The sun is constantly emitting electrons and ions as magnetized plasma, forming the solar wind and carrying with it the sun’s rotating magnetic field. The solar wind subsequently interacts with Earth’s magnetosphere and the magnetospheres of other planets. Occasionally large amounts of magnetized plasma are released at one time in a Corona mass ejection (CME). When the CME interacts with Earth’s magnetic field, it induces perturbations that may have a significant impact on critical infrastructure, for instance, by disturbing communication systems, and inducing currents on pipelines and electric power lines, which in turn may cause increased corrosion or blackouts, among other effects. In this dissertation, we analyze measured electrical signals provided to us by the Finnish Meteorological Institute, which were induced by geomagnetic storms on pipelines located in Finland and recorded in 2003. Specifically, we perform a wavelet leader multifractal analysis of these current signals to generate singularity spectra, and then using the bootstrapping technique, we apply statistical tests to show that these signals exhibit multifractal characteristics. We also performed surrogate testing to show that these characteristics were unique to the signal. / Ph.D. / Earth’s weather affects all of us every day. The solar space environment has weather of its own that affects us as well. Storms of a size that far exceed anything on Earth can impact Earth and affect our infrastructure. One of the most powerful phenomena that occur, called solar corona mass ejections, results when the sun ejects a large amount of plasma. This can interact with the Earth’s magnetic field, which in turn induces perturbations that may have a significant impact on critical infrastructure, for instance, by disturbing communication systems, and inducing currents on pipelines and electric power lines. The currents can cause increased corrosion or blackouts, among other effects. In this dissertation, we analyze measured electrical signals provided to us by the Finnish Meteorological Institute, which were induced by geomagnetic storms on pipelines located in Finland and recorded in 2003. Specifically, we perform a statistical analysis of these current signals to decide whether they exhibit multifractal characteristics.

This thesis investigates geo-electric fields in the United Kingdom with particular regard to Geomagnetically Induced Currents (GIC) in the Scottish Power electricity transmission network (SPTN). The joint spectral characteristics of Scottish Power GIC and Eskdalemuir magnetic observatory data are analysed, and GIC are shown to be coherent with magnetic field variations over the period range 2-1100s. A bi-variate transfer function model of the physical link between magnetic field variations and GIC demonstrates that long-period (>200s) induction makes a first order contribution to the observed GIC at one SPTN site, and dominates the response at another. Thin-sheet modelling at a period of 750s is used to explore the relative influence of three factors on the size and spatial distribution of the calculated electric field: (i) the contrast in conductance between the sea and the land; (ii) variations in conductance due to sea depth; (iii) lateral variations in conductance representative of those in the geographic area occupied by the SPTN. The modelling suggests that a `coast-only' model (i) will over-predict electric field magnitudes in the SPTN region by a factor of 2-5 in comparison with model (iii). Distortion analysis of Magnetotelluric (MT) data at a period of 750s acquired over numerous field campaigns reveal pervasive galvanic distortion of the electric field in the SPTN region. GIC transfer functions of one site are consistently interpreted as proxy MT responses, and it is shown that galvanic distortion of the electric field modifies significantly the GIC amplitude response. A prototype model of the SPTN developed by the British Geological Survey and the Finnish Meteorological Institute is used to calculate GIC. It is shown that neglect of lateral variations of conductivity may lead to false conclusions about the direction of the external electric field that maximises GIC. Time derivatives of the Eskdalemuir horizontal magnetic field are used as an index of GIC activity, and to select events which may have led to large GIC in the time period (1983-2000) prior to the monitoring of GIC by Scottish Power. Backwards-prediction using the GIC transfer functions and observatory magnetic data suggests that GIC at the Scottish Power monitoring sites have amplitudes less than approximately 30A.

This thesis documents the work undertaken to investigate and improve the theoretical and practical requirements for two-dimensional hydrodynamic modelling of coastal and estuarine areas, in particular to the inter-related aspects of: - wetting and drying of relatively large intertidal areas, and - the influences of waves on both current generation and variations in mean water level. The work outlined in this thesis began as a result of a perceived lack of understanding and confidence in the application of finite element models to coastal and estuarine situations. In response to this observation an investigation into the modelling parameters, particularly those that affect model performance during the simulation of wetting and drying, was undertaken. This initial investigation into the effect of these parameters upon model performance forms the first component of this study. Testing was performed to provide a quantitative assessment of the effect of these parameters upon model performance. The initial tests were simple examples designed to investigate the behaviour of a single specific parameter. Subsequent tests were more complex and assessed the combinations of various parameter selections. Once the model was shown to accurately simulate the movement of waters in a coastal and estuarine environment, wave forces were incorporated. The aim of the second component of the study was to modify the hydrodynamic model to predict the net current and water levels attributable to the influences of waves. Tests examined the effects of the application of wave induced forces in a range of applications, including the simple case of a uniform beach, comparisons to a physical model, and an example from a real coastline. The final outcome of this study is the development of a modelling tool that can accurately represent the forces of tides, winds and waves upon water movement in a shallow coastal and/or estuarine region. Furthermore, the qualitative and quantitative assessments of parameters that affect the performance of the model provide greater confidence in model results and better understanding of the applicability and limits of the modelling technique. Principal outcomes of the study are: - an improved understanding of the parameters which influence the behaviour of hydrodynamic models; - a better understanding of the applicability and limits of the modelling technique; and - an enhanced software system based on an existing modelling software system which is applicable to studies that require simulation of the combined forces of tides, winds and waves.

Power transformers are a key element in the transmission and distribution of electrical energy and as such need to be highly reliable and efficient. In power system networks, transformer core saturation can cause system voltage disturbances or transformer damage or accelerate insulation ageing. Low frequency switching transients such as ferroresonance and inrush currents, and increasingly what is now known as geomagnetic induce currents (GIC), are the most common phenomena to cause transformer core saturation. This thesis describes extensive simulation studies carried out on GIC and switching ferroresonant transient phenomena. Two types of transformer model were developed to study core saturation problems; one is the mathematical transformer magnetic circuit model, and the other the ATPDraw transformer model. Using the mathematical transformer magnetic circuit model, the influence of the transformer core structure on the magnetising current has been successfully identified and so have the transformers' responses to GIC events. By using the ATPDraw transformer model, the AC system network behaviours under the influence of the DC bias caused by GIC events have been successfully analysed using various simulation case studies. The effects of the winding connection, the core structure, and the network parameters including system impedances and transformer loading conditions on the magnetising currents of the transformers are summarised. Transient interaction among transformers and other system components during energisation and de-energisation operations are becoming increasingly important. One case study on switching ferroresonant transients was modelled using the available transformer test report data and the design data of the main components of the distribution network. The results were closely matched with field test results, which verified the simulation methodology. The simulation results helped establish the fundamental understanding of GIC and ferroresonance events in the power networks; among all the influential parameters identified, transformer core structure is the most important one. In summary, the five-limb core is easier to saturate than the three-limb transformer under the same GIC events; the smaller the side yoke area of the five-limb core, the easier it will be to saturate. More importantly, under GIC events a transformer core could become saturated irrespective of the loading condition of the transformer.

To facilitate the process of setting up small scale environmental models in coastal and offshore areas a wave model and a 2D current model for the Baltic Sea have been set up with MIKE 21. The ambition is that the Baltic Sea model can serve as a source of boundary conditions for local models. The main focus in the project has been to determine which input data to use to get the best results and then to calibrate and validate the model with the best data sets available. The wave model has been tested with three different sources of wind forcing and the results with the different sources are evaluated. The wave model has been calibrated and validated against five wave buoys and the current model against three current observation stations. The comparison shows that the wave model gives good estimations of wave height, period and direction. The output of the current model coincides with observations where distinct current patterns exist. The wave model is considered a good source to extract wave statistics from for the entire Baltic Sea. The current model can be used for scenarios or areas that do not suffer from the limitations of a 2D model.

No description available.

Submitted by Marlucy Farias Medeiros (marlucy.farias@unipampa.edu.br) on 2017-10-31T16:57:28Z No. of bitstreams: 1 Fabiana_da Cunha Lagoas - 2017.PDF: 14321561 bytes, checksum: 3289d01da05021ff92313e5754afb5f8 (MD5) / Approved for entry into archive by Marlucy Farias Medeiros (marlucy.farias@unipampa.edu.br) on 2017-10-31T18:24:31Z (GMT) No. of bitstreams: 1 Fabiana_da Cunha Lagoas - 2017.PDF: 14321561 bytes, checksum: 3289d01da05021ff92313e5754afb5f8 (MD5) / Made available in DSpace on 2017-10-31T18:24:32Z (GMT). No. of bitstreams: 1 Fabiana_da Cunha Lagoas - 2017.PDF: 14321561 bytes, checksum: 3289d01da05021ff92313e5754afb5f8 (MD5) Previous issue date: 2017-09-28 / Correntes geomagneticamente induzidas (GICs) são correntes espelhadas na superfície terrestre, que ocorrem em função do movimento de partículas ionizadas no campo magnético terrestre. Tais partículas eletricamente carregadas são provenientes da massa coronal expelida em erupções solares, as quais viajam a uma velocidade de, aproximadamente, 450 km/s. Ao entrarem em contato com a magnetosfera, proporcionam distorções no campo magnético, as quais são medidas por meio de três índices geomagneticos: Kp e Ap, que representam o grau de perturbação do campo magnético, e Dst, o qual informa a intensidade da tempestade solar por hora. Quando as GICs penetram no sistema elétrico de potencia (SEP) através dos aterramentos dos equipamentos, problemas podem ocorrer, tais como o aquecimento de componentes da rede, além de desligamentos de linhas de transmissão, decorrentes da atuação indevida de dispositivos de proteção. Destaca-se que, atualmente, as concessionarias brasileiras de energia são severamente multadas pelos órgãos reguladores quando ha a ocorrência de um desligamento não programado que não seja causado por uma falta permanente. Al˜ em disso, ressalta-se que os dispositivos de proteção são desprovidos de funções capazes de detectar as GICs, as quais comprometem também a vida útil de alguns equipamentos. Nesse contexto, um estudo aprofundando deste fenômeno geomagnético e apresentado neste trabalho. Para tal, um histórico de desarmes da Linha de Transmissão (LT) de 138 kV ALE SE – SMA1, localizada entre as cidades de Alegrete e Santa Maria, no estado do Rio Grande do Sul, foi analisado em função dos dados dos índices geomagnéticos para o período de 2010 a 2015. Além disso uma analise do ciclo solar, evidenciou a possibilidade de ocorrência de GICs nesta LT, o que pode justificar muitos dos desligamentos indeterminados. Dessa forma, o presente trabalho apresenta uma técnica para detecção de GICs, a qual pode ser aplicada em reles digitais ou em ferramentas computacionais para determinação das causas de desligamentos indevidos sem justificativa aparente. Tal método consiste em um filtro morfológico para detecção dessas correntes, o qual foi implementado em Matlab e testado a partir do processamento de sinais de corrente, gerados computacionalmente pela simulação de um sistema teste no software EMTP-ATP. Os valores de GICs utilizados para testar o seu desempenho foram obtidos a partir do software OPENDSS, o qual calcula o fluxo de corrente geomagneticamente induzida a partir de dados técnicos da LT, como o comprimento da linha e as respectivas latitudes e longitudes de seus terminais. Os resultados obtidos através das simulações em OPENDSS mostraram a ocorrência de GICs na linha estudada. Por fim, o processamento dos sinais conseguidos através da simulação do sistema, por parte da metodologia para detecção de GICs, comprovaram a excelência da técnica proposta. / Geomagnetically induced currents (GICs) are mirrored currents on the Earth’s surface, which occur as a function of the movement of ionized particles in the Earth’s magnetic field. Such electrically charged particles are derived from the coronal mass expelled in solar flares, which travel at a speed of approximately 450 km / s. When they come into contact with the magnetosphere, they provide distortions in the magnetic field, which are measured by means of three geomagnetic indices: Kp and Ap, which represent the degree of perturbation of the magnetic field, and Dst, which informs the intensity of the solar storm per hour. When GICs penetrate the electrical power system (SEP) through the grounding of the equipment, problems can occur, such as the heating of network components, as well as disconnections of transmission lines, due to the improper performance of protection devices. It should be noted that, currently, Brazilian energy concessionaires are severely fined by regulatory agencies when there is an unplanned shutdown that is not caused by a permanent shortage. In addition, it is emphasized that the protection devices are devoid of functions capable of detecting the GICs, which also compromise the useful life of some equipment. In this context, an in-depth study of this geomagnetic phenomenon is presented in this paper. To do so, a history of disarranges of the 138 kV ALE SE - SMA1 transmission line, located between the cities of Alegrete and Santa Maria, in the state of Rio Grande do Sul, was analyzed according to geomagnetic index data for The period from 2010 to 2015. And together with a study of sunspots, the possibility of occurrence of GICs in this LT was evidenced, which may justify many of the indeterminate disconnections. Thus, the present work presents a technique to detect GICs, which can be applied in digital relays or in computational tools to determine the causes of undue disconnections without apparent justification. This method consists of a morphological filter for the detection of these currents, which was implemented in Matlab R and tested from the current signal processing generated by the simulation of a test system in the EMTP-ATP R software. The values of GICs used to test their performance were obtained from OPENDSS R software, which calculates geomagnetically induced current flow from technical data of the LT, such as the length of the line and the respective latitudes and longitudes of its terminals. The results obtained through the simulations in OPENDSS showed the occurrence of GICs in the studied line. The results obtained from the processing of the signals obtained through the simulation of the system proved the excellence of the proposed technique.

Geomagnetically induced currents (GIC) are manifestations of space weather phenomena on the electric power grid. Although not a new phenomenon, they assume great importance in wake of the present, ever expanding power grids. This thesis discusses the cause of GICs, methodology of modeling them into the power system and the ramifications of their presence in the bulk power system. GIC is treated at a micro level considering its effects on the power system assets like Transformers and also at a macro level with respect to issues like Voltage instability. In illustration, several simulations are made on a transformer & the standard IEEE 14 bus system to reproduce the effect of a geomagnetic storm on a power grid. Various software tools like PowerWorld Simulator, SimPower Systems have been utilized in performing these simulations. Contingency analysis involving the weakest elements in the system has been performed to evaluate the impact of their loss on the system. Test results are laid out and discussed in detail to convey the consequences of a geomagnetic phenomenon on the power grid in a holistic manner.

Satellites have become absolute necessity in the growing modern space technology. At present, launch pads are the only means for launching of satellites or any other space vehicles. Due to the large magnitude of current and the associated rate of rise, a lightning strike to launch pads can be quite disastrous. Satellite launch complex forms typically the tallest object in that region. This makes them the more vulnerable to cloud-to-ground lightning. In addition, most of the launch pads are situated near the coastal area, where the isokeraunic levels are quite high. In view of these, almost all the satellite launch pads are provided with suitable Lightning Protection Systems (LPS). The LPS is basically intended for protecting against a direct lightning hit. The present work is related with the LPS to Indian satellite launch pads, Pad-I and Pad-II. The protection system for Pad-I consists of three 120 m tall towers placed approximately at the vertices of an equilateral triangle of 180 m. The same for Pad-II consist of 120 m tall towers placed at vertices of rectangle of size 90 m x 105 m. Towers are interconnected by 6 shield wires at the top. A mast of 10m length forms the top of the tower. Significant work on the analysis of interception efficacy of these protection systems has been reported in the literature. The lightning surge response of these systems have also been analysed and reported. The interception efficacy of these LPS in field can be ascertained by pertinent measurements. Measuring the lightning current on LPS seems to be one of the most suitable choices for this purpose. It would also greatly facilitate collection of local lightning current statistics, data on which is almost absent. Several considerations suggest that the tower bases form ideal place for such measurement. However, such lightning current records would involve mainly the current resulting from stroke interception, as well as, induced current due to strokes nearby. Literature on categorisation of measured currents to the type of stroke and correlation of measured currents to the incident stroke currents is rather limited. This is especially true for interconnected protection system of the type dealt in the present work. Considering these the present work is taken up and its scope is defined as: (i) Evolve a suitable model for study of current distribution in LPS due to Lightning and using the same deduce the current due to stroke interception and that due to stroke nearby. (ii) For the purpose of categorization identify the salient characteristics of current due to the intercepted strokes and that due to bypass/nearby strokes (iii) For the intercepted strokes, develop a processor for estimating the injected stroke current from the measured tower base currents. Lightning event, apart from other associated physical phenomena, is strongly governed by electromagnetic fields. Any method employed for the analysis, either theoretical or experimental, should satisfy the governing electromagnetic equations. As experimentation on actual system, as well as, their laboratory simulation is nearly impossible, theoretical modelling approach is selected. Modelling involves modelling of the channel along with its excitation, modelling of the LPS and modelling of the ground. Channel, following the literature, is represented as a loaded conductor with a lumped current source at the junction point. Such models have quite successfully predicted the electromagnetic fields and current in other places on the down conductor. For the LPS, some simplifications on the geometry are very essential. Tower lattice elements of dimensions much smaller than the wavelength of highest dominant frequency component of lightning current spectrum are neglected. Suitable modification is made for the tower top involving a plate and interconnection of several short members. For the close range within 200 – 400 m, even for the induced currents, the influence of ground in the literature has been reported to be small. Also, there is an extensive grounding network in these systems. In view of the same, a perfectly conducting ground along with suitable ground termination impedance is considered. Only the numerical solution of the problem is feasible and for the same, following the literature, NEC-2 is employed. All the guidelines of NEC are respected in the discretisation. Geometric mean radius is employed for modelling the complex tower elements. Fourier Transform Techniques are employed for time domain conversion of the computed frequency domain quantities. Occasionally, numerical inversion error of magnitude less than 5% is encountered. For the validation of the numerical modelling for both direct stroke and that nearby, time domain experimentation on electromagnetically reduced scale models (35:1) is employed. As the channel electrical and geometrical parameters are stochastic in nature, it is necessary to ensure that the deduction made using the model is practically relevant. For this, some parametric studies are conducted. The influence of channel length and inclination, stroke current velocity etc. has been shown to be insignificant for the case of intercepted strokes. Simulations are carried out for the stroke intercepted (i.e. direct strikes) by the LPS. The characteristics of the tower base currents are investigated. The base currents indicate a dispersive propagation along the towers and further a frequency dependent current division at the tower-shield wire junctions. Base currents contain superimposed oscillations, which basically originate from various junctions of the system. The magnitude of the oscillations is obviously dependent on the rise time of the incident currents. The tower base currents settle within about 10 -15 µs, which is shorter than that for isolated tower. Further, the full-frequency model could be limited to this time period. The corresponding current transfer functions are deduced. For the stroke interception by shield wires, based on the earlier work, only stroke to midspan is found to be relevant and hence it is considered. The nature of tower base currents for a stroke to midspan of the shield wires seem to be similar. However there are some distinct features, which are helpful in identifying the stroke location on the LPS. From the time correlated tower base currents, a suitable methodology for identifying the stroke interception location on LPS is developed. Next, simulations for induced current due to a bypass stroke, as well as, stroke to ground outside the LPS, however, within 1 km radius are taken up. In fact, it is estimated that latter is nearly 5 – 13 times higher than the strokes collected by LPS, indicating it as the most probable event. The objective here is characterization, rather than correlation. In this study, the influence of charge induced on the LPS by the descending leader is neglected and the upward leader activity is approximately considered. To the best of author’s knowledge, studies on such induced currents in down conductors are very scarce. Considering this and noting that the number of parameters is quite large, first the basic study is taken up on simple cylindrical down conductors. Many important and interesting deductions are made. The nature of the induced current is highly dependent on the rate of rise as well as the velocity of propagation of the stroke current. The magnitude and to some extent, the wave shape of the induced current is found to depend on the average as well as maximum di/dt of the stroke current. For a given wave shape, the magnitude of the induced current increases with rate of rise of the wave front; however, saturating trend will onset after some point. The height of the down conductor mainly governs the frequency of the oscillatory component of the induced current. The dependency of the induced current on the radius of the down conductor seems to be logarithmic (which is in accordance with the antenna theory). Based on these results, the parameters for the corresponding study on LPS under consideration, is chosen. The results of the investigation on the induced currents in LPS show that they have quite distinct waveform. They are basically bipolar and oscillatory in nature, with relatively short duration. These unique features facilitate clear distinction of the induced currents from that due to stroke interception. Basic characteristics are reasonably insensitive to the separation distance of the protection system and the channel, current propagation velocity along the channel, channel inclination and shape of the current front. The salient features of the induced current due to a bypass stroke are also enumerated. • The noise, if any, in the measured current can be addressed only after acquiring sufficient data. Based on the above, the following procedure is suggested for the stroke classification and estimation. • By employing the distinct features of the resulting tower base currents, analyze the measured tower base currents and classify the strokes into the intercepted stroke or stroke to ground. • For the latter case, using the salient features of the bypass strokes, further classify the strokes to bypass strokes and stroke to ground outside the protected volume. • For the intercepted strokes, using the relative strengths and wave shapes, identify the interception point to either tower top or the midspan of the shield wires. • Then by using the corresponding transfer functions and Fourier Transform techniques, compute the injected stroke current. • Using the above, other tower base currents are computed and compared with the measured currents. This gives quantification for the accuracy of the method. In summary the present work has made some original contribution to the classification and estimation of stroke currents measured on the interconnected LPS.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-11T13:09:04Z No. of bitstreams: 1 arquivototal.pdf: 1583885 bytes, checksum: 1b7650a627b47ca275b6bc5af085bd27 (MD5) / Made available in DSpace on 2017-09-11T13:09:04Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1583885 bytes, checksum: 1b7650a627b47ca275b6bc5af085bd27 (MD5) Previous issue date: 2017-02-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis, we investigate the e ect of the topology and the magnetic eld on the vacuum uctuations associated to bosonic and fermionic charged elds. Firstly, we analize the vacuum induced current densities for a bosonic eld in a (D+1)-dimensional cosmic string spacetime. For this analysis, we consider the presence of a magnetic eld along of the azimuthal and axial directions and that the z-axis is compacti ed to a circle of lenght L. This analysis is performed using the positive frequencies Wightman function, that is necessary to calculate the vacuum expectation values of the induced current densities. Our second investigation is related with fermionic elds. We investigate the expectation values of the fermionic condensate, h i, charge and current densities for a massive fermionic eld in thermal equilibrium with T temperature, with a nonzero chemical potential, . We consider the background of a (2+1)-dimensional conical spacetime and the presence of a magnetic eld in the cone apex. In this analysis, we consider two separeted cases. Firstly, we consider the case where j j 6 m and after that the case where j j > m. / Nesta tese, investigamos o efeito da topologia e de um campo magnético nas flu­tuações do vácuo associadas a campos bosônicos e fermiônicos carregados. Primeiramente, analisamos as densidades de correntes induzidas no vácuo para um campo bosônico em um espaço-tempo de uma corda cósmica com (D+1) dimensões. Para esta analise, consideramos a presença de um fluxo magnético ao longo das direções axial e azimutal e que o eixo z é com­pactificado em um circulo de comprimento L. Esta analise é realizada fazendo use da função de Wightman de frequências positivas, que é necessária para calcular os valores esperados no vácuo das densidades de correntes induzidas. Nossa segunda investigação é relacionada a campos fermiônicos. Investigamos os valores esperados do condensado fermiônico, (N), carga e densidades de corrente para u campo fermiônico massivo em equilíbrio térmico a uma temperatura T, e com um potencial químico não-nulo, µ. Consideramos um espaço-­tempo cônico em (2+1) dimensões na presença de um campo magnético no vértice do cone. Para esta analise, dois casos foram considerados separadamente. Primeiramente, considera­mos o caso em que |µ| < m, e ern seguida, o caso ern que 1p,1 > m.