2215300mw火力發(fā)電廠設(shè)計(jì)電氣工程及其自動化畢業(yè)論文外文文獻(xiàn)-資料下載頁
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【正文】 it is prone to pieces of the system being damaged when relays fail to operate properly. With microprocessor based relaying schemes, a hybrid reliability focus is attainable through adaptive relaying. Adaptive relaying describes protection schemes that adjust settings and/or logic of operations based on the prevailing conditions of the system. These adjustments can help to avoid relay missoperation. Adjustments could include, but are not limited to, the logging of data for postmortem analysis, munication throughout the system, as well changing relay parameters. Several concepts will be discussed, one of which will be implemented to prove the value of the new tools available. Power Systems History The distribution of electricity in the United States of America can be traced back to September 4th, 1882, when Thomas Edison opened the Pearl Street Station in lower 14 Manhattan. Serving about a quarter of a square mile, this direct current (DC) system was primarily used for lighting in the financial district of New York. Edison showed that it was possible to efficiently provide electricity from a central generating station. The issue with DC systems was that the end consumer had to be located within a few miles of the generating station. The problem was that the low voltage used with this type of distribution led to higher currents and higher losses on the lines used to distribute the electricity. This forced the generating plants to be small which reduced efficiency, and it meant that only small distribution systems in densely populated areas would be effective [1]. In distribution systems the voltage is held constant and the current flowing through the lines depends on the load being served. The losses associated with the lines used to distribute the electricity vary with the square of the current running through the lines. So if the current through the lines doubles, the losses associated with the lines actually quadruples. At the time Edison started implementing his systems, there was no way to easily change the voltage in a DC system. The ability to vary the voltage of the distribution lines would allow for the reduction of current during transmission, which was being developed within alternating current (AC) systems. AC allowed for transformers to increase the voltage required by transmission and a reduction to a voltage level that is safe for end consumers to use。 this significantly reduces the losses of sending electricity over longer distances. Nikola Tesla was the pioneer of this AC technology as well as the concept of polyphase distribution [1]. These peting strategies of electrical distribution, AC and DC systems, led to what is monly known as the Battle of the Currents. Thomas Edison, owning the patents for DC systems, argued that AC and the higher voltages associated with it was unsafe. At the same time, however, Gee Westinghouse was building AC transmission lines that stretched for miles. This, along with Nikola Tesla’s development of an AC motor among other developments, led to the ultimate victory of AC systems. This victory of alternating current led to the electrical distribution system we have today in which large generating stations delivering power over long distances at high voltages, which is both economical and efficient 15 in parison to the original DC systems [4]. This did, however, lead to several engineering issues to which solutions are still being developed today. The AC system pioneered by Westinghouse and Tesla has developed into one of the most plex machines in the world. The growth started with many small independent systems. For reliability purposes, these systems were interconnected. This interconnection of many small systems meant that the number of machines necessary for reserve operation during peak loads was lowered. The interconnection also enabled utility panies to get the cheapest possible power from their neighbors. These interconnections grew into the massive system which we have today. There are issues that arose with the creation of this massive system。 these issues include higher fault currents, cascading failures in which multiple smaller systems are affected when the problem only occurred in one of them, and a very delicate balancing act that occurs between systems. The planning that goes into t
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