DEVELOPMENT AND CONSTRUCTION
OF FLOATING SUBSTATION
Haruki Yoshimoto, Yuji Awashima and Yuka Kitakoji
Japan Marine United Corporation, Tokyo, 108-0014 Japan

Japan Marine United Corporation has developed, designed and constructed the world’s first floating substation forwind farm off the coast of Fukushima. To meet the requirements of the floating substation, e.g. reduced vessel motions,sufficient stability, etc., we have applied several unique technologies such as the advanced spar concept. And, in 2013
summer, we installed floating substation at off the coast of Fukushima. In this paper, we describe about the concept andcharacteristic features of floating substation. During the construction, we applied newly and unique method to construct(e.g. mega block erection, suspended dock out) because of the unique floaters shape. These methods are also describedin this paper.
Keywords: substation, wind power, offshore wind, offshore structure

INTRODUCTION
GeneralIn recent years, a social demand for introduction ofrenewable energy is increasing because of risingconventional fossil energy resource and the nuclear
power plant accident. For example, in the study ofpotential for renewable energy introduction published by
Ministry of the Environment [1], Japan’s potential for
introduction of renewable energy is estimated at morethan 2 million MW. Among them, the potential for windenergy is about 1.9 million MW and it is over 10 times thepotential for introduction of the other renewable energy
sources. Furthermore, wind energy can be divided inonshore and offshore, the potential for introduction ofoffshore wind energy is estimated at about 1.6 million MW.
In other words, 80% of the potential for introduction ofrenewable energy in Japan are occupied by offshore windenergy.

In Fukushima FORWARD, JMU is in charge of EPCI(Engineering, Procurement, Construction and Installation)of floater part of the floating substation. The floatingsubstation has been installed in fiscal 2013 summer.
In this paper, we describe characteristic features offloating substation. Then, we describe the unique method
to construct and install the floating substation.

Fukushima FORWARD
For the reconstruction of Fukushima Prefecture
severely hit by the Great East Japan Earthquake and theFukushima nuclear power plant accident at 2011, thegovernment of Japan started the experimental research
project of the world’s first floating offshore wind farm. This
project named as “Fukushima FORWARD (Fukushima
Floating Offshore Wind Farm Demonstration Project)” isconducted by the consortium made up of Marubeni
Corporation (project integrator), the University of Tokyo(technical advisor), Mitsubishi Corporation, Mitsubishi
Heavy Industries, Ltd, Japan Marine United Corporation,
Mitsui Engineering & Shipbuilding Co., Ltd, Nippon Steel& Sumitomo Metal Corporation, Hitachi, Ltd., Furukawa
Electric Co., Ltd., Shimizu Corporation and Mizuho
Information & Research Institute. And, this project has
been sponsored by the Ministry of Economy, Trade andIndustry since March 2012.

Fig. 1. Overview of Fukushima FORWARD

FLOATING SUBSTATION OF FUKUSHIMA FORWARD
The floating substation is a float designed to raise thevoltage of the electricity generated by the offshore windturbine and transmit the electricity to land. It is the world's
first challenge to construct floating offshore electric power
substation. Also equipped with instrument to observe
meteorological phenomena, oceanographic phenomena,and float motion of the targeted ocean area, it alsofunctions as an observatory obtaining data necessary foroffshore wind farm.

In the electrical substation equipment part, a 25MVA
transformer which raises the pressure of the 22kV
electricity generated by the wind turbine to 66kV isinstalled. Hitachi Ltd. is responsible for the electricalsubstation equipment.
Moreover, underwater transmission lines are used forelectrical transmission, connecting three 22kV lines andone 66kV line. Furukawa Electric Co., Ltd. is in charge ofthe transmission lines.

The electrical substation equipment is located insidethe upper hull which is at the top of the hull, a tower for
observing wind conditions and helicopter deck for accessin case of an emergency is provided. Also assuming an
operation in time of a power failure, it is equipped with an
auxiliary generator. The major equipments to be installed
are listed below.

Principal particulars and main components of floatingsubstation

・・・・

At first, we show the outline isometric view of thefloating substation in Fig. 2. And, principal particulars areshown in Table 1.

・・・

25 MVA Transformer
Electric Rise Cable
Observation Tower
Observation Instruments (Doppler Rider, 3D
Ultrasonic Anemometer, RTK-GPS etc.)
Helideck
Ballast PumpAxially Generator

The station keeping will be done with four mooringlines. The lines are composed by chains only and thenominal diameter is 132mm.
Design conditions
The location where Fukushima FORWARD will be
conducted is a sea area 20km offshore from Fukushima
Prefecture where the depth of water is approximately
100-120m. The yearly average wind speed in the sea
area is more than 7.5m/s at 100m above water. Tab. 2shows the setting of meteorological and oceanographic
conditions with 50 years return period.
In designing of the floating substation, Class NK Part
P and some Code and Regulations (COLREG andMARPOL, etc.) were applied. Note, however that there
are no crews, the classification society made significant
allowances for the life saving and firefighting criteria.
The floating substation needs to satisfy the stability
performance and low motion performance required by theelectrical substation equipment and observationequipment that will be installed. So we adopt “Advanced
Spar Concept” which had been developed by JMU from2009 [2].

Fig. 2. Isometric view of floating substation
Table 1.Principal particulars of floating substation
ItemValueLength (at middle hull)
33.4 mBreadth (at middle hull)
33.4 mHeight (base line to tower top)
Abt. 110m
Draft (Operating)50.0 mDraft (Maintenance)
32.0 m
Displacement
Abt. 13,000 ton

Also, as the riser cable has a limited range that it canfollow, in the same way as rigs connected with drillingrisers and offshore structures for production connectedwith flexible risers, there is a need to design mooring lines
so as it will not be pushed outside of the certain range byenvironmental external force.
Table 2.Design conditions for Fukushima FORWARD(Return period = 50 years)
Wind Velocity (10min, @10m)
41.8 m/s
Significant Wave Height
11.7 mSignificant Wave Period
13.0 sCurrent Velocity
1.5 m/s
Water Depth
100 - 120 m

CONSTRUCTION AND INSTALLATION
We show the construction and installation flow
diagram for the floating substation in Fig. 3. In this section,
we describe about the method to construct and install.
Part 4Construction
Anchor Installation&Mooring Line Laying

Suspended
Dock Out

Holding Power TestTowing

Upper HullPart 3COBMooring Line Connection
Part 2Riser Cable Connection

Middle Hull

Grid Connection&Final Commissioning

Start of Operation

Fig. 3. Construction and installation flow diagram.

Part 1

Lower HullFig. 4. Block division of floating substation.

Construction and dock out
The floating substation was constructed at JMU
Yokohama Shipyard Isogo Works from December 2012 toJuly 2013. To begin with, the upper hull, the COB hull, themiddle hull and the lower hull were separately constructed,and were constructed by composing the hull in order. The
block division is shown in Fig.4. At last, “Mega block”
composed by upper hull, COB hull and middle hull wasinstalled on the lower hull part (Part1 in Fig. 4). The
installation of mega block is shown in Fig.5.
After the erection, composed float was launchedtoward the installation site. Because the towing draft(32m) is deeper than the depth of dock (abt. 8m), the float
was lifted and suspended by the floating crane and towed
away from the dock (Fig. 6).
Installation
Before the towing of the float, mooring lines andanchors were installed beforehand and a test to see its
holding power was conducted. The holding power test
was conducted by pulling together the mooring lines onthe opposite side on the barge. Fig. 7 shows thedeployment of the high holding drag embedded anchor.
Fig. 5. Mega block installation on lower hull part.

Fig. 6. Suspended dock out.
The towing, with the condition of towing draft (32m),
was towed from Tokyo Bay going through Uraga Channel
to the installation sea are in the offshore of Fukushima
taking two days. The towing was done by one main
tugboat and three assistant tugboats, navigating at thespeed of approximately 4 knots. At the end of July, thefloat was connected to the previously installed mooringlines (Fig. 8) and electric riser cables.
Fig. 9. Floating substation installed

Finally, the floating substation was installed at off thecoast of Fukushima and started the operation as theworld’s first floating substation (Fig. 9) in 2013 summer.
ACKNOWLEDGEMENTS
Ministry of Economy, Trade and Industry (METI) is
acknowledged for sponsoring of Fukushima FORWARD
project. Hitachi, Ltd. and Furukawa Electric Co. are
acknowledged for designing and construction of floating
substation.
Fig. 7. Deploying the anchor.

References[1] Ministry of the Environment, Study of potential forrenewable energy introduction, 2011.
[2] H. Yoshimoto et. al. , “Development of floating
offshore substation and wind turbine for Fukushima
FORWARD”, Proceedings of the International Symposiumon Marine and Offshore Renewable Energy, 2013.

Fig. 8. Installation of mooring lines