In this thesis we determine the electromagnetic fields of a current distribution located, in free space, above a perfectly conducting plane earth. Then we consider the inverse problem of determining the source distribution from the fields. Formulae are obtained for the volume integral (dipole moment) of the current density of a small current source in terms of the fields and known functions. If field data are measured (from lightning over sea water for example) the dipole moment of the current density producing the fields may be found. The validity of the small source approximation used in this work is also established. Finally, a method is developed for determining the average current at points on a vertical line current source, a common model for a lightning return stroke. We treat the source as a string of dipoles and apply a method of constrained inversion.

In general, tailings dams are expected to seep. Anomalous seepage, especially when induced by internal erosion, is a major concern for owners and operators. The long established techniques for monitoring water seepage provide sparse information which may not be sufficient to detect and map the seepage path. Hence, there exists a great need for non-invasive techniques that would be sensitive to changing seepage conditions. The non-invasive nature of the techniques is particularly important because drilling and other penetrating (invasive) investigation methods are normally avoided. / Non-invasive techniques such as self-potential and high-resolution resistivity have been significantly improved in the past decade and have been successfully used for water retention dam investigation and monitoring. The main difficulty in the use of these techniques in monitoring sulfide rich tailings dams is the presence of electrochemical potentials that renders the interpretation of the acquired self-potential data difficult. / Numerical modelling is one of the latest methods in interpreting self-potential anomalies induced by liquid flow. But, in order to model streaming potentials several parameters need to be measured or estimated; (1) the hydraulic driving force and the hydraulic conductivity are required to solve for the hydraulic pressure distribution; (2) the cross-coupling conductivity distribution is needed to calculate the conduction current source parameter; and (3) the resistivity distribution is needed to determine the resulting potential distribution. / The zeta-potential and the resistivity of three pyrite rich tailings from the Abitibi region in Quebec were measured over the pH range 2 to 5 in different KCl aqueous solutions for the purpose of estimating the magnitude of electrokinetic effect induced by mine water seepage and the electrical resistivity variation induced by particle migration. The experimental and theoretical results obtained in the present study are pertinent to the interpretation of self-potential data. The zeta-potential was found to vary from -27 to -2 mV and the resistivity of the tailings was found to increase when fine particles are eroded.

No description available.

A method of measuring the negative-sequence current in an unbalanced three-phase circuit. A four-winding current transformer, in conjunction with a phase shift network and an alternating current ammeter, was used for obtaining a current proportional to, and in phase with, the negative-sequence current. After calibration, readings were taken of the three line currents in a three-phase three-wire circuit and of the current in the negative-sequence ammeter. The negative-sequence current. was calculated from the line currents and compared with the ammeter reading. The difference between the two values, in most cases, was less than five per cent of the ammeter reading. It was found that. the circuit had to be calibrated for each type of ammeter used. It was concluded that direct readings of negative-sequence currents can be made with accuracy consistent with commercial requirements. / Master of Science

A one-dimensional analytical model of dark current has been developed to facilitate the investigation and analysis of dark current from gate-controlled photovoltaic InSb arrays. The applied gate voltage is an essential parameter in the model. The expressions relating this parameter to surface potential are derived separately for the cases of accumulation and depletion at the surface of n-type InSb material under the gate. In addition, the measured dark current is compared with that from the analytical model, and the discrepancy is discussed in terms of the intrinsic carrier concentration, surface recombination velocity, and geometry of the array. The components of dark current are mainly associated with surface state generation-recombination, field induced tunneling, and the depletion region from the bulk and surface. The experimental results are obtained at temperatures between 30K and 40K.

CAPES / Uma má qualidade de energia elétrica gera grandes prejuízos para a sociedade. Desta forma são utilizados equipamentos denominados analisadores de qualidade de energia elétrica para quantizar os valores destes distúrbios e assim determinar as causas destas anormalidades. O grande problema destes equipamentos é o custo elevado e geralmente são importados inviabilizando uma medição multiponto do sistema elétrico do cliente. Neste cenário, este trabalho objetiva fornecer subsídios e alternativas para o desenvolvimento de equipamentos analisadores de qualidade de energia, que consiste de um conjunto com sensores de corrente e tensão e um módulo central de processamento. No desenvolvimento de quaisquer sensores ou instrumentação surgem algumas dificuldades de condicionamento de sinal por causa das características elétricas do componente usado e principalmente por causa do ruído. Alguns meios de contornar estes problemas são a utilização de uma instalação adequada dos equipamentos de medição, blindagens eletromagnéticas e projeto de PCB’s. No caso de sensores magnéticos, a histerese, saturação magnética e as interferências por campos magnéticos externos introduzem erro de medida no sistema e para a resolução destes problemas foram adotadas configurações de sensores Hall em malha fechada e diferencial. Outro componente que pode ser usado é o sensor Flux-gate que possui potencialidade para medições de corrente de pequena ordem além de oferecer a vantagem de maior integrabilidade ao sistema medidor. Na sequência foi projetado e construído um registrador de tensão e corrente para análise de qualidade de energia elétrica, denominado PQ-Logger, que pode usar estes sensores mencionados anteriormente. O uso de um DSP e um chip para acessar um pendrive genérico permite o armazenamento destes dados. O PQ-Logger-Tran é outro equipamento que foi idealizado para armazenar trechos de transiente de média frequência. Os resultados indicam positivamente o uso conjunto destes sensores de corrente e o equipamento desenvolvido para o propósito de medição destes parâmetros de forma rápida e econômica na infraestrutura elétrica do cliente. / A poor quality power causes large losses to society. Thus it is used an equipment named power quality analyzers for magnitude measurement of these disturbances and determine the causes of these abnormality. The principal problem with these devices is the high cost and they usually are imported that invalidates multipoint measurement of client’s electrical system. In this scenario, this work aims to provide support and alternatives for the development of power quality analyzers, which consists of a set with voltage and current sensors and a central processing module. In the development of any sensors or instrumentation there are difficulties on signal conditioning generated from the used component’s electrical characteristics and principally noise. Some solutions for these problems is the use of proper measuring equipment installation, electromagnetic shielding and design of PCBs. For magnetic sensors, the hysteresis, magnetic saturation and interference by external magnetic fields introduce measurement error in the system and to solve these problems it was adopted Hall sensors in closed-loop and differential configurations. Another component that can be used is the Flux-gate sensor that has potential use in small range current measurements and offers the advantage of higher integrability in the meter system. Following is designed and built a voltage and current logger for Power quality analysis, called PQ-Logger that may utilize the sensors mentioned above. The use of a DSP and a chip for accessing a generic flash drive allows storage of these data. The PQ-Logger-Tran is other equipment that was designed to store snippets of mid-frequency transient. The results positively indicate the combined use of these current sensors and equipment developed for the measuring purpose of these parameters in a quickly and economically form in the customer‘s electrical infrastructure.