Situation awareness (SA) refers to the process of perception, comprehension, and state projection of the system, elements, and environmental factors within a volume of time and space. The security assessment is an important part of SA for distribution networks. In this paper, the distribution system security region (DSSR) is used for SA for the first time, and a security SA method based on security distance (SD) is proposed. First, based on the existing DSSR, which is defined as the set of all

more »

... perating points (OPs) satisfying N − 1 security criterion, this paper supplements the N − 0 DSSR satisfying normal operating constraints. Second, calculate SDs between the OP and security boundaries to determine whether an OP is secure. If one is secure, its SDs can give the security margin; while if one is insecure, its SDs can give the degree of insecurity and the fault, or the overload components can be recognized via the cross security boundary analysis. The situation comprehension for the distribution network security is realized through the above-mentioned information. Third, the security level of distribution networks in the future can be predicted by the trends of SDs. Finally, the feasibility and effectiveness of the proposed method are verified by an actual distribution network case.