Critical contingencies-aware conic AC transmission network expansion and reactive power co-planning

Economic and environmental constraints limit new transmission line installations, forcing operators to maximize existing infrastructure utilization while considering voltage support, AC power flow (ACPF) equations, and N-1 reliability, which significantly increase computational complexity. This paper presents a computationally efficient model and solution approach for static transmission network expansion planning (TEP) based on ACPF equations and incorporating the N-1 reliability criterion for active and reactive power supply. To improve efficiency, a reactive power planning (RPP) proxy is integrated into the model to reduce unnecessary line expansion by coordinating reactive power source deployment. The problem is formulated as a mixed integer second-order cone programming (MISOCP) model, factoring in contingencies across all existing and candidate transmission lines. Only a small subset of transmission line outages results in operational constraint violations. Therefore, ensuring reliability for critical contingencies suffices, as considering all increases complexity. Thus, a critical contingency screening approach is proposed in which critical cases are identified by sequentially solving a master problem and sub-problem. The master problem resembles the original MISOCP, but includes only a subset of contingencies, gradually expanded through iterations. The sub-problem uses bi-level Max-Min optimization to screen the worst contingencies causing the worst operational constraint violations. These worst contingencies are progressively added to the master problem, ensuring the final subset accurately represents the full set of contingencies upon convergence. Numerical results on Garver and IEEE 118-Bus test systems demonstrate the proposed approach’s efficiency in solving the proposed TEP model within the acceptable time frame.