A new formulation for power system reliability assessment with AC constraints

• A new formulation for composite system reliability assessment is proposed.
• The new formulation relies on an approximated AC power flow model.
• The new model is linear and more attractive in terms of computational burden.
• Accuracy of the model is compared with that of the conventional methods.
• Performance of the model in different conditions is shown by sensitivity analyses.

Recent investigations have revealed the significant role of reactive power in blackout events. The associated disturbances frequently emerge in the form of voltage instability and collapse. Due to the computational complexity of modeling and analysis of enormous contingencies, DC approximation of the power flow, without accounting the role of reactive power, is usually used to evaluate the contingencies and to mitigate the associated probable violations. This paper, at first, presents a linear power flow model based on an approximated version of AC power flow formulation. The proposed model is then used to develop an efficient reliability assessment approach which is capable of taking both active and reactive powers into account. The analysis technique is based on the linear programming format which leads to an optimal solution within a short computation time. Voltage and reactive power violations as well as transmission system overloads are alleviated by generation rescheduling or load shedding as the last resort. Numerical tests on the IEEE-RTS and the Iranian power grid show the acceptable accuracy of the results along with a significant reduction in the computational effort. Various sensitivity analyses are also investigated to reveal the robustness and performance of the proposed model.