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Cet article propose une critique des catégories territoriales utilisées dans les recensements brésiliens par l’Institut brésilien de géographie et statistique (IBGE). Les études de cas présentées illustrent la difficile compatibilité entre des données localisées de population et une approche géographique du peuplement. De nombreux écarts apparaissent lorsque l’on confronte des images de terrain (photographies) et satellitaires rendant compte des formes réelles d’occupation du sol aux découpages officiels distinguant les territoires urbains et ruraux. Ces décalages sont liés à plusieurs facteurs : la définition légale de l’urbain, l’agrégation des données, ainsi qu’une confusion entre population de la ville (ceux concentrés au chef-lieu du município) et population urbaine totale municipale. De tels écarts sont également la conséquence de processus historiques et d’enjeux politiques, économiques et fonciers. Ils affectent les résultats agrégés des données de recensements (population urbaine, taux d’urbanisation…), ainsi que les résultats locaux, pour chaque município. Les exemples analysés dans cet article montrent que la richesse statistique et cartographique diffusée par l’IBGE pourrait être mieux utilisée notamment pour obtenir des mesures plus cohérentes des « degrés d’urbanité » ainsi qu’une meilleure connaissance des différentes formes et densités du peuplement dans le pays. Este artigo oferece uma crítica das categorias territoriais utilizadas nos censos brasileiros pelo Instituto Brasileiro de Geografia e Estatística (IBGE). Os estudos de caso apresentados ilustram incompatibilidades entre os dados populacionais localizados e uma abordagem geográfica do povoamento. Numerosas discrepâncias aparecem quando se compara fotografias e imagens de satélite mostrando as formas reais de uso do solo, às divisões oficiais que distinguem territórios urbanos de rurais. Estas discrepâncias estão ligadas a vários fatores: a definição legal do urbano, a agregação de dados e a confusão entre a população da cidade (aquelas concentradas na sede do município) e a população urbana municipal total. Tais discrepâncias são também consequência de processos históricos e de questões políticas, econômicas e fundiárias. Elas afetam os resultados agregados dos dados do censo (população urbana, taxa de urbanização etc.), assim como os resultados locais de cada município. Os exemplos analisados neste artigo mostram que a riqueza estatística e cartográfica disponibilizada pelo IBGE poderia ser mais bem utilizada, em particular para obter números mais coerentes quanto aos « graus de urbanidade », bem como um melhor conhecimento das diferentes formas e densidades de assentamento no país. This article offers a critique of the territorial categories used in Brazilian censuses by the Brazilian Institute of Geography and Statistics, IBGE. The case studies presented illustrate the difficult compatibility between localized population data and a geographic approach to settlement. Numerous discrepancies appear when one compares field images (photographs) and satellite images that show the real forms of land use with official divisions that distinguish between urban and rural territories. These discrepancies are related to several factors: the legal definition of urban, the aggregation of data, and confusion between the city population (those concentrated in the capital of the municipality) and the total municipal urban population. Such discrepancies are also the consequence of historical processes and political, economic, and land issues. They affect the aggregate results of the census data (urban population, urbanization rate, etc.), as well as the local results for each municipality. The examples analyzed in this article show that the statistical and cartographic wealth disseminated by the IBGE could be better used, especially to obtain more coherent measures of « degrees of urbanity » and a better knowledge of the different forms and densities of settlement in the country.

This Bachelor thesis has been written at the Blekinge Institute of Technology. This thesis concentrates on the wind power and their components, also the large wind farm is studied. The electrical power is generated by using the power in wind to drive a wind turbine to produce mechanical power. This mechanical power can be converted into electrical power by using electrical induction generators. There are two types of the wind turbines, the horizontal axis and vertical axis wind turbine, where the horizontal axis wind turbine is mostly used and was studied in this thesis. The rotor can be placed in two directions: an upwind rotor where the blade of turbine faces to the wind, so it operates more smoothly and transmit more power. The other type is a downwind rotor which orients itself with respect for the wind direction. Moreover, the tower shadow makes the blade to flex, consequently resulting in fatigue, noise, and reduces output of the power. The modern wind turbine has been built with an odd number of blades which is important for the stability of the turbine. The rotor with an odd number of blades can be considered to be similar to a disc when calculating the dynamic properties of the machine. The main idea of this thesis is to study the wind power in general and large wind parks specifically. The Horns Rev wind park was taken as an example of a wind park in Denmark and the Gotland wind park as an example of a wind park in Sweden too. Into account, the distance between wind turbine in the wind direction cannot be too small. If the wind turbines are located to close to each other, the wind will be more and more turbulent after it passes through each single wind turbine. This would lead to that wind turbines downstream in the wind park, and it might even have to shut down due to that mechanical loading gets to high during strong conditions. This is due to the fact that when wind passes through the rotor of the wind turbine it gets very turbulent and the wind speed is decreased. The minimum length of the rotor should be approximately 5-7 rotor diameters to avoid that issue. Gotland Energy AB (GEAB) considered, that high voltage direct current light would be the only realistic way to solve the technical problems for the high amount of wind power in-feed. One result is that The stability of voltage during transient events, has become much better by using the high voltage direct current light so that the output current stability from the asynchronous generators have been improved, which reduces the stresses on the AC grid and on the mechanical construction of the windmills. In general the wind turbines with three blades accommodated a thicker root are used. It is obvious that, the less number of blades on the wind turbine, the cost of material and manufacturing will be lower. It is worthy to mentioned that, the modern wind turbine has been built with an odd number of blades. When the length of the blade increases the deflection of blade tip due to axial wind force also increase as well. So without consider the increase in length of blade may lead to dangerous situation of collision of tower and blade. Moreover, by increasing the number of blades cost of the system would increased as well. The limit of transfer for the AC transmission system depends on the distance from shore and is therefore physically limited by this. AC large wind parks that are placed at a long distance from the shore, which means AC long transmission line, and more drop voltage A solution to AC long transmission line, it could be to decrease the offshore frequency and use a low frequency AC networks. There is a suggestion by for instance (Schütte, Gustavsson and Ström 2011). The usages of a low frequency system are in electrified railway systems, where the frequency ranges from 16.67 Hz to 25 Hz. However, the network of a low frequency would allow a simpler design of the offshore WTs and The aerodynamic rotor of a large WT operates at maximum revolutions at 15-20 rpm. The lower frequency would then allow a smaller gear ratio for turbines with a gearbox, or decrease the poles number for WTs with direct driven generators. This would lead to lighter and cheaper turbines. One of the disadvantages by using a low frequency system is the size of transformer would be increased, and hence, the costs of transformer will increased too. The operator of the grid, Gotland Energy AB (GEAB) considered, that HVDC light would be the only realistic way to solve the technical problems for the high amount of wind power in-feed. The experiences have supported expected improvements in the characteristics for example: - Stability in the system arose. - Reactive demands, power flows, as well as voltage level in the harmonic and system were reduced. - Flicker problems were eliminated with the installation of HVDC light and transient phenomena disappeared. Moreover, Overall experiences of Gotland Energy AB (GEAB) are that the control of power flow from the converters makes the AC grid easier to observe than a conventional AC network and the power variations do not stress the AC grid as much as in normal network. Voltage quality has been better with the increased wind power production. A topic to study in the future is the consequences of blackouts in power supply with many wind power farm. 004676396018