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ENHANCEMENT OF LOADABILITY CRITERION OF TRANSMISSION & DISTRIBUTION LINES BY USING FUZZY LOGIC CONTROLLER WITH STATCOM

Due to the rapid technological progress, the consumption of electric energy increases continuously. But the transmission systems are not extended to the same extent because building of new lines is difficult for environmental as well as political reasons. Hence, the systems are driven closer to their limits resulting in congestions and critical situations endangering the system security. Power Flow Control devices such as Flexible AC Transmission Systems (FACTS) provide the opportunity to influence power flows and voltages and therefore to enhance system security, e.g. by resolving congestions and improving the voltage profile. Even though the focus lies on Static Var Compensators (SVC), Thyristor-Controlled Series Compensators (TCSC) and Thyristor-Controlled Phase Shifting Transformers (TCPST), the developed methods can also be applied to any arbitrary controllable devices. In order to benefit from these devices, an appropriate control is necessary. In this thesis, an Optimal Power Flow problem is formulated and solved to find the optimal device settings. Two types of FACTS devices, SVC and TCSC, can be installed on buses and transmission lines to enhance the transmission loadability (TL) of power systems, respectively through injecting reactive power and changing line reactance. In this paper, there are three main steps in the FACTS devices installation strategy proposed. In step 1, based on the peak-load state, the CPF technique is used to formulate the maximum transmission loadability (MTL) problem to maximize the TL increased from the peak-load through installation of the FACTS devices. Here, the MTL without FACTS device installed is first calculated. While in step 2, based on the power flow solution for the MTL obtained in step 1, the positions proper to place SVCs and TCSCs are determined using the tangent vector technique and real power flow performance index (PI) sensitivity factors, respectively. Various FACTS devices installation schemes are then built with these candidate positions and, for each scheme, the MTL is solved by determining the ratings for the SVCs and TCSCs installed. Finally in step 3, by comparing the ratios of the investment costs to the TLs increased between various schemes, a correspondingly most advantageous scheme is suggested. Also, to further validate the effectiveness of the proposed method, a static voltage stability analysis is given.