Voltage Sag Probability Analysis And Risk Assessment Of City Power Grid

With the rapid development of the city’s economy, city power grid access more and more equipment. For power supply companies, the systems become more complex, the various factors that affect the stability become more and more;for the power consumer, a variety of frequent power quality problems began to directly affect their economic benefits. As the most important power quality problems, Voltage sag began to receive more and more attention. Research on voltage sag problem have great significance both for the supply business or power consumers. This paper analyzes the megacities power grid voltage sag problem, including the analysis of the various factors affecting the node voltage sags, calculate the probability distribution of the node voltage and evaluated the voltage sags of the city power grid.Analysis of voltage sag factors are: by analyzing the principle of voltage sags we find that short circuit, operating large induction motor starting and transformers are the main cause of voltage sags. Then compare the effects of these three factors on the grid, and make further studies of the glass which is the most influential factor. This paper presents the concept of a line fault influence coefficient. We use the coefficient to adjust the failure probability of line.Research on the calculation of the probability distribution of the node voltage are: the study of the analytical formula algorithm about voltage sags; On the basis of this algorithm, combine line failure probability, the probability of failure of various types, we propose a method to calculate the probability distribution of the node voltage.Research on voltage sag assessment are: the introduction of the current system voltage sag major evaluation index; proposed to assess the risk of voltage sags based on the load loss; combined load loss model and the probability distribution of the node voltage, we can calculate the risk value of every node.