A Research On Power System Static Security Assessment Method Based On Risk Theory

With the rapid social and economic development, a variety of new problems beginto emerge and pose a serious threat to the security of power system. In the first place, thereformation of electric market would create a new environment of competition for powersystem. Economic gains would become the ultimate goal for power producers, power gridcompanies and power users when making decisions. This adds to the uncertainty ofpower system operation. Furthermore, with the climatic change and green house effect,adverse weather conditions occur more often. The large-scale ice disaster in southernChina in early2008and serious blackout accidents caused by extremely adverse weatherlike typhoon in North America in recent years are warning us of the effects that climatecould have on the steady and safe operation of power grids. Finally, because fossil fuels,such as coal, petroleum and natural gas, are running out of supply, traditional energysources can hardly satisfy the need of the development of society. Meanwhile, windpower generation have many advantages over fossil fuels. For one thing, wind energy isan inexhaustible energy source. For another, wind power produces no pernicious gas. Sowind power becomes an important alternative when the world is faced with severeshortage of energy sources. However, as large-scale wind farms are connected to powersystems, the intermittency and uncertainty of wind energy have a significant impact onthe security of power grids. In order to cope with these new problems and help systemoperators grasp the security level of the power system and take proper measures toachieve preventive control, an efficient and scientific method for power system securityassessment is urgently needed.The traditional way of assessing the security of power system lays emphasis on themost serious and credible accident, and cannot take into consideration the probability andseverity of accidents. The probability assessment method still cannot deal with theconsequence of an accident. Power system static security assessment based on risk theoryis able to take the probability and severity of a fault into account, and evaluate thesecurity level of power system scientifically and comprehensively. This paper mainly focuses on the basic concepts, models and methods of powersystem static security risk assessment. The two sub-problems of static security, i.e.transmission line overload and low-voltage are discussed. To cope with the first newproblem mentioned above, power users’ outage loss is introduced as the economic riskindex to consider the influence of the power market environment. Secondly, atransmission line model considering the effects of weather conditions is constructedbased on the fuzzy inference theory. Finally, the wind farm model is establishedconsidering the wake effects. The cases in which wind farms are directly connected to theoriginal power system and in which wind farm replaces traditional power source withequal capacity are assessed and analyzed.