EMALS & JPALS for the JSF

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splittingatoms

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Unread post07 Dec 2017, 17:57

wolfpak wrote:The use of DC is probably because they don't have the technology to make AC work. It's a step back in my opinion. The auto industry abandoned DC for similar applications long ago because of the problems and expense of maintaining those systems.

From published reports the reactors on the Fords put out around 770MW compare to 525 or so on the Nimitz class. They're comparable to those in domestic power plants that are rated at 800MW. They may be smaller in size


Long time lurker (couple years now), first time poster.

I just want to chime in here on something I know pretty well (nuclear power plants)...the Ford plants likely have a thermal output (MWt) in the range posted. However, their electrical/propulsion output is probably around 28-30% of that. So let's assume maybe 215-230 MWe (288,000-308,000 HP).

A single-core, commercial nuclear power plant will range anywhere from about 1600 MWt for a small, two-loop plant to 4500 MWt for an EPR or APWR type plant. That will give electrical output in the range of 580-1700 MWe (775,000-2,275,000 HP).
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tincansailor

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Unread post07 Dec 2017, 20:48

Long time lurker (couple years now), first time poster.

I just want to chime in here on something I know pretty well (nuclear power plants)...the Ford plants likely have a thermal output (MWt) in the range posted. However, their electrical/propulsion output is probably around 28-30% of that. So let's assume maybe 215-230 MWe (288,000-308,000 HP).

A single-core, commercial nuclear power plant will range anywhere from about 1600 MWt for a small, two-loop plant to 4500 MWt for an EPR or APWR type plant. That will give electrical output in the range of 580-1700 MWe (775,000-2,275,000 HP).

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Welcome aboard splittingatoms. Interesting analysis. So a DC system would give you greater Shaft Horse Power? I was discussing this a couple of weeks ago with another old navy guy, with engineering experience. He was surprised the Chinese would try this because of the greatly added weight of generators, need for thicker wiring, and insulation, and safety issues. But your suggesting it may be worth it?

My thought was the breakthrough the Chinese were referring to might be room temperature super conductivity. We haven't heard much about that technology lately, but if they have made that kind of breakthrough it would solve some problems with the weight, but not the safety issues. What are your thoughts on the subject?
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wolfpak

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Unread post07 Dec 2017, 21:07

Splittingatom,

Thanks. I stand corrected. My 800 MW should have been qualified as electrical power out the door at one of the Midwest utilities. Mixing apples and oranges.
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splittingatoms

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Unread post08 Dec 2017, 05:38

tincansailor wrote:Welcome aboard splittingatoms. Interesting analysis. So a DC system would give you greater Shaft Horse Power? I was discussing this a couple of weeks ago with another old navy guy, with engineering experience. He was surprised the Chinese would try this because of the greatly added weight of generators, need for thicker wiring, and insulation, and safety issues. But your suggesting it may be worth it?

My thought was the breakthrough the Chinese were referring to might be room temperature super conductivity. We haven't heard much about that technology lately, but if they have made that kind of breakthrough it would solve some problems with the weight, but not the safety issues. What are your thoughts on the subject?


Sorry if I wasn't clear. My analysis was merely comparing the size of commercial scale plants to naval plants and making sure the difference between thermal and electrical Megawatts was understood and called out.

As far as AC or DC power for EMALS (and the like), I can't say I see any one system being superior or "cutting edge" over the other. Three phase, AC power has a lot of advantages in rugged simplicity. Power electronics can be minimized in many systems, voltages steeped up or down as needed, and motors can be off the shelf. DC power offers the potential for minimized transmission losses, however I'm not sure how much that buys you on a ship. Doing voltage transformations in DC is very well-established at this point, but it isn't as rugged or cheap as a transformer in my opinion (I am open to be wrong on this). I would imagine the EMALS system has DC as some point which is then put through something looking a bit like a giant audio amplifier to drive the linear motor. In the sense that a massive amount of power can undergo one less transformation, perhaps it's a benefit. With that said, the EMALS flywheels could already accomplish that with the right kind of motor/generator, i.e. taking in AC to spin them up and then outputting DC. Long story short, choosing DC doesn't illustrate any advantage or disadvantage in my eyes, nor does it make or break the coupling to conventional power sources.

As has already been mentioned, diesels and gas turbines are more than capable (actually more so than nuclear) of shifting power to meet demands. Like the Zumwalt has lots of extra electrons for lasers/railguns/etc., adding additional generation capacity for EMALS strikes me as no big deal. A single added LM2500 or MT30 turbine is a very small addition to the layout of the ship and is MORE than capable of running EMALS. It could even sit dormant until one wishes to launch aircraft and then be brought into action. I simply attribute the article above to typical journalist incompetence.

Perhaps the "innovation" is the use of high temperature superconductors. These certainly exist and work to bring sizes down. I can once again point to the Zumwalt, which has the largest superconducting motor on the face of the earth. It has also struggled with that FOAK technology and I'm sure a linear motor up on the deck would be even more "adventuresome" from a qualification and refinement perspective. HT superconductors still require liquid nitrogen for cooling, so there is a whole subsystem of cryo equipment and insulated lines which must exist. Leaks in these systems can be catastrophic to personnel safety and to other equipment. They can also cause the superconducting equipment to not superconduct. Should this happen, the arc-flash will do a nice impression of a bomb, with similar risks to personnel.

It is conceivable that China has devised a superconducting, DC EMALS system. If so, good for them. I don't see any actual advantages to what is currently on the Ford carrier. In a war environment, the KISS standard still applies. Fancy for fancy's sake didn't do the German's a lot of good in WW2 and it still won't today.
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steve2267

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Unread post08 Dec 2017, 06:04

That is a VERY NICE 2nd post. I too welcome you aboard! :D
Take an F-16, stir in a little A-7, bake, then sprinkle on a generous helping of F-117. What do you get? An F-35.
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