The electrical needs in the Indonesian archipelago are often met through inter-island transmission, such as in Bangka Island, which has limited energy resources, necessitating a transmission from Sumatra Island via a submarine cable transmission line. This study aims to analyze the impact of changes in the phase conductor modification on a submarine cable transmission line on transmission capacity and the quality of interconnection between Sumatra and Bangka Island. The methodology used includes literature studies, secondary data collection from utilities and manufacturers, transmission parameter calculations, and analysis of results. The findings show that increasing the Geometric Mean Distance (GMD) or distance between phase conductors results in a significant increase in cable impedance, leading to a decrease in current carrying capacity and increased total power losses, with the maximum transmission capacity dropping from 80.64 MW to 40.91 MW. This change marks a challenge in meeting the energy demand in the system, especially during the off-peak load period. The results of this research are expected to form a basis for planning to anticipate potential similar disturbances in the future, enabling utilities and related parties to formulate more effective mitigation strategies and minimize the risk of system disturbances. © 2024 IEEE.