Investigations into the upgrading of existing transmission lines from HVAC to HVDC

In general, HVAC transmission lines have an inherent design inefficiency whereby the conductor current carrying capability remains largely unused. With increasing system voltages and the consequential increase in conductor bundles; this design inefficiency worsens. When the same transmission line is converted to carry direct current, the full conductor current carrying capability can be fully employed. The net result is much higher power transfers, more economic utilization of existing assets and the removal of the need for new power line routes, rights of way and servitudes. HVDC also introduces many key technical and economic benefits such as lower power losses for bulk power transfers, creation of asynchronous power systems, advanced controllability of large power systems having both speed of response and intelligence of control. The paper presents the results of investigations into the power transfer constraints of and the benefits of converting HVAC transmission lines for higher power transfers under HVDC application.