外文翻譯--svc與statcom在電力系統(tǒng)中應(yīng)用的效益(文件)
【正文】 l is realized. Other possibilities are fixed capacitors (FCs), and thyristor switched reactors (TSRs). Usually a dedicated transformer is used, with the pensator equipment at medium voltage. The transmission side voltage is controlled, and the Mvar ratings are referred to the transmission side. The rating of an SVC can be optimized to meet the required demand. The rating can be symmetric or asymmetric with respect to inductive and capacitive reactive power. As an example, the rating can be 200 Mvar inductive and 200 Mvar capacitive, or 100 Mvar inductive and 200 Mvar capacitive. B. STATCOM The voltagesourced converter (VSC) is the basic electronic part of a STATCOM, which converts the dc voltage into a threephase set of output voltages with desired amplitude, frequency, and phase. There are different methods to realize a voltagesourced converter for power utility application. Based on harmonics and loss considerations, pulse width modulation (PWM) or multiple converters are used. Inherently, STATCOMs have a symmetrical rating with respect to inductive and capacitive reactive power. For example, the rating can be 100 Mvar inductive and 100 Mvar capacitive. For asymmetric rating, STATCOMs need a plementary reactive power source. This can be realized for example with MSCs. VII. THE FUNCTIONAL RATING CONCEPT Traditionally, SVCs of a mon design have been used to handle different types of work problems. The trend today, however, is to tailor SVCs for their intended use. This is important in order to make SVCs cost efficient. For steady state voltage support, ., to follow the daily load pattern, bulk reactive power bined with stepless smooth voltage control is desired. Vernier voltage regulation can be provided by a TCR running in parallel with harmonic filters. The bulk reactive power is provided by mechanically switched capacitor banks (MSCs) or reactors (MSRs) governed by the SVC controller. Thus SVCs serve the purpose of continuously maintaining a smooth voltage, piloting the MSC switching. If the task is to support a system limited by post contingency voltage instability or unacceptable voltage levels, a large amount of quickly controllable reactive power is needed for a short time duration. An SVC with additional TSCs is an excellent choice. Post recovery voltage support may also be necessary—this is then preferably provided by MSCs governed by the SVC. 3 For temporary over voltages, large inductive reactive power is needed for a short period of time. The standard TCR has some shorttime over current capability. This capacity can easily be extended by lowering its steady state operating temperature and by ―under sizing‖ the reactors. A. Enhanced SVCs The SVC characteristic at depressed voltage can be efficiently improved by adding an extra TSC. This branch is intended to operate only during undervoltage conditions. It can be added without introducing additional cost in other parts of the SVC. Most important is that the current rating or the voltage capability of the power transformer does not need to be increased. Power transformers allow large overcurrent during limited time (IEEE C57115 can be used as a guide for available capacity). In many cases three times overload in current for 10 seconds is available. The additional TSC rating is typically in the range of 50 to 100% of the SVC rating. B. SVC Short Term Overload The maximum power from an SVC at a given voltage is determined by its reactance. No overload capacity is available unless the reactance is lowered, ., by adding a TSC. For overvoltages, however, the SVC reactance is no longer the limiting factor。 at even multiples the level
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