New Hokkaido-Honshu

The New Hokkaido-Honshu HVDC Link is a high-voltage direct current transmission system connecting Hokkaido and Honshu, the main island of Japan. This project was designed to enhance power interchange capabilities and strengthen the resilience of the transmission network between the two regions.

Technical Specifications

The New Hokkaido-Honshu HVDC Link has a rated power of 300 MW ± 100 Mvar, with a rated voltage of 250 kVdc and a rated current of 1200 Adc. It employs an voltage-sourced converter (VSC) MMC HVDC system, which is the first of its kind in Japan.

The link consists of two converter stations: the Hokuto converter station in Hokkaido and the Imabetsu converter station in Aomori, Honshu. These stations are connected by a 122-kilometer-long hybrid DC transmission line. The stations include VSC converter valves, converter transformers, AC and DC gas-insulated switchgear (GIS), and control and protection systems.

Cable System

Sumitomo Electric Industries supplied and installed the cable system for this project. The system uses 250-kV DC XLPE (cross-linked polyethylene) cables. Approximately 24 km of these cables were installed inside the Seikan Tunnel, making it the longest HVDC cable system in the world for a strait tunnel.

The cable route consists of 24 km in the subsea tunnel and 98 km outside the tunnel, for a total length of 122 km. Sumitomo Electric also supplied 98 km of overhead conductors and provided technical support for the overall transmission line installation.

System Capabilities

The VSC HVDC system offers several advantages over the traditional line-commutated converter (LCC) HVDC systems used in Japan prviously. It enables black-start operations, allowing power transmission from Honshu to Hokkaido during blackout situations in Hokkaido. Additionally, it can control reactive power output independently from active power transmission.

The system does not require harmonic filters or reactive power plants, which are typically necessary for LCC HVDC systems.

Power Electronics

The power switching device used in this system is the Injection Enhanced Gate Transistor (IEGT), manufactured by Toshiba Electronic Devices & Storage Corporation.

Project Timeline and Impact

Construction of the New Hokkaido-Honshu HVDC Link began in August 2016, and commercial operation started on March 28, 2019. The completion of this project increased the total transmission capacity between Hokkaido and Honshu from 600 MW to 900 MW.

Future Developments

As of December 2024, plans are underway for further expansion of the New Hokkaido-Honshu interconnection, by adding a second pole. This will convert the asymmetric monopole configuration to a bipole, and double the power transfer capacity. Further, Japan Interconnector Inc. and Frontier Power Ltd. have submitted a pre-qualification expression of interest for a new 2 GW HVDC 800km submarine power cable project between Hokkaido and Honshu along the Japan Sea route.