The theory of self-organized criticality explores the behavior of large complex systems in conditions that are neither stable nor unstable, but critically stable. When such conditions arise in the power system, some initiating events, even minor, can trigger a chain of successive outages of system equipment, which mainly includes the transmission lines. The blackouts caused by cascading outages can lead to voltage collapse and a global blackout or pro‎mp‎t the system to reorganize into a new stable or critically stable state. Based on this theory, the OPA modeling method was developed to simulate the behavior of the power system in self-organized criticality condition in collaboration with several reputable research institutes. In this method, the long-term evolution of the system, including the load growth and the construction of new lines is considered. In the short term, it probabilistically models the impact of operator's remedial actions on the better performance of the system, such as generation re-dispatching and load shedding, through DC power flow analysis at each time step (typically one day). The output of this model is the list of tripped lines and the time series of curtailed loads in the probable blackouts. Using these results, the probability of curtailed loads, which usually has a normal distribution for small blackouts and a power-law distribution for large ones is estimated and the annual unserved energy as a measure of blackout risk is calculated. One of the first applications of the DC-OPA model proposed in recent years, is its use in the probabilistic transmission expansion planning (TEP). This approach aims to minimize the risk of cascading transmission line outages and resulting blackouts, in addition to the traditional objectives of classical TEP. In this thesis, this application is further explored and the power system behavior extracted as the AC-OPA form. This model is combined with the classic TEP model to consider the impact of the real aspects of power system including reactive power and bus voltage profiles in the planning approach. The proposed hybrid model is called TEP-AC-OPA and offers a multi-objective optimization approach for simulating transmission expansion planning. In this planning procedure, the predicted load growth in the planning horizon is met with the lowest investment cost while simultaneously minimize the risk of system blackouts. Furthermore, according to the economic, geographical, and environmental impacts associated with constructing new transmission lines, application of the Flexible Alternating Current Transmission System (FACTS) devices is considered as an appropriate alternative for TEP. Accordingly, the models of conventional and suitable FACTS devices such as SVC, TCSC, and UPFC are also integrated into the AC-OPA model and yields a new hybrid model, named FACTS-AC-OPA. This model is capable of estimating the impact of these devices, which are optimally installed based on specific objectives in a power system, on reducing the risk of cascading transmission line outages. For this purpose, firstly, by investigating into the economic aspects and operational range of various FACTS devices, TCSC is identified and introduced as the most appropriate and economical FACTS devices to reduce the risk of blackouts. Afterwards, through a bi-level planning procedure, the suitable scenarios for expanding and optimally placing TCSC devices are determined based on two algorithms. One algorithm enhances the power system's loading margin, using the epsilon constraint optimization method, and the other one identifies and ranks the vulnerable lines in terms of the occurrence of cascading outages, using the proposed FACTS-AC-OPA model. In the second step, by using the same FACTS-AC-OPA model, the long-term impact of each scenario on reducing the blackout risks caused by the cascading outages of transmission lines in the self-organized criticality conditions is estimated.

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محمود فتوحي فيروزآباد

محسن حمزه , حبيب رجبي مشهدي , زينب مالكي