Analysis,Estimation And Mitigation Of Power System Voltage Sags

Voltage sags has been recognized as one of the most important power quality problems, due to its effects on normal and safe operation of many customer's sensitive loads of the power utility. The lost is so huge that voltage sags has been widely concerned all over the world, especially in some developed countries. In today's liberalized electrical market, the higher requirement has been put forward to power quality. The characteristics of voltage sags are analyzed firstly, then the thesis studies the following problems: Firstly, the monitoring and investigation of voltage sags has been done. Unbalanced voltage sags and all kinds of voltage sags are also analyzed in theory. A new method, which can distinguish from all kinds of voltage sags and estimate the characteristics of voltage sags by measured RMS voltage, is proposed. Compared with the realistic measured results, the efficiency of the proposed method is verified. Secondly, stochastic assessment of voltage sags is studied and a new method for multiple-meshed network is presented. The exposed areas can be plotted using this method, and then evaluation of magnitude and frequency of sags can be done for any special load node in network. As an example, the IEEE 30-node system has been calculated and the results been analyzed. Besides, Combined with interval equations, a method to plot the exposed areas under the condition of every component's parameter in a network permitted change in certain range is introduced. And take a 24-node system as an example to do the work. Finally, mitigation of voltage sags is given. There are all kinds of reasons causing voltage sags. The monitoring and investigation of voltage sags of local power system can provide some significant references for establishment of national voltage sags standards,optimization design of local power system and equipment manufacturer determining design strategy. It is pivotal for power utility,power users and equipment manufacturers clasping to solve voltage sags problem. It can make voltage sags effects on sensitive equipment minimize.