui vise à développer une aviation plus verte. L'objectif ambitieux est de réduire de 20% les émissions de CO2 et le bruit produits par les avions d'ici 2025. Pour cela, le consortium étudie une architecture hybride de type série. La propulsion est assurée par des moteurs électriques. Deux cibles ont été définies. En 2025, les moteurs doivent atteindre une densité de puissance de 5kW/kg, système de refroidissement inclus. En 2035, la densité de puissance des moteurs sera doublée pour atteindre 10kW/kg. Pour atteindre ces cibles, le niveau de tension sera considérablement augmenté, au-delà du kilovolt. Le risque de décharges électriques dans les stators des moteurs électriques est considérablement accru. L'objectif de cette thèse est de mettre au point un outil d'aide au design du Système d'Isolation Electrique (SIE) primaire du stator de moteur électrique piloté par convertisseur. Elle est découpée en cinq parties. La première partie commence par préciser les enjeux et défis d'une aviation plus verte. Le SIE du stator de moteur électrique est développé. Enfin, les contraintes qui s'appliquent sur le SIE dans l'environnement aéronautique sont identifiées. La deuxième partie présente les différents types de décharges électriques que l'on peut retrouver. Le principal risque vient des Décharges Partielles (DP) qui détériorent peu à peu le SIE. Le principal mécanisme pour expliquer l'apparition des DP est l'avalanche électronique. Le critère de Paschen permet d'évaluer le Seuil d'Apparition des Décharges Partielles (SADP). Différentes techniques permettent de détecter et mesurer l'activité des DP. Des modèles numériques permettent d'évaluer le SADP. La troisième partie présente une méthode originale pour déterminer les lignes de champ électrique dans un problème électrostatique. Elle n'utilise qu'une formulation en potentiel scalaire. La quatrième partie présente une étude expérimentale pour établir une correction du critère de Paschen. Un bobinage de moteur électrique est très loin des hypothèses dans lesquelles ce critère a été originellement défini. Enfin, la cinquième partie est consacrée à l'élaboration de l'outil d'aide au design du SIE. Des abaques sont construites afin de fournir des recommandations sur le dimensionnement des différents isolants dans une encoche de stator. Une réduction du SADP due à une variation combinée de la température et de la pression est prise en compte.Reducing CO2 emissions is a major challenge for Europe in the years to come. Nowadays, transport is the source of 24% of global CO2 emissions. Aviation accounts for only 2% of global CO2 emissions. However, air traffic is booming and concerns are emerging. For instance, CO2 emissions from air traffic have increased by 61% in Sweden since the 1990s. This explains the emergence of the "Flygskam" movement which is spreading in more and more European countries. It is in this context that the European Union launched in September 2016 the project Hybrid Aircraft Academic research on Thermal and Electrical Components and Systems (HASTECS). The consortium brings together different laboratories and Airbus. This project is part of the program "Clean Sky 2" which aims to develop a greener aviation. The ambitious goal is to reduce CO2 emissions and the noise produced by aircraft by 20% by 2025. To do that, the consortium is studying a serial hybrid architecture. Propulsion is provided by electric motors. Two targets are defined. In 2025, the engines must reach a power density of 5kW/kg, including the cooling system. In 2035, the power density of the engines will be doubled to reach 10kW/kg. To reach these targets, the voltage level will be considerably increased, beyond one kilovolt. The risk of electric discharges in the stators of electric motors is considerably increased. The objective of this thesis is to develop a tool to assist in the design of the primary Electrical Insulation System (EIS) of the stator of an electric motor controlled by a converter. It is organized in 5 parts. The first part begins by clarifying the issues and challenges of a greener aviation. The electric motor stator EIS is developed. Finally, the constraints that apply to the EIS in the aeronautical environment are identified. The second part presents the different types of electric discharges that can be found. The main risk comes from Partial Discharges (PD) which gradually deteriorate the EIS. The main mechanism for explaining the appearance of PD is the electronic avalanche. The Paschen criterion makes it possible to evaluate the Partial Discharge Inception Voltage (PDIV). Different techniques are used to detect and measure the activity of PD. Numerical models are used to evaluate the PDIV. The third part presents an original method for determining the electric field lines in an electrostatic problem. It only uses a scalar potential formulation. The fourth part presents an experimental study to establish a correction of the Paschen criterion. An electric motor winding is very far from the hypotheses in which this criterion was originally defined. Finally, the fifth part is devoted to the development of the SIE design aid tool. Graphs are generated to provide recommendations on the sizing of the various insulators in a stator slot. A reduction in the PDIV due to a combined variation in temperature and pressure is taken into account

Smart operation of transformers for sustainable electric vehicles integration and model predictive control for energy monitoring and management

The energy transmission and distribution systems existing today are stillsignificantly dependent on transformers,despite beingmore efficient and sustainable than those of decadesago. However, a large numberof power transformers alongwith other infrastructures have been in service for decades and are considered to be in their final ageing stage. Anymalfunction in the transformerscouldaffect the reliability of the entire electric network and alsohave greateconomic impact on the system.Concernsregardingurban air pollution, climate change, and the dependence on unstable and expensive supplies of fossil fuels have lead policy makers and researchers to explore alternatives to conventional fossil-fuelled internal combustion engine vehicles. One such alternative is the introduction of electric vehicles. A broad implementation of such mean of transportation could signify a drastic reduction in greenhouse gases emissions and could consequently form a compelling argument for the global efforts of meeting the emission reduction targets. In this thesis the topic of a high penetration of electric vehicles and their possible integration in insular networksis discussed. Subsequently, smart grid solutions with enabling technologies such as energy management systems and smart meters promote the vision of smart households, which also allows for active demand side in the residential sector.However, shifting loads simultaneously to lower price periods is likely to put extra stress on distribution system assets such as distribution transformers. Especially, additional new types of loads/appliances such as electric vehicles can introduce even more uncertaintyon the operation of these assets, which is an issue that needs special attention. Additionally, in order to improve the energy consumption efficiencyin a household, home energy management systems are alsoaddressed. A considerable number ofmethodologies developed are tested in severalcasestudies in order to answer the risen questions.Os sistemas de transmissão e distribuição de energia existentes hoje em dia sãosignificativamente dependentes dos transformadores, pese embora sejammais eficientes e sustentáveis do que os das décadas passadas. No entanto, uma grande parte dos transformadores ao nível dadistribuição, juntamente com outras infraestruturassubjacentes, estão em serviço há décadas e encontram-se nafasefinal do ciclo devida. Qualquer defeito no funcionamento dos transformadorespode afetara fiabilidadede toda a redeelétrica, para além de terum grande impactoeconómico no sistema.Os efeitos nefastos associadosàpoluição do arem centro urbanos, asmudançasclimáticasea dependência de fontes de energiafósseis têm levado os decisores políticos e os investigadores aexplorar alternativas para os veículos convencionais de combustão interna. Uma alternativa é a introdução de veículos elétricos. Umaampla implementação de tal meio de transporte poderia significar uma redução drástica dos gases de efeito de estufa e poderiareforçar os esforços globais para ocumprimento das metas de redução de emissõesde poluentes na atmosfera.Nesta tese é abordado o tema da elevada penetração dos veículos elétricose a sua eventual integração numarede elétricainsular. Posteriormente, são abordadas soluções de redeselétricasinteligentes com tecnologias específicas, tais como sistemas de gestão de energia e contadores inteligentes que promovamo paradigmadas casas inteligentes, que também permitem a gestão da procura ativano sector residencial.No entanto, deslastrando significativamente as cargaspara beneficiar de preçosmais reduzidosé suscetíveldecolocarconstrangimentosadicionaissobre os sistemas de distribuição, especialmentesobre ostransformadores.Osnovos tipos de cargas tais como os veículos elétricospodem introduzir ainda mais incertezassobre a operação desses ativos, sendo uma questão que suscitaespecial importância. Além disso, com ointuitode melhorar a eficiência do consumo de energia numa habitação, a gestão inteligente daenergia é um assunto que também éabordadonesta tese. Uma pletora de metodologias é desenvolvida e testadaemvários casos de estudos, a fim de responder às questões anteriormente levantadas