The importance of flexible power flow control in electric power transmission networks is increasing owing to many factors that have arisen. Sen Transformer (ST) is one of the attractive power flow controllers. It has a wide control range, independent active and reactive power flow control capability, and is economically attractive. However, it operates in stepwise mode, has limited operating points, relatively slow response rate, and suffers from compensation error. Motivated by the limitations of the ST, power transistor assisted ST (TAST) as a novel power flow controller is proposed in this paper. The TAST consists of a highly-rated ST and a lowly-rated AC chopper based transistorized ST (TST). This paper first points to the importance of transmission lines' power flow control and reviews available power flow control devices. It then introduces the proposed TAST, determines the ratings of the TST and the switching pattern of its choppers. Next, it demonstrates the steady-state performance of the TAST, determines its control limits, compares the TAST to the ST and the unified power flow controller (UPFC), and the different control strategies of the TAST. In this paper, the TAST is modeled in MATLAB/SIMULINK and tested in an equivalent two bus system and in the IEEE-14 bus test system. The work also demonstrates improvement of the response rate of the ST. Cost analysis of the TAST is also done and is compared to that of the equivalent UPFC. Based on the results, the TAST realizes continuous, error-free, more flexible operation, improved response rate, and low cost. Moreover, the TAST provides 14.62% wider power flow control range. In conclusion, the TAST's operational characteristics are closely comparable to that of the UPFC with the advantage of lower cost and extended control area.

In this paper, transmission lines overload alleviation for the Sudan National Grid has been performed. Resizing the transmission system components is not suitable during the operation. On the contrary, in that case, alleviation of the overloads by generation rescheduling is suitable and effective. Decreasing the generation station output relieves transmission line overload, but to maintain the power equilibrium, the output of other generation stations must be increased, making sure no additional transmission lines are being overloaded. A simple, efficient, fast, and accurate technique for the alleviation of line overloads by corrective generation rescheduling and load shedding is applied to alleviate the overloads. The method ensures that alleviation of the existing violations does not create any new violations. The load shedding is used as a last choice in cases when generation rescheduling has not completely alleviated the overloads. An overload that cannot be relieved by only rescheduling the generation is always due to weaknesses in the system design. The method gives good results for alleviating line overloads in cases of the most severe contingencies.

The wide use of power flow controllers (PFCs) in transmission and distribution grids is becoming imperative. Power transistor-assisted Sen transformer (TAST) is a very recently introduced novel PFC that bridges the gap between most versatile flexible AC transmission systems controllers. It proved to possess closely comparable technical characteristics to that of the unified power flow controller (UPFC) at an installation cost that is less than the half. It is thus an attractive substitute of the UPFC for many utility applications. Nonetheless, since the TAST is a newly introduced PFC, it is of great importance to develop its steady-state model for its implementation in modern power systems analysis. The main contribution of this study is presenting two accurate steady-state models of the TAST: a simplified Simulink model (SSM) and a comprehensive Newton-Raphson model (CNRM) for its representation in the load flow analysis. The presented SSM and CNRM of the TAST are novel. A standard five-bus system and a modified IEEE-30 bus power system are used for demonstration of the effectiveness and validation of the SSM and the CNRM. Very closely comparable results are obtained when a TAST or more is used to increase and decrease the power flow in transmission lines.