Researches On The Critical Components Set Affecting Distribution System Security

Distribution system security analysis is mainly based on N-1 guideline.Distribution system security region(DSSR)theory and total supply capability(TSC)theory show the maximum range allowed to be operated and maximum capability of supplying loads,which are the important basis of distribution system security analyses.Presently for the distribution network in China,it is an urgent task to improve efficiency of reliable and safe supplies for loads.Targeted for the critical components in the distribution system,the thesis further extends the theory on DSSR and TSC,studies the security region and power supply capability under constraints of certain components N-1,and gives the definition,evaluated indice and the solving method of the critical sets of components,which provide a new thought of improving the distribution system security.Fisrtly,the basic concept and mathematical model of DSSR and TSC are introduced.The definition and mathematical model of partial distribution system security region(DSSR_p),partitial total supply capability(TSC_p)and partial average boundary supply capability(BSC_p)are proposed.The contrasts between the two models are analyzed.The methods of evaluating distribution system security which are based on power supply capability and security region are concluded.Secondly,it is found that the results of the changed TSC and DSSR are various,depending on different combinations of the components in N-1 fault sets.Therefore,the critical N-1 fault set of componets is defined.Based on the sensitivity analytical approach,the indices that evaluate the critical sets of components are proposed,including three sensitivity indices and the weighted indice.Then,a practical method of determining the crtical sets of components is proposed:First,traverse all components and calculate the sensitivity of DSSR and TSC;then rank the sets according to the weighted indice;lastly,screen out the critical sets judged by the threshold value.Finally,the concept and method given in the thesis is proved to be valid by the test case.In the test case,the changes of DSSR and TSC under constraints of certain components N-1 are analyzed.It is conluded that the critical components set has the basic feature,including N-1 load-transferred structure,multi-connection structure and relatively large component capacity.Furthermore,the thesis initially discusses the mechanism of the critical sets of components and analyzes the network structure and component capacity's impacts on the critical components set.If the components in the critical set screened out by the proposed method are strengthened and the reliability will be improved,approximately assuming that N-1 fault of the components can hardly occur,the volume of DSSR and TSC will be enhanced greatly.It is a novel way to improve safety and efficiency of distribution network.