Research On Distribution System Security Region For Smart Grid

As a power system which supplies electric power for customers directly,distribution system plays an important role in ensuring the continuous power supplyfor customers in safety and in high reliability, so scientific estimate and verification ofdistribution security is meaningful to ensure distribution networks operating securelyand efficiently. Smart grid will change distribution system thoroughly, fast loadtransfer between transformers will be a new boundary condition of security, on which,when transformer N-1contingency occurs, load can not only be transferred betweentransformers, but also transferred by switches of networks, which providesfundamental theory for building distribution system security region. This paperintroduces development of distribution system security and regions and flow of N-1criterion. The definition of distribution system security is given, and the mathematicalmodel of distribution system is also built. The calculation of security boundary is setup. Finally these are all verified by a case.First, this paper introduces the definition and mathematical expression of DSSRaccording to the security region in transmission system and N-1security criterion. Toprove the existence of security boundary and introduce its topological characteristics,this paper uses N-1security test to simulate the dividing phenomenon of distributionsystem security, and designs an N-1fitting approach point by point to describesecurity boundary. Then by simulating2-dimensional security boundary of differentfeeders, topological characteristics of security boundary are induced and summarized.Second, distribution system security model based on transformer interconnectionsis introduced, and based on the model above distribution system security model basedon feeder interconnections is proposed. In contrast, the model of feederinterconnections can both satisfy transformer N-1and feeder N-1, and accurate toload of feeders, which is more accurate. Method of contrast and verification betweensecurity region and N-1security testing is designed. In contrast, the securityboundaries computed by model and N-1fitting are the same.Third, the applications on security assessment and control of distribution systemsecurity are analyzed, and the method of security estimate and control are given,which is also in verified by N-1security testing. Finally, the case study has shown the application of the DSSR model, existence ofsecurity boundary and regions, which proves the applicable values and accuracy ofthe proposed DSSR model and calculating method.