A power transformer is one of the most important and expensive components in any power system. Power transformers can be exposed to a wide variety of abnormal conditions and faults. Internal turn-to-turn faults are the most difficult types of faults to detect within the power transformer. The IEEE Standards documents have revealed that there is no one standard way to protect all power transformers against minor internal faults such as turn-to-turn faults and at the same time to satisfy basic protection requirements: sensitivity, selectivity, and speed.<p> This thesis presents a new, simple and efficient protection technique which is based on negative sequence currents. Using this protection technique, it is possible to detect minor internal turn-to-turn faults in power transformers. Also, it can differentiate between internal and external faults. The discrimination is achieved by comparing the phase shift between two phasors of total negative sequence current. The new protection technique is being studied via an extensive simulation study using PSCAD®/EMTDC 1 software in a three-phase power system and is also being compared with a traditional differential algorithm.<p> Relay performance under different numbers of shorted turns of the power transformer, different connections of the transformer, different values of the fault resistances, and different values of the system parameters was investigated. The results indicate that the new technique can provide a fast and sensitive approach for identifying minor internal turn-to-turn faults in power transformers.

A power transformer is one of the most important and expensive components in any power system. Power transformers can be exposed to a wide variety of abnormal conditions and faults. Internal turn-to-turn faults are the most difficult types of faults to detect within the power transformer. The IEEE Standards documents have revealed that there is no one standard way to protect all power transformers against minor internal faults such as turn-to-turn faults and at the same time to satisfy basic protection requirements: sensitivity, selectivity, and speed.<p> This thesis presents a new, simple and efficient protection technique which is based on negative sequence currents. Using this protection technique, it is possible to detect minor internal turn-to-turn faults in power transformers. Also, it can differentiate between internal and external faults. The discrimination is achieved by comparing the phase shift between two phasors of total negative sequence current. The new protection technique is being studied via an extensive simulation study using PSCAD®/EMTDC 1 software in a three-phase power system and is also being compared with a traditional differential algorithm.<p> Relay performance under different numbers of shorted turns of the power transformer, different connections of the transformer, different values of the fault resistances, and different values of the system parameters was investigated. The results indicate that the new technique can provide a fast and sensitive approach for identifying minor internal turn-to-turn faults in power transformers.

Le réseau électrique de bord des avions devient le principal vecteur de transmission de l'énergie utilisée en dehors de celle réservée à la propulsion. Le réseau électrique remplace progressivement les réseaux hydrauliques et aérauliques qui assurent respectivement les contrôles de vol et le confort dans la cabine des avions actuels. Pour transmettre une puissance électrique plus importante sans augmenter la masse des conducteurs, un nouveau standard a été défini, le réseau de bord des avions plus électriques sera continu et sa tension est fixée à 540V. En conséquence, les convertisseurs statiques seront systématiquement utilisés pour commander les actionneurs électriques. Des contraintes électriques nettement plus importantes seront appliquées aux bobinages des machines en plus de celles qui sont inhérente à l'aéronautique. Pour obtenir la sureté de fonctionnement requise, la surveillance du vieillissement de l'isolation des machines électriques embarquées devient indispensable. Le travail effectué dans cette thèse est centré sur la définition d’un nouvel indicateur de vieillissement de l’isolation des bobinages des machines électriques utilisées en aéronautique. Le nouvel indicateur delta-C est basé sur la corrélation entre l'augmentation de la capacité inter-spires du bobinage et la réduction des performances caractérisée principalement par la réduction du seuil d'apparition des décharges partielles. La partie expérimentale des travaux est importante; le mémoire donne les résultats des campagnes de vieillissement accéléré d'un grand nombre d'échantillons de fil émaillé standard. Ces résultats permettent de définir des seuils critiques des variations du nouvel indicateur delta-C en fonction du profil de mission de l'actionneur. Le nouvel indicateur delta-C est corrélé avec un paramètre facilement mesurable sur une machine électrique en fonctionnement qui est la fréquence de résonance du bobinage. Un outil numérique est développé pour déterminer les fréquences de résonances à surveiller en fonction de la géométrie et de la technologie du bobinage de la machine. Les prédictions des fréquences déterminées par l'outil numérique développé sont vérifiées par des mesures faites sur des bobines vieillies artificiellement. L'étude est étendue à l'influence du câble d'alimentation de la machine. Les limites de fonctionnement du système de surveillance proposé sont définies pour différentes distances entre la machine et le point de connexion des systèmes de mesure. / For modern aircrafts, the onboard electrical grid becomes the main energy transmission system apart from energy reserved for propulsion. Electrical systems are gradually replacing hydraulic and air systems providing respectively flight controls and cabin comfort in current aircrafts. To transmit higher electrical power without increasing the conductors’ masses, a new standard has been set, the grid of more electrical aircrafts will be 540 VDC. As a result, static converters will systematically be used to drive the electrical actuators. Substantially higher electrical constraints will be applied to electrical machine windings, in addition to those inherent in aeronautics. To obtain the required operational safety, the monitoring of the insulation for onboard electrical embedded machines has become indispensable. This thesis work is focused on the definition of a new aging indicator for the electrical insulation of machine used in aeronautics. The new delta-C indicator is based on the correlation between the increase in the turn-to-turn winding capacitance and reduction of performance mainly characterized by the decrease of Partial Discharge Inception Voltage (PDIV). The experimental part of this work is considerable; the thesis gives the results of accelerated aging tests on a large number of enameled wire standard samples. These results make it possible to define critical threshold for the new delta-C indicator depending on the mission profile of the actuator. The new delta-C indicator is correlated with an easily measurable parameter on an operating electrical machine, i.e. the resonance frequencies of the winding. A numerical tool was developed to determine the resonance frequencies to be monitored according to the geometry and the technology of the winding machine. The prediction frequencies determined by the developed numerical tool have been verified by measurements on artificially aged coils. The study has been extended to the influence of the supply cable of the electrical machine. The operating limits of the proposed monitoring system are defined for various distances between the electrical machine and the connection point of the measurement systems.

In the aviation industry, safety and robustness are the number one priorities, which is why they use well-tested systems such as hydraulic actuators. However, drawbacks such as high weight and maintenance have pushed the industry toward newer, electrical, actuators that are more efficient and lighter. Electrical actuators, on the other hand, have some reliability issues. In particular, short circuits in the stator windings of Permanent-Magnet SynchronousMotors (PMSMs), referred to as Inter-Turn Short Faults (ITSFs), are the dominating faults, and is the focus of this thesis. ITSFs are usually challenging to detect and often do not become noticeable until the fault has propagated, and the motor is on the verge of being destroyed. This thesis investigates the possibility of detecting ITSFs in a PMSM, at an early stage when only one turn is shorted. The method is limited to finding the faults using ML algorithms. Both an experiential PMSM and a simulated model of the experimental PMSM, with the ability to induce an ITSF, were used to collect the data. Several Machine Learning (ML) models were developed, and then trained and tested with the collected data. The results show that four of the tested ML models, being: Random Forest, Gaussian SVM, KNN, and the CNN, all achieve an accuracy exceeding 95%, and that the fault can be found at an early stage in a PMSM with three coils connected in parallel in each phase. The results also show that the ML models are able to identify the ITSF when the simulated data is downsampled to the same frequency as the experimental data. We conclude that the ML models, provided in this study, can be used to detect an ITSF in a simulated PMSM, at an early stage when only one turn is shorted, and that there is great potential for them to detect ITSFs in a physical motor as well.

L’objectif de ce travail est d’élaborer un modèle performant/précis de la machine électrique permettant de proposer une technique de pronostic. Dans cette thèse, nous commençons par un état de l’art sur les véhicules électriques hybrides (VHE), les différents types de machines électriques utilisées dans les VHE ainsi que les différents types de défauts pouvant survenir dans ces machines électriques. Nous identifions également les indicateurs de défauts appropriés aux différents défauts considérés. Ensuite, une synthèse de techniques de pronostic pouvant être appliquées est proposée. Le modèle à éléments finis électromagnétiques, thermiques et vibratoires (FEM) de la machine à aimants permanents est présenté. Le modèle est élaboré en fonctionnement normal et défaillant. Les types de défauts considérés sont : démagnétisation, court-circuit et excentricité. Une comparaison entre les deux approches analytique et FEM (méthode numérique) pour la modélisation de machines électromagnétiques est effectuée. Les indicateurs de défauts analysés pour l’extraction les plus pertinents utilisent les différents signaux mesurées suivants : le couple, la température ainsi que les signaux vibratoires en états sains et défectueux. L’approche de pronostic adoptée qui est le modèle de Markov caché (HMM) est développée. L'aspect technique de la méthode est présenté et le module du pronostic est formulé. La méthode de HMM est utilisée pour détecter et localiser les défauts à petites amplitudes. Une stratégie systématique a été développée. Le vieillissement de l’équipement de la machine, en particulier des éléments sensibles comme la bobine de stator et l’aimant permanent, est une question très importante pour le calcul du RUL (Remaining Useful Life). Une stratégie d’estimation pour le calcul RUL est présentée et discutée. La configuration en boucle fermée est très importante. Elle est adoptée par tous les systèmes de véhicules disponibles. Par conséquent, les mêmes étapes mentionnées précédemment s'appliquent également à une configuration en boucle fermée. Un modèle global où l’entrée du FEM de la machine provient de l’onduleur modélisé est élaboré. / The core of the work is to build an accurate model of the electrical machine where the prognostic technique is applied. In this thesis we started by a literature review on hybrid electric vehicles (HEV), the different types of electrical machine used in HEV’s and the different types of faults that may occur in those electrical machine. We also identify the useful monitoring parameters that are beneficial for those different types of faults. Then, a survey is presented where all the prognostic techniques that can be applied on this application are enumerated. The electromagnetic, thermal and vibration finite element model (FEM) of the permanent magnet machine is presented. The model is built at healthy operation and when a fault is integrated. The considered types of faults are:demagnetization, turn to turn short circuit and eccentricity. A confrontation between analytical and FEM (numerical method) for electromagnetic machine modeling is illustrated. Fault indicators where useful measured parameters forfault identification are recognized and useful features from the measured parameters are extracted; torque, temperature and vibration signal are elaborated for healthy and faulty states. The strategy of the adopted prognostic approach which is Hidden Markov Model (HMM) is explained. The technical aspect of the method is presented and the prognostic model is formulated. HMM is applied to detect and localize small scale fault small scale faults were where a systematic strategy is developed. The aging of the machine’s equipment,specially the sensitive ones that are the stator coil’s and the permanent magnet, is a very important matter for RUL calculation. An estimation strategy for RUL calculation is presented and discussed for those mentioned machine’s components. Closed loop configuration is very important; it is adopted by all available vehicle systems. Hence, the same previously mentioned steps are applied for a closed loop configuration too. A global model where the input of the machine’s FEM comes from the modeled inverter is built.