Floating wind turbines to power North Sea Gullfaks, Snorre platforms

Norway’s government has been pushing hard for `cleaner’ power to cut emissions from the country’s offshore field centers. Various operators have responded, with more schemes being tabled to import electricity directly from the shore through subsea power cables. Most of the projects either completed or in progress are for fields in the North Sea: the scope is becoming increasingly ambitious, with the Utsira High Power Grid set to bring power from the mainland to five field centers in the central Norwegian North Sea.

However, there are technical constraints such as distance from the shore and potential stresses on Norway’s grid with so many competing projects. For the Gullfaks and Snorre field complexes in Tampen area of the northern North Sea, Equinor and its partners have chosen an alternative approach, commissioning the world’s first floating offshore wind park designed specifically for powering oil and gas platforms. The 11 Siemens Gamesa wind turbines, supported by concrete hulls constructed by Aker Solutions, will be moored at a location 140 km (87 mi) offshore where winds are reliably stronger, in between the two field centers, in water depths of up to 300 m (984 ft). The turbines will collectively supply 88 MW of power to the five platforms, representing around 35% of the two fields’ needs.

This will offset some of the power currently provided by the platforms’ gas turbines. Use of these turbines will be scaled back, cutting annual CO2 emissions from the two fields by around 200,000 metric tons (220,462 tons), and nitrogen-oxide emissions by 1,000 metric tons (1,102 tons). Another factor driving the investment decision, taken in late 2019, was the need to secure government approval for extending production from Gullfaks out to 2036 and from Snorre to 2040 - up to 20 years more than planned in the original development submissions.

The 11 Siemens Gamesa 8.0-167 DD wind turbines, built in Cuxhavn, Germany, will feature a larger rotor, 167 m (548 ft) in diameter, with new aerodynamic 81.4-m (267-ft) long, fiberglass-reinforce epoxy blades providing a swept area of 21,900 sq m (235,730 sq ft) and pitch-regulated, variable-speed power. Another feature is the High Wind Ride Through (HWRT) system. When the wind speed is above 25 m/s (82 ft/s), wind turbines will typically shut down for self-protection. With the HWRT, however, the turbines slowly ramp down output power, leading to a smoother production rampdown and therefore a more reliable electrical grid.

Each of the floating wind turbines will be held in place by three mooring lines, connected to the seafloor via suction anchors. Under a joint venture, Aker Solutions and DOF Subsea are due to complete all assembly/offshore installations by summer 2022. JDR Cable Systems is responsible for design and manufacture of the 66-kV dynamic inter-array cables and the static and export cables (including breakaway systems) between the wind park and the two field centers. For Hywind Tampen, one of the main anticipated challenges is the dynamic stresses the cables will need to withstand in the Tampen area.

The 2.5-km (1.55-mi) long dynamic array cables will connect to the 11 turbines in a loop, while the two static 12-9 km (8-mi) and 16-km (9.9-mi) export cables will link the loop to the Snorre A and Gullfaks A platforms. JDR is manufacturing the cables and accessories at its plant in Hartlepool, northeast England, while parent company TFKable makes the cables’ power cores in Bydgoszcz, Poland.

Wood is responsible for integration of the wind turbines to the platforms and for the onshore control room in Bergen. The work scope includes design, integration and delivery of Employer SCADA and telecommunications systems to be installed in the wind turbines, and modifications to the power management system on Snorre and Gullfaks to ensure an optimized design using the wind power. Wood is also managing required topside modifications on the Snorre and Gullfaks platforms and the onshore control room, performing engineering, procurement, fabrication and installation.

According to Bjørn Kingestad, senior project manager at Wood, “the existing power management system (PMS) functionality on Snorre and Gullfaks will be upgraded to receive power from the wind farm. Electrical power system studies are being conducted to ensure that the electrical grid on Snorre and Gullfaks can integrate the new power source from Hywind Tampen. The work includes investigating dynamic challenges regarding power flow and capability when starting, running and disconnecting large electrical consumers and generators.

“The most central function for the PMS is to ensure a safe and predictable operation of the hybrid power system, capable of receiving both wind and gas turbine-generated power. The PMS will also ensure maximized use of wind power to minimized fuel gas usage and CO2 emissions. The introduction of wind power will not have a negative impact on the reliability/regularity of power supply on the platforms. If the wind park needs to be shut down, due, for instance, to an extreme weather event, power could be maintained on the platforms via the existing gas turbines which act as a back-up power source.”

The floating wind turbines will be connected to both Gullfaks and Snorre in a ring solution. Normally, five floating wind turbines will be connected to Gullfaks, and six to Snorre. The design will also accommodate other set-ups. “Structural changes are mainly related to the topsides modifications on Snorre A and Gullfaks A. As for the existing control rooms, the main tasks are modifying and creating new Human Machine Interface (HMI) operator displays used for supervision and operation of the system from the control room screens. Vysus Group (formerly Lloyd’s Register Energy) is supporting Wood with the Human Factors (HF) scope, while Goodtech is supplying the Employer SCADA system.”

Wood has performed Human Factors analysis and staged workshops, he added, to provide input to the modification and new HMI layout and graphics display design, including a new alarm/signal feature, and the layout design of the wind farm control room. The company is managing the engineering/design work from its offices in Stavanger, Bergen and Sandefjord, where necessary, using resources from other parts of the group.

“Over the past year the team has spent much time working from home due to COVID-19 restrictions,” he explained. “As both the Wood and Equinor project teams are split between different locations, working from home and co-operation via digital platforms has been working beyond expectations. We have had the same experience with our interfacing contractors on the Hywind Tampen project, these being split between different locations in Europe. However, our team has made site visits and plans more visits to the platforms and to the onshore control room, as permitted by safety and travel restrictions.”

Vysus Group, is also working directly with Equinor on interface requirements for staff at the onshore control room at Bergen, which will be located alongside an existing control room serving the normally unmanned Valemon platform. Although control set-ups for offshore wind farms are well known, this is the first instance of a wind farm powering offshore platforms. The Human Factors team is focused on conducting systematic assessments to support the development of knowledge necessary and relevant for designing and operating complex control room philosophies, based on multidisciplinary knowledge and multi project experience.

According to Mats Wang, Human Factors Consultant at Vysus group, “it’s important to get the right balance between automation and human interactions in the systems, and to ensure that the control room operators have the information that they really need and not too much or too little. The human factors analysis takes into account the new tasks and functions required and the risks associated with the level of automation built into Hywind Tampen.”

Maria Borén, Human Factors Specialist at Vysus Group, added: “Equinor has developed a system that takes different information from various sources, analyses this and gives advice on when to stop or start a gas turbine generator on the platform, in order to help the operators make decisions. They have experience from other offshore wind farms such as Hywind Scotland, so they can see what will be useful in terms of wind power production. With Hywind Tampen, the onshore control room will be the main control room, but there are also four other control rooms at Snorre A and B and Gullfaks A and C, and the staff there have to ensure they have enough power to run their platforms.

“During the design of the onshore control room we incorporate our experience from previous designs for offshore oil and gas installations and other projects. The onshore control room will have multi-field control of both the wind park and the Valemon installation and we need to consider what the Valemon operators are used to seeing and operating when designing for control of the wind park”

“For offshore wind farms there is a much higher level of automation compared with oil and gas. If something does go wrong in Hywind Tampen’s case, the system will either shut down or the Siemens Gamesa turbines will go into safe mode. But we are also looking to design the system so that control room operators can trouble shoot if something does fail. This involves going through various risk scenarios.

“Snorre is currently undergoing several projects, so their operators are used to ever-changing situations. But we are nevertheless thinking about the impact on the operators of the information we add to the control system, to prevent overloading the operators with information. The same applies to Gullfaks, which also has several ongoing projects. As there will be several platforms connected to the wind farm, the staff in the control rooms need to have the full picture. If, for instance, there are changes on Snorre A, these will also affect Snorre B."