Gunnar Johnsen: magnetic personality
There’s an age-old technology that’s now stepping out of the wings to claim its share of the limelight: permanent magnet (PM) motors. But look behind Rolls-Royce Marine’s commercial development of PM units and one remarkably tenacious man stands out. By Stevie Knight.
According to Gunnar Johnsen, the trick is placing powerful magnets in the rotors. “While traditional electromagnetic motors still need some current to excite them, permanent magnet motors don’t,” he explains. “So you get much more efficiency, along with much less noise and vibration.”
But like most innovations, putting it out into the real world has not been straightforward. “In fact there have been a lot of ups and downs: when I started none of these products existed so everything had to begin from scratch.”
Johnsen has been involved in the long road to commercialisation since the concept’s inception. “My background is electrical and computer science and my first years were spent working on oil production rigs and FPSOs... usually on power and control systems of one sort or another.”
Then in 1998, he was offered a job with what was then Ulstein to develop the ship designer’s electric propulsion systems. New magnetic compounds, a further development of the rare-earth variety, had started to make it off the production line in the 1980s and the potential of installing a PM motor to encircle the rim of a thruster started to open up some useful possibilities for the marine environment.
A direct drive positioned around the circumference of a thruster means you don’t need to put it inside the vessel. “It’s cooled by the environment,” Johnsen notes, “and there’s no gearing involved.”
The process of getting any totally new product to market is very complex, he explains. Establishing a new supply chain and assembly process for both the sealing of the magnets and the bearings proved challenging. “These magnets are highly vulnerable to corrosion so you have to seal them properly against air and water.” Given that motors need to have a life of 20 years, corrosion protection beyond most common solutions was needed: in fact it took advanced plastics research to provide the answer.
Further, the bearings which seat the circular rotor are one of the few components that take a lot of wear – but again, they need to stand up to the same two decade lifecycle. While the team started off with an innovative type of water lubrication, “this wasn’t reliable enough – so we had to go back to a conventional, centralised lubrication system”. Johnsen says: “while you might think of it as only an electrical propulsion system, it takes a multidisciplinary approach”.
In fact it took till 2007 before a PM motor was finally installed as auxiliary propulsion on the first test-bed vessel, Octopus, and another five years before the team had moved it on to main propulsion: this came to fruition on the Gunnerus, the Norwegian University of Science and Technology’s research ship, installed last year.
After so long in the making “of course I was a bit nervous, watching the Gunnerus sail away from the yard with these two permanent magnet units installed” he admits, “but when it reached its home harbour and everything was still fine... that made for a very nice evening”.
Building up a robust product requires an open approach with the team behind it: “You need to give both challenges and responsibility together, this gets people get motivated.
“But you also have to push the technology beyond the boundaries, you have to see what fails and why it fails - so you have to push the limits and test it. You have to get people’s trust to be able to do that... if you have the right team, you find out why it didn’t work, and then you can start to build on it. They have to know they won’t automatically get sacked if something fails... then of course they see the opportunities - that there’s something to be learned from it.”
Johnsen certainly believes the time is ripe for PM motors to see a big take up in the marine environment, and Rolls-Royce’s long term investment in permanent magnet technology bodes well for the future. Certainly other sectors are now involved in large-scale installations: China for example has recently fitted the first PM drive on a tube train and according to reports, it is looking toward a traction energy saving of around 15%.
Fuel efficiency is one thing, but it pales beside the potential lifecycle savings: “We expect to see a reduction of 50% on the maintenance costs... given condition based monitoring that shows you the real demand.” It is, he says, a subject “under discussion” with the class societies.
But Johnsen is happy about the results: he says one offshore vessel has now had a permanent magnet application running for 5,000 hours with no maintenance at all, “and that’s a really good feeling”.
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