What happens when a transformer is placed 3000 meters under water?

Transformers are one of the components that must be fitted so that they are able to stay on the sea bed for decades

A subsea transformer must not only be robust enough to withstand the pressure from the water, but must also be able to do the job flawlessly year after year

A subsea transformer must not only be robust enough to withstand the pressure from the water, but must also be able to do the job practically without maintenance year after year. It’s a requirement that also applies generally to underwater equipment.

Electricity would have been almost unthinkable without transformers. Transformers are used to increase the voltage to transfer power efficiently. Or to lower the voltage when power is transmitted over long distances, making it useable at the other end.

What does it take for a transformer to operate at depths of several thousand meters?

ABB provides two main types of subsea transformers, containing either a single or double shell box. The transformer is filled with liquid and uses pressure compensation to ensure the internal pressure equals the pressure of the water on the outside. This prevents the transformer shell from collapsing. The necessary cooling is provided by the low temperature of the sea.

ABB was the first supplier of subsea transformers and is still the largest provider of subsea transformers in the world. The first of some 20 subsea transformers were delivered in 1998. All of them have performed successfully during this time. Subsea transformers from ABB are already frequently used in connection with pumps, compressors, pipe heating, distribution and conversion. However, the transformers must withstand increasingly tougher requirements.

A few years ago we conducted successful testing of the world’s largest subsea transformer that is built for depths of up to 1,000 meters. The technology will soon be used for subsea gas compression at the Ormen Lange field on the Norwegian Continental Shelf.

ABB has qualified a transformer that is rugged enough to operate 2,500 meters below the surface. Transformers that can be placed as low as 3000 meters are just around the corner, and this is part of our ongoing development program. Our subsea transformers are manufactured in Vaasa in Finland, and this technology will be the subject of a study by a Joint Industry Program (JIP) that was signed between Statoil and several other oil companies last year – with ABB as the technology provider.

Today, a typical system for electrical transmission of power to a motor on the seabed consists of a transformer and an inverter on the platform, as well as submarine cable and a transformer on the seabed.

The distance from a variable speed drive on the platform to the electrical transmission system will affect how it behaves in an electrical sense. Some of the challenges are harmonic distortion and voltage drop, which may cause failure of electrical equipment on the seabed.

Both transformers and inverters are tailored for each project and are not available off the shelf yet. But when the subsea factories are more common, the need for industry standards will emerge.

The world’s leading oil and gas companies share this vision of a complete subsea factory. The challenge is that these underwater facilities may have a power consumption equivalent to that of a small city. Putting transformers on the bottom of the sea is just part of the puzzle and one where we’re excited to have taken a pioneering position.

Subsea transformer testing in Vaasa, FInland.
Photo showing testing of a transformer in Vaasa, Finland as part of the qualification of technology in connection with underwater gas compression on Ormen Lange. Foto: Johannes Tervo/ABB

Interested in reading more?…Try Twenty thousand leagues under the sea – 2020 version




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About the author

Tor-Eivind Moen

I lead sales and technology development for subsea power supply and power from shore in ABB's oil and gas business. Earlier my experience included sales and development of electrical systems and power electronics related to renewable energy. I have been at ABB since 1991. I worked for ABB in Switzerland and in the United States before I came to ABB in Norway in 2005. I graduated from the Norwegian Institute of Technology and have an Executive MBA from the University of Wisconsin in Madison.
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