A partial discharge (PD) is the dissipation of energy caused by the buildup of localized electric field intensity. In high voltage devices such as transformers, this buildup of charge and its release can be symptomatic of problems associated with aging, such as floating components and insulation breakdown. This is why PD detection is used in power systems to monitor the state of health of high voltage transformers. If such problems are not detected and repaired, the strength and frequency of PDs increases and eventually leads to the catastrophic failure of the transformer, which can cause external equipment damage, fires and loss of revenue due to an unscheduled outage. Reliable online PD detection is a critical need for power companies to improve personnel safety and decrease the potential for loss of service. The PD phenomenon is manifested in a variety of physically observable signals including electric and acoustic pulses and is currently detected using a host of exterior measurement techniques. These techniques include electrical lead tapping and piezoelectric transducer (PZT) based acoustic detection. Many modern systems use a combination of these techniques because electrical detection is an older and proven technology and acoustic detection allows for the source to be located when several sensors are mounted to the exterior of the tank. However, if an acoustic sensor could be placed inside the tank, not only would acoustic detection be easier due to the increased signal amplitude and elimination of multipath interference, but positioning could also be performed with more accuracy in a shorter time. This thesis presents a fiber optic acoustic sensing system design that can be used to detect and locate PD sources within a high voltage transformer. The system is based on an optical acoustic (OA) sensor that is capable of surviving the harsh environment of the transformer interior while not compromising the transformer's functionality, which allows for online detection and positioning. This thesis presents the theoretical functionality and experimental validation of a band-limited OA sensor with a usable range of 100-300 kHz, which is consistent with the frequency content of an acoustic pulse caused by a PD event. It also presents a positioning system using the time difference of arrival (TDOA) of the acoustic pulse with respect to four sensors that is capable of reporting the three-dimensional position of a PD to within ±5cm on any axis. / Master of Science

Le but de cette thèse est l'étude et la mise en oeuvre d'un système de localisation sous-marine compact et simple à mettre en place pour une utilisation en zones portuaires, côtières et environnements peu profonds. Nous proposons un système SBL (Small Distance Baseline) avec un nombre réduit de transducteurs (une balise d'émission et deux hydrophones). La configuration géométrique du système étant contraignante (hydrophones proches) la précision du positionnement obtenue par les méthodes classiques est faible. Nous proposons une nouvelle méthode de localisation améliorant la précision. La balise à localiser émet un signal à étalement de spectre. La différence de distance entre les trajets des signaux des hydrophones est mesurée par corrélation. Nous proposons deux boucles de poursuites pour l'estimation conjointe de la fréquence Doppler et du délai entre les signaux reçus. Ces techniques de poursuite basées sur un filtre de Kalman sont implémentées en boucle fermée et ouverte. Les observations TDOA (Time Difference Of Arrival) conduisent à utiliser une technique de localisation hyperbolique. Nous proposons une représentation statistique qui exploite la géométrie de notre système de mesure pour déterminer une zone de localisation probable autour de chaque hyperbole. En utilisant des positions de bateau successives, on construit une densité de probabilité dont le maximum définit la position de la balise. On montre sur données synthétiquesque pour un bruit de mesure réaliste, il est possible de déterminer la position de la balise avec une précision submétrique. Les expérimentations réelles confirment la faisabilité du système et la précision obtenue est dans ce cas métrique. / The purpose of that thesis work is the research and implementation of a compact and simple underwater localization system that aim to be used in ports, coastal areas and other low-depth environments. Our system is SBL (Small Distance Baseline), with a small number of transceivers (only one emitter and two hydrophones). Due to the system's geometric configuration not being optimal (both hydrophones are close to one another), the precision obtained using classical approaches is poor. We therefore propose a new localization approach that will improve it. The emitter we wish to localize emit a spread spectrum signal. The time difference of arrival (TDOA) between the two hydrophones is then determined using correlations methods. We propose in our work two tracking loops that will estimate both the delay and the doppler frequency between the signals. Using a Kalman filter , those methods are implemented respectively in open and close loop. From each TDOA measurement, we can calculatea hyperbolic area of possible emitter location. We thus use a statistical model which takes into account the local geometry of our measurements system in order to create a probable localization area around each hyperbole. By using the measurements at several different boat positions, we create a probability density whose maximum will be centered around the emitter's position. We show that, on simulated data, it is possible to localize the beacon with a precision beneath a meter with a realistic noise level. Experimental work and real data collection confirm that the method can in that context achieve the same result with a precision of a few meters.