The most common method of monitoring and mapping groundwatercontaminants is to extract and analyse a number of groundwatersamples from wells in the investigation area. However, thereare a number of limitations with this type of point-wiseinvestigation, as it is hard to acquire an adequate picture ofa heterogeneous and anisotropic subsurface using a fewpoints. To overcome the limitations of point investigations and toimprove ground monitoring investigations in a cost-effectiveway, support can be provided by direct current resistivitymeasurements, which give a characterisation of the electricalproperties of a ground volume. The main objective with this work was to investigate theusability of the resistivity method as a support in monitoringgroundwater contaminants in glaciated terrains and underdifferent seasons, both in long-term monitoring programmes andintracer tests. The work comprised field investigations at several differentsanitary landfills and four tracer tests in differentgeological environments, around the Stockholm region. The maininvestigations have been done at Högbytorp, Stockholmwhich has been used for long-term investigations of theresistivity variation, together with a field set up formonitoring and measurements on seasonal variation in soilmoisture, ground temperature and precipitation. It can be concluded that the use of resistivity measurementssupplies valuable information in the case of mapping andmonitoring conductive groundwater contaminants andfurthermore: The variation in resistivity (in shallow investigations<1 m) can be extensive between different seasons (around30 % compared to a mean value in till and clay soils) andshould be considered, so that anthropogenic affects can beseparated from natural resistivity variation. For deeperinvestigations (>5 m) the seasonal resistivity variationwas more moderate (around 15% compared to a mean value intill and clay soils). Soil moisture variation shows a strong relationship toresistivity variation in the investigated clay and tillsoils. Together with temperature correction 47 to 65% of thevariation has been explained. Three types of monitoring systems can be applied:Permanently installed, partly installed and fully mobilesystems. For the actual measurements, all three types can useeither high-density techniques such as CVES (ContinuousVertical Electrical Sounding) or low-density measuring withone or some different electrode spacings. The suggested evaluation tool for monitoring programmesshowed that it was possible to detect a decrease of 15 % inthe mean value at a specific site using Modified Double Masscalculations between resistivity time series and time seriesat a reference site with a comparable seasonalvariation. Resistivity measurements may be used as a valuablecomplement to groundwater sampling in tracer tests. Adecrease in resistivity, a minimum and a recovery phasereflect the passage of a NaCl-solution, which can be used toestimate flow velocity and flow patterns of the investigatedaquifer. The achieved recovery of NaCl in the tracer testscarried out was estimated to 20 to 70 %. The measurement system for long-term monitoring or tracertests, which should be chosen with regard to layout andfrequency, depends on the purpose of measurement and onsite-specific conditions and therefore no standard solutioncan be proposed. Key words:Resistivity, Direct Current, Monitoring,Groundwater, Contaminant, Tracer test, Geophysics.

Emanating from the proceedings of CIGRE 2004, a new idea for higher power transmission by recycling and up rating high voltage alternating current transmission lines for high voltage direct current application was presented at the HYDC working group session. To date, there is no known application of the idea. Globally, transmission congestion, power transfer bottlenecks with restricted and limited power transfers and unobtainable servitudes challenge electric power utilities. The literature review shows that since the early sixties, several authors have studied this proposal. However, no applications were done. Admittedly, early HYDC technology was troubled by problems with multi-terminal designs, external insulation breakdown in the presence of DC stress and mercury valve rectifiers struggled with arc backs. To date, power electronic and external insulation technology has grown and matured for confident application both in point to point and multi-terminal application. The economic costs of introducing the DC technology are also more affordable given reducing prices due to higher volume of purchases. With promising developments in insulation and power electronic technology and driven by South Africa's surging growth in the consumption of electrical energy; the subject of upgrading HYAC transmission for HYDC application is revisited. For the research, the emphasis is beyond FACTS and towards a solution that could develop into a new supergrid that could overlay the existing national grid. Thus, the solution is prepared specifically for the case of recycling existing assets for higher power transfers. The working environment is defined by the difficulty in acquiring new powerline servitudes, transmission congestion in complex networks, the need for electrical islands within complex interconnections, and the need for enhanced power system stability and to promote new ancillary services energy management. The focus of this research study was to determine the technical feasibility of upgrading of existing HYAC circuits for HYDC application. It is assumed that the transmission line will remain as is in structure, layout and mechanical design. The changing of external line insulators using live line technology is an accepted modification to the original HYAC line, if required. From the study, we conclude that not all HYAC lines are recommended for upgrade to HYDe. We introduce boundary conditions as a first step towards checking on the suitability of the proposed upgrade from HVAC to HYDC mode. Emanating from this study, the first paper published introduced the initial boundary conditions as being only those lines where the "unused gap" between surge impedance loading and conductor current carrying capability is appreciable and large; generally three to four times surge impedance loading. In the case where the unused gap is the smallest or negligible, then we do nothing. In between, where the unused gap is about two to three times the surge impedance loading, then we can consider active or passive compensation using the HVAC FACTS technology options as proposed by EPRl. Having determined the candidate transmission line configuration for the proposed upgrade to HYDC application, we select the DC operating voltage as based on the voltage withstand capability of external insulation for varying environmental conditions. In addition, the DC voltage will generate allowable electrical fields and corona effects within and outside the transmission servitude. The optimum DC operating voltage would satisfy the conditions of minimum transmission power losses and volt drop for the case of maximum power transfers; within the limits of electrical fields and corona effects. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

HVDC transmission is today widely used in modem Power Systems as an alternative to HVAC. Current trends indicate that many future conventional HVDC systems will be systems of increasing power ratings, delivered over larger distances as well as multi-terminal systems. In order to ensure the security and dependability of such systems, the current protection schemes need to be evaluated to assess their ability to provide adequate protection for the envisaged HVDC systems. This research work firstly reviews the present HVDC transmission line protection systems, and highlights their advantages and disadvantages, including factors that adversely influence their performance. The author critically evaluates the current protection schemes and reveals the drawbacks and other factors that render them unsuitable for the protection oflong dc transmission lines. The author then goes on to propose and develop an HVDC line protection system that will be able to provide adequate protection for proposed long HVDC transmission lines. The proposed protection system is able to make decisions based solely on local detection increasing its overall reliability. The author then recommends that the proposed protection system be used in conjunction with the existing main protection system in order to optimise the protection response times for both close in and distant faults. The author also proposes and develops a method of further enhancing the reliability of the protection system by the use of the telecommunication infrastructure when available. Finally the performance and feasibility of the proposed protection system is evaluated using the results obtained from the extensive fault simulations performed in EMTDC and Matlab. The simulations are performed using a bipole model of an HVDC System on which the required line and protection systems are modelled. The simulation results obtained are very favourable and promote the use of this proposed protection system, for the protection of long HVDC transmission lines. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The main aim of this study was concerned with the design and commissioning of a corona cage, which could be used under Direct Current (DC) conditions. The cage was designed based on empirical formulas and equations as well as electric field simulations. The designed cage was then fabricated. The commissioning of the cage was undertaken in the High Voltage Direct Current (HVDC) laboratory at the University of Durban - Westville (UDW). Tests to determine the effects of a silicone coating as well as wind on the corona performance of conductors were undertaken. The tests were done in order to determine ways of improving the corona performance of conductors under HVDC potential. The tests were carried out using various conductor surface conditions. The wind tests were made possible by using a powerful fan. A silicone coating was also used to determine the effects that it would have in mitigation of corona activity on HVDC conductors. The conductors were tested without the coating, with half of their length coated and then fully coated. Results showed that the effect of wind on corona generation in a corona cage is minimal. The effect of the silicone coating was that it increased the corona currents measured in the corona cage. The conductors with no coating generated the lowest currents, the half coated conductors generated the second highest measured currents and the fully coated conductors generated the most corona. Analysis of the increased currents showed that the increase in corona currents due to the silicone coating could be attributed to three factors. Firstly the coating caused an increase in conductor to cage capacitance. Secondly, partial discharges could have occurred in the silicone due to microscopic air particles and lastly, the increase in corona currents could be ascribed to the effect of the boundary conditions on the boundary between the conductor and the coating. / Thesis (M.Sc.)-University of Durban-Westville, 2003.

The main aim of this project was to determine the extent to which the study of electric fields and ions in a laboratory can be used to study the electrical environment below High Voltage Direct Current (HVDC) transmission lines. The focus of the study was to set up small scale laboratory experiments and to compare these results to actual line measurements and to software simulations. The laboratory tests were undertaken at the HVDC Centre at the University of KwaZulu-Natal (Westville Campus). The software simulations that were conducted as part of this study were done using EPRI TL 3.0 and Microsoft Excel. Initially tests conducted were the measurement of the induced voltage and corona leakage current on a floating object. The next set of laboratory tests conducted was the measurement of ion current density and the electric field at ground level. The ion current density was measured with a Wilson Plate (lm2) and the electric field at ground level was measured using a JCI static monitor field meter (JCI 140) and a Monroe (257D) Portable Electrostatic Fieldmeter, with an elevated earth plane. Measurements of ion current density and electric field at ground level were also taken under an operating HVDC transmission line (Cahora Bassa to Apollo), in order to compare the laboratory measurements and simulations with real line measurements. The results have shown that the electrical parameters (i.e. ion current, induced voltages, corona currents, electric field, ion density, space charge) are higher under the negative pole as compared to the positive pole. The results of the laboratory measurements show that the ion currents under the negative polarity are almost double the ion currents that were measured under positive polarity, while the electric field under negative polarity was 20 percent higher than under positive polarity. Measurements of the electric field show that the total electric field below the line is greatly enhanced when corona generated space charge is present. The results of the EPRI TL Workstation simulations show good correlation with the EXCEL® simulations. However, there was poor correlation between EPRI simulations and test line measurements in the laboratory. The EPRI simulations show good correlation to the measured electric field values below the Cahora Bassa line. The comparison between the actual measurements on the test line and the Cahora Bassa line showed poor correlation and this was attributed to factors such as scaling, laboratory size constraints, ion concentration in laboratory, line loading and wind speeds. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

No description available.

Techn. Univ., Diss.--München, 2002.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed October 25, 2007) Includes bibliographical references (p. 61-62).

It has been estimated that 15 million individuals around the world experience the ill effects of neural disabilities every year. Neural disabilities can affect motor control, such as Locked in Syndrome or Amyotrophic Lateral Sclerosis, whereas other affect working memory, such as schizophrenia, Alzheimer's and Parkinson's. However, recent research has show that mental rehearsal of physical movement tasks may remain intact following higher centre damage, and as such represents a new opportunity to accessing the motor system and using it to control devices. Brain Computer Interfaces (BCI) captures the brain's electrical activity and translates it into real time electrical outputs, independent of the orthodox output pathways of peripheral nervous system and muscles. Utilising the brain's electrical activity BCI has the potential to significantly enhance the lives of many individuals suffering from neurological disorders. Unfortunately, the electrical activity associated with motor activity in these individuals can be lower than normal, with acute cortical infarcts decreasing the alpha wave oscillations for the affected pericentral sensorimotor areas. This has brought into doubt whether the intensity of brain signals in these individuals can be large enough to be used as a BCI system control signal for biofeedback training. This thesis aims to examine both if alternative EEG signal can be used and if externally applied neuromodulation can facilitate the process.

This research investigates the modeling and simulation, using the state transition approach to nonlinear system simulation, of a DC drive system. The drive system that was modeled is a closed loop system composed of a velocity loop with an inner current loop. The power stage is composed of a pulse generator module and a scr bridge, while the motor is a permanent magnet DC motor. A detailed development of each module model is included to reveal the open loop characteristics of the system. A total system state model was developed from each of the modules and closed loop simulations were run. The results show that the system may be modeled and simulated using this technique. However, the exactness of the simulation is heavily dependent on the DC motor parameters selected for the model. / Master of Science