Japan’s Organisation for Cross-regional Coordination of Transmission Operators (OCCTO) has approved a wide-area grid development plan to enhance transmission capacity between Honshu and Kyushu through the Chugoku–Kyushu interconnection project.
The plan aligns with Japan’s seventh basic energy plan (2025) and builds on earlier grid expansion strategies from 2017 and 2021 to support large-scale renewable energy integration and improve system resilience in western Japan. The project will be jointly implemented by Chugoku Electric Power Transmission and Distribution Company, Kyushu Electric Power Transmission and Distribution Company, and J-Power Transmission. It features the construction of a 500 kV interconnection system comprising alternating current/direct current (AC/DC) converter stations on both ends, a 525 kV DC submarine cable of approximately 54 km, and overhead transmission lines spanning 26 km on the Honshu side and 4 km on the Kyushu side. Each converter station will be rated at around 1,000 MW/±300 MVAr, operating initially in monopole mode with provisions for future expansion to a 2 GW bipolar configuration. The project also includes switching stations, phase modifiers, and system stabilisation equipment to ensure voltage control and operational reliability.