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Unbroken gel and residue from guar-based fracturing gels can be a cause for formation damage. The effectiveness of a fracturing treatment depends on better achieveing desired fracture geometry, proper proppant placement and after that, a good clean-up. The clean-up is achieved by reducing the fluid viscosity using chemical additives called "Breakers". There are many different types of breakers used in the industry, but they can be broadly divided into two categories: oxidizers and enzymes. Breaker perfromance depends on bottomhole temperature, breaker concentration and polymer loading. Different kind of breakers, used at different concentrations and temperatures, give different kind of "break" results. Therefore, the amount of unbroken gel and residue generated is also different. This project was aimed at studying basic guar-breaker interactions using some of the most common breakers used in the industry. The breakers studied cover a working temperature range of 75 degrees F to 300 degrees F. The effectiveness of each breaker was studied and also the amount of damage that it causes. Viscosity profiles were developed for various field concentrations of breakers. The concentrations were tested over temperature ranges corresponding to the temperatures at which each breaker is used in the field. The majority of these viscosity tests were 6 hours long, with a few exceptions. Early time viscosity data, for the intial 10 minutes of the test, was also plotted from these tests for fracturing applications where the breaker is required to degrade the fluid by the time it reached downhole. This was needed to prevent the damage to the pumping equipment at the surface yet still have almost water-like fluid entering into the formation. The study provides a better understanding of different breaker systems, which can be used in the industry, while designing fracturing fluid systems in order to optimize the breaker performance and achieve a better, cleaner break to minimize the formation damage caused by polymer degradation.

Circuit breakers are used in the power system to break or make current flow through power apparatus. Reliable operation of circuit breakers is critical to the well- being of the power system and can be achieved by regular inspection and maintenance. A low-cost automated circuit breaker monitoring system is developed to monitor circuit breaker control signals. An interface is designed on top of which different local and system-wide applications can be developed which utilize the data recorded by the system. Some of the possible applications are proposed. Lab and field evaluation of the designed system is performed and results are presented.

Different HVDC grid types and the respective protection options are discussed. An earthed bi-pole HVDC grid was modeled in PSCAD, and using simulation results, the necessity of di/dt limiting inductors to contain the rise of fault currents within the capacity of current hybrid DC breakers is demonstrated. The impact of different inductor sizes on current rise was studied. A fault detection and localization scheme using the rate of change of voltage (ROCOV) measured at the line side of the di/dt limiting inductors is proposed. The protection system was modeled and tested under different fault types and locations. The results show that the proposed method of HVDC grid protection is feasible using the current hybrid DC breaker technology. A systematic procedure for setting the necessary protection threshold values is also demonstrated.

The effectiveness of temporary flood protection is highly variable depending on the location, application, and the nature of flood events. This thesis evaluates sand-filled geotextile containers used as flood protection products within a framework of standardized tests. Specifically, Syn-Tex Wave Breakers and Super Sandbags are tested in both laboratory and field settings to quantify seepage rates, stability and durability. This allows informed decisions to be made regarding appropriate applications for each temporary flood protection product, and identifies areas for product improvement and development. The products tested performed well over the range of loading conditions applied. Large sand-filled geotextiles would be well-suited for situations where stakeholders have a low tolerance for risk, and there is adequate site access for the construction equipment required for installation. An ideal installation would be a long, relatively straight stretch where vertical product/wall and product/product interfaces can be minimized.

Zugl.: Freiberg (Sachsen), Techn. Univ., Diss., 2005

Le disjoncteur modulaire protège les installations électriques basse-tension contre les défauts de court-circuit. L’arc électrique, généré dans la chambre de coupure du disjoncteur lors de l’ouverture du circuit, est fractionné en plusieurs arcs dans un assemblage de multiples plaquettes métalliques, afin de limiter l’intensité du courant et d'isoler le défaut. Le travail exposé dans ce document se concentre sur la phase de limitation de l’intensité du courant de court-circuit. Une chambre d’arc modèle représente de façon simplifiée l’environnement de l’arc électrique durant cette phase. L'arc est amorcé par une impulsion haute-tension entre deux plaquettes métalliques fixes, l'onde de courant est transitoire et de forte intensité. La pertinence du montage expérimental est validée par la confrontation des phénomènes qu'il permet d'observer à ceux rencontrés dans le disjoncteur. Une attention particulière est portée à la tension d'arc, qui est une caractéristique déterminante pour la performance de la limitation. L’influence du matériau des électrodes est étudiée, en distinguant le substrat d’un éventuel revêtement. / The modular circuit breaker protects low-voltage lectrice installations against short-circuit faults. The electric arc generated in the arc chamber of the circuit breaker upon opening of the circuit is divided into several arcs in an assembly of multiple metallic plates, in order to limit the current and isolate the fault.The work set out in this paper focuses on the short-circuit current limitation phase. A model arc chamber represents in a simplified way the environment of the electric arc during this phase. The arc is initiated by a high-voltage pulse between two fixed metal plates, the current wave is transient and of high intensity.The relevance of the experimental setup is validated by comparison of the phenomena that it allows to observe with those encountered in the circuit breaker. Particular attention is paid to the arc voltage, which is a determining feature for the performance of the limitation. The influence of the material of the electrodes is studied, distinguishing the substrate from a possible coating.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17866号 / 工博第3775号 / 新制||工||1577(附属図書館) / 30686 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 教授 藤田 正治, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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