Re: new electric motor technology: One of my Navy friends suggested if I do not write this now it might never get written. I understand my reading audience might be quite low; but here goes. About 1993 the Navy decided that, for lots of reasons, they would need a significant increase in electrical power generated in its future warships. The next warship coming down the pike would be the DDG 1000, now named the Zumwalt. It is under construction in Bath, Maine and has recently been launched. For electric power generation the Navy looked at five possibilities. Induction Motor: This was the current technology. It was large and heavy, and easily eliminated because three other technologies looked somewhat promising. Improved Induction Motor: This would be the fallback option in the event that none of the three new technologies panned out. It would be the existing technology with whatever new improvements seemed appropriate. It was low risk, but would still result in a large heavy installation. DC Homopolar Motor: This was the highest risk of the three technologies because its development time was projected as the longest and some technical issues had to be overcome. Theoretically, it might prove to be the best in the long run, but for now the Navy would keep the effort going with some relatively low level of funding. Over the next five to ten years, this decision to not take this approach proved to be the best one. The theory remained great, but the manufacturing issues continued. Motor brushes were a significant issue. The design would require the best brushes in the world, better than any that had been developed to date; and they would need to be perfectly aligned. Permanent Magnet Motor: Small permanent magnet motors were being used more and more in numerous applications. Scaling the motor up to the size needed would be a tremendous challenge, but the Navy decided to proceed on this route. High Temperature Superconducting Motor: This was also a new technology that would require a significant scaling up in size. The navy perceived it as a higher risk than the permanent magnet concept, and perhaps rightfully so with the exception of one effect that I will mention later. However, there was enough interest to increase their research and development efforts. During full scale testing the Permanent Magnet Motor suffered a catastrophic failure. In rapid fashion the Navy decided to change to the Improved Induction Motor. It would require a significant change in the ship design, including the loss of space that had been planned for other purposes. In fairness the Permanent Magnet Motor team made a strong pitch to repair and retain that design. Although not a member of that technical team I did feel that their approach would have been preferred over reverting back to an induction motor design albeit improved. However the best approach would have been to adopt the High Temperature Superconducting Motor design. I was a member of that technical team. Unfortunately, we were not consulted, nor to my knowledge was our sponsor in the Office of Naval Research. The DDG 1000 Program Management apparently made the decision without consulting us. Superconductivity was discovered in 1911. In essence, when the temperature in an electric circuit gets very close (perhaps 4 degrees Kelvin) to absolute zero (0 degrees Kelvin, -273.15 Celsius, -459.67 Fahrenheit) the resistance suddenly goes to zero. The resistance does not merely decrease, it goes to zero, something that is simply not possible under our laws of physics. So we are now in the realm of quantum physics. In addition, it is difficult and costly to maintain this temperature; requiring the use of liquid nitrogen as a cooling agent. For decades the research community searched for a conductor that would superconduct at some temperature higher than -459.67 Fahrenheit. If that temperature could be raised 30 degrees or thereabouts, we could get away from the use of liquid nitrogen. In the 1980s, such a conductor was discovered and it was off to the races, at a slow scientific pace. Eventually the Office of Naval Research contracted with American Superconductor to put together a team to construct a 5MW motor, a tremendous size increase from the much smaller laboratory models. The result was so successful that, even before the full testing was completed the team was asked for a technical opinion on how much larger the next motor should be. After much discussion around the table about doubling the size, or even tripling it, we told the Office of Naval Research that an increase of four times would be the upper limit, that is a 20MW motor. ONR came back with a decision to contract for a 36.5MW motor which happened to be the size needed for the DDG 1000. To the surprise of many we were successful. The motor was delivered to the Navy test facility where it eventually exceeded all test criteria. Before the testing of the superconducting motor was complete the permanent magnet motor failed and the DDG 1000 Program Manager almost immediately decided to revert to the improved induction motor. Unfortunately, that decision will detract from the ship capabilities for the rest of its life. The 36.5MW High Temperature Superconducting Motor was ready for the DDG 1000. Those of us on the team knew that it would have been the best choice. Earlier I mentioned a significant difference between the Permanent Magnet Motor and the High Temperature Superconducting Motor. The former has a catastrophic failure mode, which unfortunately occurred during full scale testing. There was an erroneous perception that the High Temperature Superconducting Motor has a catastrophic failure mode in the loss of the cooling medium. Such is not the case. First, it is highly unlikely due to the use of multiple cooling heads. Second, if all cooling were to be lost the motor will remain in a supercooled configuration for many hours and continue to function, perhaps for as long as a day.
Posted on: Sat, 15 Mar 2014 09:35:54 +0000
Trending Topics
Recently Viewed Topics
© 2015