AORC Technical meeting 2014

Transcription

1 http : // B AORC Technical meeting 2014 Dynamic Installation for Fukushima Floating Offshore Wind Farm Demonstration Project Yasuhiro Tominaga, Hiroshi Nakano, Koji Tomikuda, Masayoshi Toyoda Shiro Torii, Kiyotomo Yagihashi, Masahiro Minamide, Yuji Tateno VISCAS Corporation Japan SUMMARY Furukawa Electric Company (FEC) and VISCAS Corporation have proceeded with a Fukushima FORWARD Project (FF project) as one of the commissioning manufacturers of the Ministry of Economy, Trade and Industry. The Ministry has a plan of a floating wind turbine development for a powerful choice of renewable energies in Japan. FEC and VISCAS are responsible of a transmission system and this paper reports the development condition of the power transmission system, mainly the development of a high voltage dynamic cable, which is considered as an essential technology. A behavior of dynamic cables subjected to under-water rolling caused by the steadily wave movement is different from that of the static submarine cables. Therefore, a development point is the improvement of a fatigue withstands property. For a practical application of riser cables, a target is to achieve the similar endurance life of a floating body or of a wind turbine. KEYWORDS Renewable Energy - Floating Wind Turbine - Power Transmission - Dynamic - - High Voltage yu-tateno@viscas.com

2 1. INTRODUCTION An offshore floating wind turbine is a promising power generation method in Japan, because Japan has the 6th largest exclusive economic zone (EEZ) in the world and has few suitable shallow shores for the implantation of the offshore type wind power generations. Offshore floating wind power generations are very few in the world. The construction of a wind farm possessing complex floating windmills with an offshore floating substation will be a first in the world. As the installation of dynamic cables, which is an essential technology for the offshore floating system, have been successfully completed, this paper reports the development condition of the project dynamic cable system and installation method. 2. OVERVIEW OF THE FF PROJECT 2.1 Project Overview The FF project consists of a 1st stage ( ) and a 2nd stage ( ). In the 1st stage, a 2MW down-wind type offshore floating wind turbine generator and a 25MVA offshore floating substation, for the first time in the world, have been constructed. In the 2nd stage, it is planned to construct two new 7MW floating wind turbine generation facilities and to install the riser cable toward an offshore substation. Figure 1 shows the project overview [1]. 2MW Windmill 7MW Windmill 66kV Riser 1st stage Substation 22kV Riser 7MW Windmill 22kV Riser 2nd stage Figure 1 Project overview 2.2 Transmission and Substation System The wind power generation capacities are 2MW and 7MW respectively. A 22kV cable (inter-array cable) is selected for the transmission line towards the offshore substation. The route distance from the propose shore position to a windmill installing potential position is approx. 25km long with a submarine cable. In the FF project an offshore substation has been constructed to raise the cable (export cable) voltage up to 66kV for power transmission to the shore port because a 22kV cable has higher transmission loss. The export cable on shore has been connected with an already installed nearby 66kV overhead transmission line which is operated by a power utility, a transformer station installed on the way, and so a systematic grid link has been completed. Figure 2 illustrates the transmission and substation system [1]. 1

3 & Shore System Grid Transmission Line (66kV/22kV substation / observation tower) 22kV Windmill & Semi-submersible Floating Structure Intermediate Buoy 66kV Riser Intermediate Buoy Intermediate Buoy 22kV Riser Figure 2 Transmission and substation system 3. DEVELOPMENT OF THE RISER CABLE 3.1 Fundamental Design The authors have a lot of experiences in submarine cables, submarine oil pipes, deep-sea water suction pipes etc., and wealth of investigation experiences in dynamic applications. An analytic simulation technology is important for the dynamic application and an entire investigation of the submersible floating shape is required. Figure 3 illustrates the riser cable design flow. Start Wave condition & floating structure condition Riser parameter & fundamental property Decision on riser shape Redesign Static behavior analysis Floating structure static displacement absorption amount NG Floating structure response characteristics OK Dynamic behavior analysis Current wave statistic data Floating structure dynamic displacement absorption amount OK Fatigue analysis Durability satisfaction OK End NG fatigue data (SN characteristics) NG Figure 3 Design flow of riser cable 2

4 A fixed wave condition and a floating body s rolling condition are needed at first for external conditions. A static behavior analysis, a dynamic behavior analysis and a fatigue analysis are in turn conducted with combinations of the various parameters and the shapes for a riser cable under above conditions. The analysis and feedbacks are reiterated and finally the most suitable submersible shape design and its detailed riser cable design are defined. The riser cable required in the FF project is different from the past experienced 6.6 kv cables, with respect to its application to a 22 kv and to a 66 kv voltage cables, because their cable outer diameters and weights become larger and their electrical stress are more severe. The riser cable is therefore required for the power cable construction to provide a superior fatigue withstand characteristic. It is essential for a conceptual construction of the submarine cable to meet the specification in accordance with the electrical equipment technical standards and for its electrical and mechanical characteristics to satisfy JEC-3408 [2], CIGRE TB 490 [3] and CIGRE Electra No.171 [4]. The requirements of the riser cable characteristics for dynamic cables are shown in table 1. Table 1 Target characteristics Item Target characteristics Sea condition at - Meet allowable tension and minimum installation site bending radius in floating condition Floating structure - Floating part of the cable should not rolling condition touch the sea bed - should not be kinked Fatigue life design - Similar to windmill or floating structure Based on the previous findings, the riser cable construction is defined as shown in figure 4. The cable has double layers of strand armor wires twisted in opposite directions in order to prevent cable torsion. Conductor Conductor screen XLPE Insulation Insulation screen Metallic screen Metallic Sheath Inner jacket (PE) Filler Bedding Armor Outer jacket (PE) Optical fiber unit Conductor 3 x 100 mm 2 XLPE Insulation 11 mm Inner PE jacket 3.5 mm Armour Outer PE jacket Outer diameter Weight Galvanized steel wire (6.0 mm) 6 mm 175 mm 53 kg/m in air Figure 4 Structure of 66 kv riser cable 3

5 3.2 Installation The transmission system was installed in order of submarine cable, riser cable and submarine joint. The 66kV riser cable was installed form the substation to the jointing point with submarine cable. After installing the riser cable, the submarine joint was constructed on the vessel with the submarine cable which had been installed. The installation procedure of 66kV transmission line cables is illustrated in Figure 5. The installation of riser cable and submarine joint is shown in figure 6 and figure 7. 66kV Riser Submarine cable installation Submarine joint construction on vessel 66kV Riser 66kV Riser Riser cable installation Submarine joint installation 66kV Riser Pulling up both cables to vessel Figure 5 Installation procedure of 66kv transmission line cables 4

6 Figure 6 Installation of riser cable Figure 7 Installation of submarine joint 4. CONCLUSION The 1st stage of the FF project was successfully completed in 2013 and it is already under operation. The further development is undergoing at 2nd stage This research is carried out as a part of Fukushima floating offshore wind farm demonstration project funded by the Ministry of Economy, Trade and Industry. The authors wish to express their deepest gratitude to the concerned parties for their assistance during this study. References [1] Fukushima Offshore Wind Farm Consortium [2] JEC-3408 High voltage testing method for Special high voltage cross-linked polyethylene cable and its splice for kv, 1997 [3] CIGRE TB 490 (Recommendations for Testing of Long AC Submarine s with Extruded Insulation for System Voltage above 30(36) to 500(550) kv) [4] CIGRE Electra No.171 (Recommendations for Mechanical Test on Sub-marine ) 5