Transmission Expansion Planning with High Surge Impedance Loading Lines at Reduced Voltage Levels

Transmission expansion planning (TEP) addresses the intricate task of optimizing new transmission infrastructure within an existing grid to meet system objectives. As a critical strategy in power system development, TEP significantly influences the long-term efficiency, reliability, and scalability of the network, with enduring effects on overall system performance. This paper explores the application of unconventional high surge impedance loading (HSIL) lines as a cost-effective alternative to conventional extra high-voltage (EHV) transmission lines. By optimizing the geometry of subconductors, HSIL designs could achieve higher power delivery capacities while operating at reduced voltage levels, addressing the increased demand for sustainable energy infrastructure. Two 500 kV HSIL line configurations are analyzed for their feasibility in replacing the conventional 765 kV transmission lines for the TEP to integrate the large-scale wind energy sources located in far remote areas. The analysis is carried out within the 23-bus EHV test system. This study reveals that both HSIL line configurations successfully meet the technical constraints of the TEP problem, ensuring reliable system operation even under contingency conditions. Therefore, the HSIL lines offer significant cost savings due to infrastructure and accessories at reduced voltage levels with much smaller right of way (ROW) than conventional counterparts. This underscores the potential of unconventional HSIL lines to contribute to more sustainable and cost-effective grid planning strategies for integrating large-scale renewable energy sources.