外文翻譯--svc與statcom在電力系統(tǒng)中應(yīng)用的效益-展示頁(yè)
2025-05-27 08:23本頁(yè)面
【正文】 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。 instead the current in ponents defines the limit. In most cases the thyristors set the limit. The design is made so that the thyristors are running at a maximum allowed temperature at maximum steady state system voltage. A margin to destructive temperatures is reserved in order to handle fault cases. The Forbes 500 kV static var system near Duluth Minnestoa USA is an interesting example of an Enhanced SVC [5]. VIII. HARMONICS Both SVCs and STATCOMs generate harmonics. The TCR of an SVC is a harmonic current source. Network harmonic voltages distortion occurs as a result of the currents entering the power system. The STATCOM is a harmonic voltage source. Network voltage harmonic distortion occurs as a result of voltage division between the STATCOM phase impedance and the work impedance. The major harmonic generation in SVCs is at low frequencies。 at even multiples the levels are lower. The harmonic generation decays with increasing 4 frequency. STATCOMs might also generate harmonics in the same spectra as the conventional SVCs. The magnitudes depend on converter topology and the modulation and switching frequency used. In most cases STATCOMs as well as SVCs require harmonic filters. IX. FOOTPRINT More and more frequently the footprint available for prospective STATCOMs or SVCs is restricted. The trend is, as in many other fields, more capacity on less space. Requirements for extremely tight designs, however, result in higher costs. In general the footprint issue seems not to hinder the utilization of STATCOMs or SVCs, but occasionally, STATCOM has been preferred based on anticipated smaller footprint. When paring SVCs with STATCOMs, it is tempting to assume that the latter will fit within a much smaller footprint, as the passive reactive elements (air core reactors and high voltage capacitor banks) are ―replaced‖ with semiconductor assemblies. In the authors’ opinion, this assumption however remains to be practically proved. The main reason for this is that the voltage sourced converter concepts applied in STATCOMs to date have been built with several (even as many as eight) inverter bridges in paral
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