Nowadays, stable electricity supply is a formidable challenge. Bipolar submarine cables (total transmission capacity: 600 MW) are installed across the Tsugaru Strait between Hokkaido and Honshu islands in Japan. To make electricity supply more reliable in Hokkaido, Hokkaido Electric Power Co., Inc. has additionally planned the installation of a 300 MW interconnector, which is the Hokuto-Imabetsu DC Trunk Power Line connecting Hokuto Converter Station in Hokkaido with Imabetsu Converter Station in Honshu. Of the line length of 122 km, Sumitomo Electric won a contract for a 24 km underground power transmission cable installation in the Seikan Tunnel. The cable selected for this project was a 250 kV XLPE cable with excellent DC characteristics. This is the world’s longest ultra-high-voltage cable installation in a strait tunnel.

One major feature of this project is the installation work in a long undersea tunnel. The installation work will take place in the service tunnel provided along the main tunnel through which Shinkansen bulletin trains run. It is necessary to coordinate the work carefully with other contractors to avoid the duplication of operations, accidents, or trouble. Sharing this awareness among all those concerned, Sumitomo Electric is promoting the project in a concerted effort toward the commencement of service scheduled for March 2019.