Kii-Channel

The Kii Channel HVDC system is a submarine power cable system in Japan, connecting the Anan converter station on Shikoku island with the converter station at Kihoku on Honshu island. It once held the record as the world's highest-capacity HVDC submarine power cable system using a single bipole, with a rated power of 1400MW.

Technical Specifications

The system's first stage, commissioned in June 2000, operates at a bipolar voltage of 250 kilovolts (kV) and is rated to carry 1400 megawatts (MW). The project was designed with a planned second-stage upgrade to 500kV, which would increase the transmission capacity to 2800MW. However, this upgrade has not been implemented.

The converter configuration consists of 480 thyristors, with 40 in series per arm, 6 modules per arm, and 12 arms in total. The thyristor devices have a rating of 8kV/3.5kA and use 150mm (6 inch) Light-Triggered Thyristors (LTT). These thyristors, built by Hitachi, Toshiba, and Mitsubishi Electric, were the largest ever made at the time of installation.

Transmission Line

The transmission consists of two sections. The first 50 kilometers run north from the Anan converter station as an undersea cable. At Yura, there is a switching station, and from there the HVDC line continues for another 50 km as an overhead line.

Innovative Features

The Kii Channel HVDC system introduced several innovative features when it was built. It was the first HVDC project to use Gas-Insulated Switchgear (GIS) on the HVDC side. The system employs light-triggered thyristors, which offer performance and cost advantages by eliminating numerous components in the electronic firing unit. The HV cable, DC switchgear, and DC reactor were initially rated for the higher voltage of 500kV, anticipating the planned upgrade.

Purpose and Benefits

The primary purpose of the Kii Channel HVDC link is to connect two electric power systems in western Japan, stabilizing and reinforcing power systems in that region. It is used primarily to deliver large amounts of electric power from a coal-fired thermal power plant owned by EPDC and Shikoku to a plant owned by Kansai.

System Components

The HVDC station includes several key components. The AC filters are conventional, passive double-tuned and high-pass filters with internal fused capacitors and air-cored reactors. DC filters are passive type with either air or oil-cooled reactors. DC current transformers (DCCTs) are zero-flux type. DC Controls are mainly digital, with some analog parts for protection and firing units.

Performance and Reliability

The Kii Channel HVDC system was designed with specific reliability and availability targets. These include a Forced Energy Unavailability (FEU) of 0.5% or less, a Schedule Energy Unavailability (SEU) of 1.0% or less, a Single Pole Forced Outage Rate of 6 per year or less, and a Bipole Forced Outage Rate of 0.1 per year or less.