Talk:Flux switching alternator

Use with Gas Turbines

This article asserts that flux switching alternators are widely used only in missile applications. It seems that the article should explain why they are not (are they not?) used with gas turbines in integrated electric propulsion applications. Mcarling (talk) 16:38, 10 September 2012 (UTC)

If you have sources that this type of alternator is used elsewhere, then please add it. Integrated electric propulsion and its sources are pretty quiet on their generator technology. Andy Dingley (talk) 16:46, 10 September 2012 (UTC)

The only thing I could find was this: http://www.dtic.mil/docs/citations/AD0917915 Mcarling (talk) 17:00, 10 September 2012 (UTC)

Interesting - that's much more power (5,000 hp) than the missile alternators, or anything I've seen in relation to these. I'm somewhat surprised - much of the flux-switching alternator's advantage is because it's small and robust, hence missile-suitable. This suggests that it's also being used simply because it can handle the high speeds. Andy Dingley (talk) 17:19, 10 September 2012 (UTC)

Small and robust are good characteristics for naval applications, but the big advantage would be elimination of the reduction gears. Naval gas turbines that I've seen have shaft speeds from about 15,000 to about 24,000 rpm. Naval electrical systems are usually 400Hz, so I cannot think of a reason why flux switching alternators would not be suitable, possibly ideal. Mcarling (talk) 17:39, 10 September 2012 (UTC)

I just found US Patent No. 3,912,958 which seems directly relevant. http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN/3912958 Mcarling (talk) 18:18, 10 September 2012 (UTC)

In the naval context: "An obvious benefit in using direct coupling stems from the removal of the gear box, but the use of permanent-magnet excitation in synchronous generators allows a considerable reduction in size and improvement in efficiency as compared to conventional wound-rotor generators (which require an exciter that adds to size and losses). In addition, direct coupling allows the generator to run at the highest speed possible and results in a smaller size since output power of synchronous generators is directly proportional to speed. ... There are several permanent-magnet topologies that include radial, axial, and transverse flux topologies with variants in the way magnets are mounted or imbedded in the rotor. These topologies eliminate the need of an excitation winding and reduce the overall losses and size of the rotor. In this study we considered the surface-mounted radial flux permanent-magnet topology." http://esrdc.mit.edu/library/ESRDC_library/Vijlee-Directly-IEEE-2007.pdf Unfortunately, the authors did not indicate why they chose the radial rather than the axial or transverse flux topology. I cannot find a Wikipedia article that discusses the advantages and disadvantages among these three topologies. Should that be discussed in this article? M Carling 16:50, 12 September 2012 (UTC)

This is falling foul of a common problem, that narrow technical sources see something as "so obvious" that they don't bother to make them clear enough for the wider audience. These large naval alternators are certainly interesting, and WP ought to cover them, but it's not quite clear just what they are.

To produce a clear definition for a flux switching alternator, it's firstly one that works by switching flux. I would state this as, "An alternator where the rotor acts as a flux switching element; both the field generation, either permanent or field coil, being mounted on the stationary frame, as are the output windings."

For these naval alternators, it's clear that they're permanent magnet fields, but it's not clear to me if they're a permanent magnet rotor, or a non-rotating field with aflux switching rotor. Andy Dingley (talk) 19:52, 13 September 2012 (UTC)

Gyroscopes

"This is dubious because missiles use laser gyroscopes (which don't require acceleration to speed), not rotating gyroscopes."

Modern missiles might, older missiles spin. Plenty of missiles with rotating gyroscopes are still in service. Besides which, laser gyroscopes aren't instant-on devices either. Andy Dingley (talk) 21:14, 13 September 2012 (UTC)

When Brassey wrote in 1987 or 1988, there were probably some old missiles still in service with rotating gyroscopes (that would need to spin up). I believe all or virtually all missiles in service today probably have laser gyroscopes (that don't need to spin up). I think we should simplify that sentence by removing the clause about gyroscopes -- unless a 21st century source can be found to support it. M Carling 02:44, 14 September 2012 (UTC)

Do you have any specific examples of missiles still in service which use rotating gyroscopes? M Carling 02:50, 14 September 2012 (UTC)

I've just spent a few hours reading about gyros and my concern has been eased somewhat, for two reasons, the main one being that modern fiber-optic gyros need a few hundred milliseconds from power-on until they begin transmitting valid data. The other reason is that I had failed to make the distinction between fiber-optic gyros (which began production in the mid-1990s) and ring laser gyros (which began production in the late 1970s). I specifically propose to replace "to allow gyroscopes to be accelerated to speed" with "to allow gyroscopes time to begin delivering valid data". M Carling 06:05, 14 September 2012 (UTC)

• It's sourced. It always was.
• It doesn't matter if it's true now, because it was true once, and that's still valid within the context of this article and doesn't stop being valid. This is not an article about "the current state of missile guidance", it's an article about a type of alternator, a type of alternator that had greater prominence in the past than today. In this alternator's heyday, gyroscopes spun.
• Military kit hangs around for a long time. For the oldest missile guidance in service, look at Warpac-supplied naval missiles. Andy Dingley (talk) 09:07, 14 September 2012 (UTC)