In view of the smart distribution grid requirements on fault detection

a distributed regional longitudinal protection system is proposed. The system structure and workflow are described

and the protection area dividing principle for the regional longitudinal protection system is studied. On this basis

an online associated area determining method for distributed regional longitudinal protection is proposed. A nodes-branch incidence matrix is adopted to describe the network topology

with a transformation matrix generated from the current nodes-branch incidence matrix. Then the adjacent matrix can be calculated by multiplying nodes-branch incidence matrix and transformation matrix. The regional longitudinal protection associated areas can be rapidly and reliably determined by analyzing this adjacent matrix. In addition

the effects of changes in the topological structure of network on the associated area determining method are discussed. Finally

a case study is given to validate the method described above.