As the historical development shows, both AC and DC transmission voltages have steadily increased. The growing demand for power supply induced the building of large power plants located far away from load centres. Also future projects in Europe such as DESERTEC or large offshore Wind Power Systems demand a smart solution of transmitting electric bulk power in an economic and efficient way over long distances. In order to reach this goal, very high voltages for transmission are necessary. AC-Voltages ≥ 1000 kV und DC-Voltages ≥ ± 800 kV are defined as UltraHigh-Voltages (UHV). Based on the assumption of a continuous growth of energy demand, experts considered the invention of UHV transmission level in North America and Europe already 40 years ago [1]. However -it took almost 4 decades till the first UHV AC line reached operational status in China. This paper demonstrates possible ways of transmitting large bulk power generated in offshore wind parks over a distance of roughly 600 km (about 380 miles) across Germany. It contains and discusses the results of the investigation for all relevant characteristics, fragmented into general, mechanical, electrical and ecological parameters. After a detailed look on the mechanical construction of UHV overhead transmission lines it could be stated, that this was one of the limiting factors. Also the maximum power, which could be injected into one grid point is a critical value and has influenced the reliability analyses. I. INTRODUCTIONIn 2005 the European Union passed a major Energy bill with the specific and ambitious aim to reduce the greenhouse gases by 20 %, to increase the energy efficiency by 20 %, to increase the renewable energy production contingent up to 20 % and to increase the bio-fuel percentage up to 10 %. All this should be reached by the year of 2020 [2]. In order to reach the 20 % of renewable energy generation, large offshore wind parks are under construction and partly already in operation, especially in Denmark, Great Britain and Germany. Since Germany already has a large amount of onshore wind power installed (about 22,2 GW by the end of 2007), the offshore potential is still enormous [3]. Offshore wind parks do have many advantages compared to the onshore ones. The high and constant wind speeds offshore lead to a way more
High voltage rotating machines are supposed to be optimized not only in terms of performance but -among othersalso with respect to space and material utilization. When designing machines there has been considerable effort made to reduce the overall size of generators particularly in the axial direction. The winding is one of the more demanding parts of the generator but the end winding is an obvious place where axial space could be saved. For an optimized design, the distance between adjacent insulated bars or coils is a very important factor. Inadequate end winding spacing can lead to corona activity between adjacent coils or bars. Exact prediction of the needed space is difficult as prediction is dependent upon several contributing factors. Dielectric properties of the insulation material, location of the bracing system, imperfection of insulation surface as well as of the corona inception and extinction voltage in the air gap between insulated electrodes are important factors to understand for an optimized end winding design.In this paper the results of experimental investigations on air for various electrode configurations are presented. Metallic electrodes were covered with standard insulation material which is used in generators.The corona inception and extinction voltages as well as the partial discharge rate and the amplitude were measured for different electrode configurations. Additionally, the corona discharges were monitored with a special UV camera. The distance and the pressure of the air were varied in a wide range.The main purpose of this study was to optimize and simplify the spacing requirements of the end winding design. Therefore the corona inception and extinction voltage in the air gap between insulated electrodes as a function of distance and pressure was measured. Subsequent to that, the translation between the classical Paschen's Law for breakdown and the corona inception and extinction voltage in the air gap between insulated electrodes was investigated.
Gas insulated systems, have proven to be reliable for many years. But despite of a high availability some defects, in particular free moving particles can be very critical. Contamination with particles can result from mechanical abrasion or due to vibrations as well as the enclosures damages during the assembly. A further aspect is that power transmission with DC is getting more important. Therefore Gas Insulated Systems operated with DC will be required in the future. But particle behavior under DC-condition is much more different than under AC-condition. The aim of our investigations is a realistically determination of particle movement in a small scale set up with gas filled test vessel. An appropriate electrode arrangement was designed in order to achieve a similar utilization factor of a real size arrangement. To get an optimized field distribution, simulations by a FEM-program were undertaken as well as different electrode forms were used in the experiments. Experiments were carried out with different sizes of particles at different gas pressures with SF 6 -gas. In order to get a correlation between particle movement and partial discharge activity, a camera was synchronized with the PD-measurement. Finally statistical evaluation of the lift-off field strength was made for both polarities.
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