Power trip

Elaine Maslin

August 1, 2016

Subsea power remains on the agenda for the subsea processing systems of the future. Elaine Maslin surveys the main players’ progress in producing subsea power distribution systems.

The subsea factory – as envisioned by ABB. Images from ABB.

The future of subsea processing systems based on long-distance step-outs has long been seen as a challenge.

For projects requiring power for pumps, booster stations or even compressors, etc., power has to be supplied from somewhere at a cost that doesn’t inhibit the economics of the project.

Subsea power distribution, through a system able to deliver power to multiple users – pumps, compressors etc. – via one power cable to the subsea system, instead of needing separate cables to each user, has been seen as an enabling technology. It could help to increase step-out distances and reduce costs for medium-long distance tiebacks, as well as reduce topside space requirements.

The challenge has been to make subsea power electronics, controls, drives, etc., work in the subsea environment, up to 3000m deep. This includes switchgear, variable speed drives and controls, and auxiliary equipment. Switchgear systems enable many loads on one cable, for power distribution. The variable speed drives enable the pumps and compressors to vary their speeds—this is the biggest and most complex component—and the controls enable remote control and monitoring. The auxiliary equipment covers components such as power to magnetic bearings, instrumentation, etc.

While subsea pumping, boosting and now compression (with a record 43km-long 18MVA, 120Hz step out at Åsgard), have been achieved, the rollout has been limited, in terms of the number of projects. To date, they have also relied on being connected to a topside’s variable speed drives and switchgear. So far, only transformers and motors have been placed on the seafloor.

“Oil companies see the potential for subsea boosting and pumping, but they see the electric power system as one of the main costs, due to the cable costs,” says Asmund Maland, alliance manager, ABB, on the ABB/Aker Solutions alliance, formed earlier this year. “If you can make a smarter solution, more projects will be realized.”

“Building platforms and shipping people back and forth is very expensive,” adds Jan Bugge, vice president and project manager of ABB and Statoil’s subsea power joint industry project (JIP). “By putting equipment on the seabed you can use less power, because you are closer to the reservoir, and reduce operational costs. That’s why this is important.”

ABB’s subsea power distribution station, an artist’s impression. 

Qualified

GE Oil & Gas has a qualified system, after years of work on component, sub-assembly and full system testing for Shell’s Ormen Lange subsea compression project. The system would transmit power from shore some 120km to Ormen Lange. GE says the system is based on known and understood surface components, which have been marinized in one-atmosphere containers to be used on the seafloor.

While the project it was meant for was put on hold in 2014, GE Oil & Gas went through completion of the system, which successfully completed a 4000-hour testing regime late last year. This resulted in it being “the world’s first system test incorporating a subsea switchgear and subsea drives.”

Gilles Chene, senior sales manager, GE Power Conversion, outlined the project at the Underwater Technology Conference in Bergen in June. “For us, the project started in 2007. From 2009, testing started, followed by integration and, in 2011, submerged installation at Nyhamna pit [at Shell’s plant],” he said. Testing has been running from 2012 to late last year, he said, amounting to some 4000 hours, including a 72-hour full load test.

The system incorporated a 20MVA transformer, switch gear unit, with 35kV circuit breakers and control systems, variable speed drive (VSD), a 12.5MW, vertically installed compressor and 500kW pump, and other auxiliary systems. The full load test ran with 10,100 rpm motor speed.

“The objective was to ensure a high speed drive could be created subsea,” Chene says. “It exceeded expectations. The whole uninterruptable power system (UPS) proved reliable through the full campaign.”

An “ultimate test” saw the system’s fans switched off to test performance and this worked, Chene says. While the system was designed to operate without fans, using natural air circulation, it was seen that use of fans could prolong operational life.

A concern around subsea power supply from encased units has been the potentially limited information available as all elements are out of reach, Chene says. To mitigate this, a condition monitoring system was put on all units to provide measurements and run different data.

As qualified, the system could provide power to a hub, from which power could be distributed up to 20km out to 10 or more boosting stations, depending on power requirement, Chene says. “The final arrangement will be a tradeoff between size of modules, connectors, cable size and size of the units,” he says.

The aim now is to build on this technology to develop a far more compact system, looking at the different materials that have become available since the project started in 2007, as well as progress in power electronics, but also because this system was designed for use with a large compression project. “For us now it is about industrialization, not changing the technology,” says Kristin Elgsaas, senior product manager, GE Oil & Gas. “Changing the configuration so it is easier to assemble and reduce risk.”

On show

ABB also has a full system ready – in model form for show at least. The firm is working on a US$100 million JIP with Statoil, signed in 2013, to qualify a system able to transfer 100MW over up to 300km in up to 3000m water depth. Chevron and Total are also partners.

ABB will have a scaled 3D model of the system it is working towards qualification on at its stand during ONS in Stavanger this month [August].

Bugge says that the JIP is going well. ABB is putting its components in pressure balanced oil-filled containers, so that they can withstand the pressures at 3000m water depth without large, thick containers and make use of cooling mechanisms using the oil. “Reliability is key,” he says. These components need to live and operate reliably at 3000m water depth for years.

Currently, the large power and automation firm is working on qualifying components, including the power cells, which will form part of the variable speed drives. ABB will then start building the first prototypes this year. Full system testing, covering 3000-hour testing, is due in 2018. Market application is most likely after 2020.

“We are working on the building blocks, [such as] circuit breakers, which go into the switchgear, and then building the first prototype switchgear towards next year.  In the same way, we are building up components for the power cells for the subsea drives.”

Testing on the first drive will be done in Finland, where all the shallow water tests for the transformers have already been completed.

“The variable speed drive is complex,” Bugge says. “It is built from key power electronic components, power transistors, and has to be able to handle large power.” Indeed, there’s a lot of detail across the whole project. “And that’s what we are discussing with customers as we speak,” he says. “It’s hundreds and hundreds of tests.” Maland also highlights detailed work being done around software to enable the switchgear to provide a smooth power supply to users.

While investment appetite is low currently, due to the low oil price, there’s no reduced appetite for the work ABB is conducting on subsea power, Bugge says. “Oil companies are focusing on what’s closer [nearfield exploration and tiebacks],” he says of the current climate. “But, new technology is required and new technology will enable different ways to get resources out of the ground. The very long step-out is a natural step. In the depressed economy, the focus is on what’s near but it [long step-outs] will definitely come, and with it the need for new equipment at the seabed.”

Earlier this year, ABB and Aker Solutions formed an alliance that will see them pool forces in this area. “One of the key areas is subsea boosting as well as subsea compression project,” Maland says. “ABB and Aker have complimentary technologies. They cover hardware for subsea production equipment and ABB is mainly in the power space but also control and automation.”

On something like subsea compression, Aker Solutions would be and is looking to reduce the equipment footprint, while ABB will look at how electrification can be optimized so it’s ready for new projects.

Siemens

Siemens is also working on a subsea power distribution system, which it calls Siemens Subsea Power Grid (SPG), since 2010, alongside a joint industrial partnership program with selected oil majors.

The firm says all major design and engineering work is in its final phase and that its current focus is on final assembly and testing at its purpose-built Siemens Subsea Technology Centre in Trondheim, Norway.

Siemens’ subsea transformer was qualified with a full load shallow water test in 2012, and is currently being commercialized. Siemens’ subsea adjustable speed drive and subsea switchgear are being assembled and tested successfully. All main units will run through a system integration test in the factory in early 2017, with a plan to perform a full load system test in water during summer 2017.

“More than 80 engineers are currently working on this major development program, which has allowed Siemens to file for more than 120 patents,” says Patrick Brandmaier, head of Siemens Subsea Systems. “The substantial investment and competence build-up has allowed the launch of further programs successfully, with industrial partnerships in related areas of technology such as subsea power and subsea control.”

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