An Optimal N-1 Secure Operation Mode for Medium-voltage Loop Distribution Networks Considering Load Supply Capability and Security Distance

Abstract With many uncertainties, such as intermittent distributed generations and time-varying loads, penetrated into distribution networks, the load supply capability operating point has not been sufficient to guide power system operation for no security margin guarantee. To address this fundamental problem, an optimal operation model for interconnected distribution networks is proposed in this paper with the consideration of both security and efficiency of systems. The uncertainty, a feeder or substation transformer N-1 contingency, is taken into account and conductor thermal constraints after feeder or transformer failure are also incorporated into the formulated multi-objective model. The nonlinear optimization model is solved by a hybrid algorithm combining normal boundary intersection and sequential quadratic programming. The optimal load distribution solution on feeders and transformers can be obtained, which provides a trade-off between two defined indices, load supply capability adequacy and variation coefficient of security distance. Compared with conventional distribution loadability, case studies carried out on a test distribution network and a real urban distribution system in China demonstrate the effectiveness of the proposed model and solving method. The N-1 security margin is verified when increasing load demand.