Shielding of Unconventional High Surge Impedance Loading Transmission Lines

ABSTRACT The ever‐increasing demand for electricity necessitates constant innovation in the electric utility sector. In this regard, high surge impedance loading (HSIL) transmission lines can be a promising technology. While conventional HSIL designs rely on more subconductors located symmetrically on circular bundles with a larger radius, unconventional HSIL lines can achieve even more natural power by optimally positioning subconductors in space. This paper focuses on determining the optimal location and number of shield wires for a newly designed 500 kV unconventional HSIL line, whose surge impedance is reduced to 141.5, resulting in a 74% increase in SIL compared to a conventional configuration (996 MW). New equations for calculating line inductance and capacitance, considering transposition for both phase and bundle arrangements, are developed. The shielding design aims to maintain an SFFOR of 0.05 flashovers per 100 km‐years. Numerical analysis indicates that placing the shield wire at = 7.2 m yields SFFOR = 0.047 under high lightning activity (Td = 30), while = 6.35 m maintains SFFOR < 0.05 under low activity (Td = 5). These results are validated through geometric circle diagrams, demonstrating effective shielding for all three phases without increasing tower height. This study presents a practical shielding method for unconventional HSIL lines that have the potential to revolutionize bulk power transmission.