Research Of Voltage Sag Source Detection Technology In Chinese Distribution Network

Today, the proportion of sensitivity electricity power load is increasing largely and the grid power quality requirements of customers can not compare with the previous. Among all the power quality problems both the energy supply sector and energy users care, Voltage Sag is now ranked very front. Statistics showed that 90% of the customer complaints about power quality are a direct result of or related problems caused by voltage sag. From early 1990s, the voltage sag began to be used as an important indicator of the quality in some developed countries and research work relevant to voltage sag started. Since then, research of voltage sag has become an important branch of power quality, and voltage sag source detection is an important procedure to solve voltage sag problems.Voltage sag source detection is to determine the voltage sag source located upstream or downstream of the PQ monitors, thereby facilitating further measures and defining responsibility. Various voltage sag source detection techniques can be summarized into two categories:the first is designed for the voltage sag source localization specially and can be called power quality based method; the second modified the existing protection strategies in order to locate voltage sag source, which can be called relay protection based method.A method to determine the location of voltage sag source, which is based on the theory of incremental impedance, is proposed in this paper. We summarized current research of voltage sag source detection. Then, the incremental impedance theory and how to detect voltage sag source in distribution network are introduced. For some asymmetry faults which will not result obvious change of positive components, the detection method based on real part of incremental impedance can not locate voltage sag source correctly. To solve this problem, according to features of voltage sag source of different types, the criterion of voltage sag source detection is summarized. The positive and zero sequence criterion of fundamental and the fifth harmonic for different voltage sag sources are analyzed. The voltage-sag-source detection strategy is accomplished after the analysis of voltage sag ride through capability of distribution transformer. The method has clear physical theory. It is easy to apply for real system and effective for both linear and nonlinear load. The results of MATLAB simulation and simulation experiments verify the criterion.