In the context of escalating demand for electrical energy and the ongoing development of electric power plants, power system expansion studies are needed. Notably, transmission expansion planning stands as a pivotal endeavor within this domain. In this study, the main goal is to reinforce and expand the transmission network subject to network operation constraints, budget constraints, and available technologies in such a way that electrical energy demand through the planning horizon is supplied to all consumers reliably and indiscriminately. In this thesis, the transmission expansion planning predicament for the designated future year is addressed. The primary aim is to simultaneously minimize investment and operating costs, while elevating the reliability of energy supply. The expected energy not supplied is eva‎luated, considering the N-1 contingency criterion for all transmission equipment and power generation units, as well as the N-2 contingency criterion for the most severe double contingencies. The investigation considers a scenario where the capacity and siting of new power plants are pre-established, and the load is characterized using a three-step load duration curve. Two modeling approaches are proposed for the transmission expansion planning problem. First, the traditional modeling based on DC power flow equations is presented and its results are investigated. The formulation of this problem leads to a mixed-integer linear programming framework. This modeling approach incorporates certain approximations and simplifications, a facet that is duly illustrated in the ensuing numerical findings. The second modeling approach is founded upon AC power flow equations, embracing considerations for reactive power, losses, and voltage-related constraints. A proxy of reactive power planning model is also considered in the second approach. Therefore, the second modelling approach results in a large-scale nonlinear optimization problem. In pursuit of a globally optimal solution, the AC power flow equations are tactically relaxed and cast as second-order cone constraints Consequently, the second model is presented as a mixed-integer second-order cone programming problem. It merits acknowledgment that the inclusion of all N-1 and the most severe N-2 contingencies substantially inflates the scale of the optimization problems in the aforementioned approaches. Ergo, solving the DC power flow-based model for large-scale networks becomes very time-consuming. On the other hand, the AC power flow-based model for large-scale networks becomes even intractable. By employing Benders decomposition technique, the proposed planning models are decomposed into a master problem and some subproblems, which are solved iteratively within an acceptable time frame. The proposed transmission expansion planning models are implemented on the six-bus Garver and 118-bus IEEE standard test systems using the GAMS software. Through multiple numerical case studies, the capabilities of the proposed models are investigated.

محمد امين لطيفي

محمداسماعيل همداني گلشن , محمد ابراهيمي