Research On Configuration Strategies Of Low Voltage Release For Voltage Sag Sensitive Equipment

With the continuous progress of science and technology,the proportion of all kinds of high-end equipment in the power grid is gradually increasing.The requirements for power quality are becoming more stringent.As a power quality problem,voltage sag has caused huge losses to users.Low voltage release is widely used in distribution network.Voltage sag may cause misoperation and cause load outage in the whole area.Therefore,it is of great signif icance to configure the low voltage release reasonably.The distribution characteristics of system voltage sag will affect the coordination effect between equipment and low-voltage release.Accurate prediction of system voltage sag is the basis for further configuration of low-voltage release.In this paper,a multivariable probability model of system short-circuit fault is established.Latin hypercube sampling is used to simulate the system short-circuit fault,and the voltage sag of each node of the system is estimated.Comparing the prediction results of Latin hypercube sampling method and Monte Carlo method,it is proved that Latin hypercube sampling has better stability and convergence.According to the tolerance characteristic curve of sensitive equip ment and low-voltage release,the uncertainty model of failure or action probability is established to evaluate the operation state of sensitive equipment and low-voltage release under the influence of voltage sag.Based on the position of their tolerance curves,three kinds of coordination relations are defined.On the basis of analyzing the characteristics of different coordination relations,the concept of coordination index of sensitive equipment low voltage release is put forward.The coordination index of different types of sensitive equipment and low-voltage release is calculated.Through the comparative analysis of the calculation results,the effectiveness of the index proposed in this paper in the low-voltage release configuration strategy of sensitive equipment is verified,which can evaluate the coordination effect of low-voltage release and sensitive equipment,and provide theoretical guidance for the configuration of low-voltage release.In order to solve the problem that it is difficult to determine th e characteristics of equipment or release tolerance in the uncertain interval,a method based on evidence theory is proposed to evaluate the coordination effect of sensitive equipment and low-voltage release.The result of the algorithm is compared with th e index proposed in the third chapter,which proves that the algorithm has good evaluation effect on the coordination of sensitive equipment and low-voltage release.At the same time,the algorithm does not need to know the prior probability assignment,an d avoids the assumption of probability density function.Compared to coordination index,it has better applicability in practical engineering.