Distribution System Reliability And Security Evaluation Based On Matrix Analytical Calculation

The power distribution system directly faces the end users,which is related to the continuous safe and reliable power supply for power users.Distribution system reliability and security analysis is the basic work of distribution system planning and operation,its essence is the traversal analysis of all fault scenarios of distribution system.The existing fault traversal mode based distribution system analysis method search process is cumbersome and inefficient.The core and difficulty of efficient analysis of power distribution system lies in how to calculate and analyze the reliability and security indexes by means of analytical expression,which can help identify the weak links of the system while improving the calculation efficiency.Therefore,this paper mainly carries out the following research work from the aspects of hierarchical correlation model construction,reliability index analytical calculation,N-1 analytical verification and weak link identification,etc.:(1)The multi-level incidence matrix model system of node-branch,feeder-feeder,main transformer-main transformer and substation-substation of power distribution system is constructed to express the correlation and influence relationship between source and load of power distribution system at multiple levels,and the relationship between different levels of incidence matrix is given.The established multi-level association model of distribution system lays a model foundation for the subsequent analytical calculation of reliability and security of distribution system.(2)The analytical calculation of distribution system reliability index and weak link identification method based on incidence matrix are proposed.Firstly,based on the form of a series of incidence matrices,such as node-branch incidence matrix,sourceload supply path matrix,contact incidence matrix and classified fault influence matrix,the influence range and influence degree of component faults at different locations of distribution network on all system loads are expressed analytically.Furthermore,the element assignment operation and matrix operation of the fault influence matrix are used to calculate the reliability index of distribution network at one time,so as to realize the analytical calculation of the reliability index of distribution system,and the sensitivity value is calculated by partial derivative transformation and perturbation transformation to locate the weak links affecting the system reliability.The proposed reliability analytical calculation method avoids repetitive search in the process of fault enumeration,saves calculation time,improves calculation efficiency,and assists in the accurate identification of weak links,which can provide reference for the targeted improvement of power supply reliability.(3)The method of N-1 verification and weak link identification of main transformer in distribution network based on incidence matrix are proposed.Considering the load transfer mode when the main transformer fails,the load transfer matrix,the main transformer capacity matrix and the tie line capacity matrix are constructed.By comparing and calculating the difference between the load to be transferred from the N-1 main transformer and the maximum transfer capacity of the associated supporting main transformer,the N-1 verification result of the main transformer of the whole network is obtained at one time,and the analytical expression of the N-1 verification of the main transformer is realized.The weak link of N-1verification of main transformer is identified by transfer margin matrix.The proposed N-1 analytical verification method of main transformer avoids the tedious repeated search operation,improves the efficiency of N-1 verification,and gives the weak links of N-1 verification,which can provide necessary reference information for optimal planning of distribution network.In conclusion,the analytical calculation method of distribution system reliability and security proposed in this paper provides an innovative calculation method for comprehensive evaluation of safe and reliable power supply of distribution system,improves calculation efficiency,identifies weak links,and provides reference for optimal construction of distribution network.