Voltage Sag Detection And Reliability Assessment In Urumqi Power Distribution Network

With the rapid development of information technology and other high-techs, a number of equipments which are sensitive to short disturbance of voltage magnitude have been put into use, the problem caused by voltage sag have attracted much attention in the world. Up to now, many research works have been done on voltage sag around many aspects.The paper introduces the power quality and current studies in china and foreign countries, especially describes the definition, causes, characteristic quantities of Voltage Sag, and some techniques to reduce the effect of voltage sag on customers are also analyzed. Then this paper studies the following two questions:1) Analyzing the methods of voltage sag source location;2) Assessing the reliability of voltage sag in distribution network.For the voltage sag location methods, in this paper, analyzed current methods published in some magazines. The paper proposed to detect voltage sag source location by the method called real current component, which needs to know the magnitude of current and power factor angle at every monitoring point, the product is plotted against time. The product polarity is used to indicate the direction of voltage sag source either it is from upstream or downstream. This method is simulated in a single-source system and two-source system, and considering balanced and unbalanced fault.For the assessment of reliability in power distribution system base on voltage sag, this paper develop a practical approach, named"step by step analysis", and the method in which conventional short-circuit tool have been associated with failure rates of transmission line and in advanced reliability calculus. The reliability prediction methodology allows both the utility and end-users to objectively and quantitatively assess the impact of voltage sags on electric systems.