News Release

In the “Fukushima Floating Offshore Wind Farm Demonstration project” by Ministry of Economy, Trade and Industry, Furukawa Electric and VISCAS Corporation successfully developed and manufactured the special-high voltage riser cable which electrically connects, under the sea, a 2MW floating offshore wind turbine equipment (power generation equipment) and an offshore substation (substation equipment). And Shimizu Corporation successfully installed the cables in the actual sea.
The special-high voltage riser cable is a power cable which floats in the sea and dynamically follows the movements of the floating equipments, the wave and the tide. There is no other example, in the world, of development and manufacturing of this kind of cable and its installation in the actual sea.

Furukawa Electric and Shimizu Corporation are members of the Fukushima Offshore Wind Consortium consisting of 10 companies and a university, entrusted with the “Fukushima Floating Offshore Wind Farm Demonstration Project” from the Ministry of Economy, Trade and Industry. In the experimental study, Furukawa Electric is responsible for the overall development of the power transmission system for the floating offshore wind farm and VISCAS Corporation is responsible for the manufacturing and the jointing of the special-high voltage riser cable. Shimizu Corporation, as a joint venture with Nippon Steel & Sumikin Engineering Co., Ltd, is responsible for the towing and the anchoring of the floating offshore wind turbine equipment from Naraha to a sea area a distance of about 20km, the laying and the burying of a submarine cable which connects Naraha and the anchoring sea area and the connection of the power generation equipment and the substation equipment with the riser cables.

The special-high voltage riser cables, installed for this time, consist of two kinds of cables. One is a 66kV cable (0.9km × one cable) which connects the substation equipment and the submarine cable drawn from Naraha, the other is 2.2kV cable (2.3 km × one cable) which connects the power generation equipment and the substation equipment. Outside diameter and weight are 146mm, approx. 42kg/m for 22kv cable and 175mm, approx. 52kg/m for 66kv cable. These cables have an excellent water tight performance, which prevents seawater penetration which used to be considered a weak point, and a fatigue resistance performance even for long term usage. To both riser cables, buoys are attached at the midpoint from the floating equipments and the bottom of the sea, and installed to draw the S-shape in the sea. S-shaped part is an adjusting extra length to follow the movements and the ups and downs of the floating equipments. Behavior analysis technology of Furukawa Electric played an invaluable role.

Meanwhile, the installation of the special-high voltage riser cable in the actual sea area is a construction with a high degree of difficulty because of the influence of waves and tides. Shimizu Corporation overcome the challenges in the construction, that is the shape in sea water (S-shaped) management, the cable length adjustment to maintain the shape and the cable end and the floating equipment joint work etc., by taking advantage of its high level of technology for marine construction developed in the construction of the deep-ocean water intake facilities and others.

Currently, at the anchoring area, the riser cable central portion burying construction to connect the power generation equipment and the substation equipment is in the final stage, and the construction is expected to be completed in a couple of days.