POWER UPGRADING OF TRANSMISSION LINE BY SIMULTANEOUS AC-DC TRANSMISSION

POWER UPGRADING OF TRANSMISSION LINE BY SIMULTANEOUS AC-DC TRANSMISSION

Due to restrictions imposed on new transmission lines because of right-of-way cost, environmental and regulatory concerns. There is a need to enhance the power transfer capability of the existing lines without major changes. This paper gives the feasibility of enhanced power transfer by simultaneous ac-dc transmission through the same line. According to the characteristics of long extra high voltage (EHV) ac lines cannot be loaded to their thermal limits in order to keep sufficient margin against transient instability. With scheme proposed in this paper, it is possible to load this line very close to their thermal limits. The conductors are allowed to carry usual ac along with dc superimposed on it. The added dc power flow does not cause any transient instability. This paper gives of converting a double circuit ac line into composite ac-dc power transmission line to get advantages of parallel ac-dc transmission to improve stability and damping out oscillation. Simulation and experimental studies are carried out for the coordinated control as well as independent control of ac and dc power transmissions. No alterations of conductors, insulator strings and towers of the original lines are needed. Substantial gain in load ability of the line is obtained. This thesis presents the method to convert an existing double circuit EHVAC line into simultaneous ac-dc transmission line simulation is carried out using MATLAB SIMULINK.

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