Identification and calculation of static frequency characteristics is of great significance for power system to maintain its stability. In this paper, coefficient of static frequency characteristics is fitted by the least squares method. Frequency deviation restriction point under different capacitances is forecasted by the fitted trend of coefficient of static frequency characteristics. Moreover, the new method is simulated and its calculation error is also compared.
Aiming at how to solve the question of quantitatively distinguish negative damping low frequency oscillation and forced power oscillation, the difference in frequency and damping ratio between the two kinds of oscillations have been discovered through mechanism analysis, and a new quantitative distinction criterion for the property of the low frequency is proposed. The oscillation data is windowing identified by ARMA model based on weighted recursive least squares algorithm dynamically, and low frequency type can be distinguished according to the changes of oscillation frequency and damping ratio during the oscillation. The simulative results have shown that the method is feasible and effective.
There are many uncertainties in power system. It is significant to consider the impact of uncertainties when comparing the importance of lines. The fuzzy set theory was applied and the fuzzy load flow calculation on the basis of line outage which had taken into account the generator output and load uncertainties were deduced. Overload, low voltage, and load shedding were selected as risk indexes. Then combined with the severity functions in the risk theory, the risk assessment models based on fuzzy membership have been put forward. Finally, the results of the three indexes and their comprehensive risk index about IEEE 118-bus system were given, and then the importance of each line in the system was compared, which confirms the value of the approach introduced in this paper.
From the risk theoretical point of view, static security risk indicators of the transmission grid are built on the basis of the probability theory, grid static security risk indicators, including overload risk indicators and voltage-limit risk indicators. For both risk indicators, the probability of the outage of one line is considered, as well as in the case of the uncertainty of the power system the serious consequences caused by the outage of one line. And the overload risk assessment model and voltage-limit risk assessment model are built. Finally, quantitative assessment and calculation are done through the standard system examples of these two static safety risk indicators, then assess and sort the transmission lines of the importance based on the simulation results.
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