Enhancement of Power transmission capacity of existing ac transmission lines by refurbishing to HVDC transmission

The ever increasing demand for electricity augmented with industrialization and economy growth in developing countries like India has motivated the integration of new generating sources both conventional and Renewable Energy Sources (RES). Over a period of time, this has led to transmission congestion on the existing AC transmission lines. With integration of various RES distributed along the transmission sections, their power evacuation is being challenged with the existing transmission capacity infrastructure. The generation from RES is also intermittent that transmission system cannot be planned for its peak generation for economic reasons. Construction of new transmission lines is becoming difficult due to non-availability of right of way (RoW). Owing to these reasons, it has forced the system planners and Transmission system operators (TSO) to look for alternative technologies for enhancing the power transmission, integration of distributed RES, optimal use of existing right of way, etc. which has become a subject matter of interest at the current scenario. One such alternative technology is the use of High Voltage Direct Current (HVDC) transmission, which has many advantages like enhanced transmission capacity up to thermal limit, low losses, ease of controllability, less RoW, etc. Especially voltage sourced converters (VSC) based HVDC technology is capable of independent control of real and reactive power, voltage support to the connected ac system, black-start capability and better reliability. Thus conversion of existing AC transmission infrastructure into HVDC transmission is taken as the study case to understand the challenges and opportunities during such refurbishment.