Security Region and Power Supply Capability for Distribution System Under Normal Operational State: Definition, Model, and Application

Existing distribution system security region (DSSR) and total supply capability (TSC) are under N - 1 security. This paper proposes definition, model, and application of security region and power supply capability for active distribution networks under normal operational state (N - 0 security). DSSR and TSC under N - 0 security are named as DSSR0 and TSC0, respectively. First, motivation to study DSSR0 and TSC0 is clarified. Then, definitions and mathematical models of DSSR0 and TSC0 are introduced for active distribution networks and flexible distribution networks with soft open points. DSSR0 is the set of all operating points satisfying normal operational constraints and describes maximum allowable operating range of distribution network. All operating points inside DSSR0 are secure, while all operating points outside DSSR0 are insecure. TSC0 is maximum load supply capability that satisfies normal operational constraints of a distribution network, and its connotation is the same as loadability. TSC0 curve is an extension of TSC0. It is composed of total load of boundary points in ascending order and describes complete power supply capability of a distribution network. Next, for urban distribution network with distributed generation in China, the analytical algorithm of DSSR0 and TSC0 is proposed. Furthermore, a drawing method of the TSC0 curve is proposed. Meanwhile, effectiveness and scalability of the proposed method are verified by IEEE RBTS BUS4 case and the modified IEEE RBTS case. Differences in security region and power supply capability between N - 0 and N - 1 security are analyzed. Finally, application cases in both operation and planning are demonstrated. The proposed DSSR0 and TSC0 can help dispatchers obtain feasible operational boundaries, which is the “bottom line” for operation of a distribution network.