How a “reliable mermaid” turned the subsea power vision into reality during shallow water testing
Testing of subsea VSD proves reliability of concept as Joint Industry Project team push boundaries of traditional product development.
One crisp, sunny morning in November, Sari Grano, one of ABB’s operations managers, sent an ice-cold bottle of champagne crashing into the side of a subsea variable speed drive (VSD), affectionately naming it “Durus” or “reliable mermaid”.
The ceremony at a harbor in Vaasa, on the west coast of Finland, signaled the start of shallow water test for the first full scale prototype of a subsea VSD. It marked the latest milestone towards the vision of an all-electric subsea processing facility.
The test is the latest in a five-year Joint Industry Project (JIP), started in 2013, between Statoil, Total, Chevron and ABB. The JIP aims to qualify subsea medium-voltage switchgear, variable speed drives with associated controls and low voltage distribution, at depths of 3,000 meters. Transmitting up to 100 MW capacity some 600 km, takes subsea compression and oil boosting closer to the reservoir. Oil and gas production improves due to the increased flow and pressure of the stream. It frees up the limited space on topside installations. Costs are reduced by having one cable that is distributed to many subsea loads.
Furthermore, operational costs are greatly reduced, energy and CO2 emissions are lowered, while marine pollution is cut and decommissioning simplified.
As the team set about lowering the VSD into the 7-meter deep harbor, it was during the next 168 hours that the engineers would discover whether “reliable mermaid” was an appropriate name.
Designing such a highly complex system for use in an extreme environment demands such incredible reliability that maintenance or repairs are minimized. We need to prove to all parties involved that the entire installation is going to be ultra-reliable because pulling up equipment from 3,000 meters costs a lot of money
In addition to high reliability, a competitive subsea processing facility calls for reasonable cost, low weight and small footprint to enable handling and installation in different continents. Such conflicting targets requires a strategy not usually associated with traditional product development.
As a large R&D project, the JIP sees rapid technology transfer from research to equipment prototyping. To ensure a fast project delivery, ABB based the subsea power and control equipment on pre-existing in-house technologies that feature a long record of reliable operation and established quality control and obsolescence strategies.
While partly re-using existing core components, ABB provided dedicated packaging for subsea environmental conditions. New product assemblies derived from existing platforms but with reduced number of components and functions for increased reliability.
In addition, accelerated testing carried out to simulate some 30 years of a components life within six months. This was undertaken to demonstrate the long-term performance of critical components. Specific key tests are conducted immersed in oil, under full pressure and at elevated temperature for the duration of the design life targets. This is in addition to other stress conditions relevant to the component.
So is Durus a reliable mermaid? Well, following extensive electrical and thermal tests, we are pleased to report that the VSD passed with flying colors. We demonstrated the successful operation that have truly pushed the drive to its limits, proving beyond doubt that it is reliable. The shallow water test proved that the electronic and power components can meet the thermal performance demanded.
The next step is a 3,000-hour shallow water test of a complete subsea power system with two variable speed dives in a parallel, combined with subsea switchgear and controls, targeted for late 2018. The first installation of the subsea power products in the real offshore production site is expected to begin in 2020.