Power upgrading of Transmission Line by converting EHVAC into EHVDC

The increased demand for power transfer in combination with environmental and economic issues which set constraints to building new lines, force the implementation of new technologies into the existing system in order to improve its power capability. The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as HVDC, which can be applied to transmission and distribution systems. -Long extra high voltage (EHV) ac lines cannot be loaded to their thermal limits in order to keep sufficient margin against transient instability. With the scheme proposed in this paper, it is possible to load line conductors to their full current capacity. This paper gives the feasibility of converting a double circuit EHVAC line into EHV DC. Experimental studies are carried out for the determination of increase in percentage power. No alterations of conductors, insulator strings, and towers of the original line are needed. Each HVAC circuit uses 3 conductors but HVDC uses only 2, so the two circuits (6 conductors) that are often used for HVAC transmission may be converted into three HVDC circuits , each with 2 conductors. This change can increase transmission capacity of a double-circuit HVAC line by a factor of 3 or more.