Research On Weak Point Identification And Risk Assessment Methods Of Urban Distribution Network

The safe and reliable power supply of urban distribution network is a very important part of the power system.Today,however,the probability of a power outage or power loss due to a distribution failure is about 80%.With the rapid development of social economy,electric load is increasing rapidly.Therefore,distribution network of power supply reliability and power supply quality more strict requirements are put forward.Therefore,how to identify weak links in distribution network and to conduct the risk assessment of power distribution network operation,to improve the distribution network structure,has become a key task.This thesis first expounds the research status of the operation level of urban distribution network,and points out the necessity of weak point identification and risk assessment of the distribution network.Based on the complex network theory,proposed to improve the distribution network node degree,line degree,node betweenness and line betweenness.Combined with the risk theory of the node voltage limit and line overload and the calculation results of power flow,weak links in distribution network nodes and lines are searched respectively.Then the comprehensive vulnerability index of distribution network node and the comprehensive vulnerability index of line are established.The effectiveness of this method is verified by an IEEE 33 node instance.The operation risk of distribution network is divided into three aspects: load point loss risk,node voltage over-limit risk and line over-load risk.In order to accurately and quantitatively analyze the loss of each load point caused by equipment failure.In this study,the fuzzy relationship between equipment failure rate and equipment state is utilized,and the failure rate prediction model of distribution network master equipment is determined based on the uncertainty reasoning of cloud model theory.Then the health condition correlation cloud of each device and the failure trend cloud of possible failure occurrence are established.The real-time failure rate of the main equipment can be obtained by inputting the health index of the main equipment in the distribution network into the cloud.So The quantitative load point loss risk is obtained by multiplying the load point failure rate which is the sum of the failure rates of all the equipment on the minimum path with the consequence function of power loss.On the basis of the above established comprehensive vulnerability index of node and line,the risk severity function is established according to the characteristic that the risk of distribution network increases exponentially with the gradual increase of over-limit and over-load degree.Then get the node voltage out of limit risk model and the line overload risk model by multiplying it by the probability function.Finally,the load point loss risk,node voltage over-limit risk and line overload risk are weighted by AHP,and the comprehensive risk model of distribution network is proposed.The risk assessment method can identify the weak links of distribution network from three aspects and quantitatively analyze the operation risk of distribution network.Through the example analysis,it is verified that the proposed risk assessment method is consistent with the actual situation and has the feasibility and rationality.