massive megahertz multi megawatt magnetron

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hanelyp
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massive megahertz multi megawatt magnetron

Post by hanelyp »

Maybe crazy idea for voltage conversion of the high voltage from direct conversion: Since semiconductors to handle that much voltage aren't available yet, go to vacuum tube technology for the DC to AC phase of voltage conversion. A magnetron to handle the voltage, power, and desired frequency range for the job would be pretty big, even with inductively loaded resonators. But I expect the engineering would be pretty straight forward for a qualified engineer.

MSimon
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Post by MSimon »

The losses are high in a vacuum tube. In addition you would still have to stack them to get to 2 MV.

With semiconductors the problem is volume if you are using air as an insulator. If you are using oil the problem is weight and replacement of defective devices. For the initial converters I don't see either as a problem.

For shipboard use compactness is probably the critical item. For aircraft compactness and weight.

The BFR is going to be an engineering bonanza.
Engineering is the art of making what you want from what you can get at a profit.

jambaugh
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Re: massive megahertz multi megawatt magnetron

Post by jambaugh »

hanelyp wrote:Maybe crazy idea for voltage conversion of the high voltage from direct conversion: Since semiconductors to handle that much voltage aren't available yet, go to vacuum tube technology for the DC to AC phase of voltage conversion. A magnetron to handle the voltage, power, and desired frequency range for the job would be pretty big, even with inductively loaded resonators. But I expect the engineering would be pretty straight forward for a qualified engineer.
There are other "vacuum tube" methods as well. I wonder if the alphas could be fed directly into traveling wave tubes or staged klystron assemblies? .

One of the major losses in vacuum tubes is in the thermalization of the electrons in the hot cathode. At these voltages cold(er) cathodes could be used or as I suggest above direct use of the emitted alpha particles would bypass this problem. There is great flexibility in design and design innovation in vacuum tube designs. I don't see any intrinsic difficulties in designing near optimal efficiency power conversion this way.

I think the main issue would be space requirements.
Regards,
James Baugh

drmike
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Post by drmike »

20 to 50 MV/m are standard insulator capability. I don't think space requirements will be that big an issue.

MSimon
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Post by MSimon »

Dr. Mike:

You might want to look at this:

http://www.fingrid.fi/uploads/Construct ... /esite.pdf

Go to pdf page 4.

It is an air insulated 400KV DC converter. It is not small.
Engineering is the art of making what you want from what you can get at a profit.

KitemanSA
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Post by KitemanSA »

MSimon wrote:Dr. Mike:
...
It is an air insulated 400KV DC converter. It is not small.
The big part looks to be the AC portions. Will there be AC portions with the BFR, I mean at the plant as opposed to final distribution?

MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote:Dr. Mike:
...
It is an air insulated 400KV DC converter. It is not small.
The big part looks to be the AC portions. Will there be AC portions with the BFR, I mean at the plant as opposed to final distribution?
A lot will depend on whether DC distribution is the way to go. In any case for shipboard use AC will be required for the motors. Shipping "low voltage" AC around the ship is going to be safer than HVDC. In addition ships use a lot of 220 VAC 60 Hz (American ships) power.

For ships it would all be engine room stuff. For compact size on ships oil insulated converters are probably the way to go. Of course high pressure SO2 is also a possibility. Dr. Mike probably can chime in on that.

Oil has the advantage of better thermal conduction. So you solve two problems (insulation and cooling) with one technology.
Engineering is the art of making what you want from what you can get at a profit.

KitemanSA
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Post by KitemanSA »

MSimon wrote: A lot will depend on whether DC distribution is the way to go. In any case for shipboard use AC will be required for the motors.
Hmm. I thought most of the new high tech high power systems could go either way. Rail Guns, IPS, EMALS, all could do with HVDC. Not multimeg VDC, but DC. No?

MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote: A lot will depend on whether DC distribution is the way to go. In any case for shipboard use AC will be required for the motors.
Hmm. I thought most of the new high tech high power systems could go either way. Rail Guns, IPS, EMALS, all could do with HVDC. Not multimeg VDC, but DC. No?
All motors require AC. In the earliest motors this was obtained from DC by commutators and brushes. The field in the armature rotated. Now a days we do it with semiconductors/microprocessors and rotating magnetic fields in the stator.

Before Tesla no one could figure out how to directly use AC to generate the required rotating fields. These days it is so common that we have pretty much eliminated commutators and brushes in all but the very simplest and cheapest small motors. Slot car motors are a very good example of small cheap motors that still use commutators and brushes.

Rail guns require switching the coils as the projectile advances. The same for linear motors. This is a rotating field unrolled.

So even though the supply is DC the drive for the devices you mention is effectively AC. To continually accelerate the projectile the field must move.

Let me add that this is the barest outline and the details will vary according to the motor type.
Engineering is the art of making what you want from what you can get at a profit.

eros
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Post by eros »

MSimon wrote:Dr. Mike:

http://www.fingrid.fi/uploads/Construct ... /esite.pdf

It is an air insulated 400KV DC converter. It is not small.
It is twenty years old thecnology. I was small boy when they build it. I remember some articles and thinked why they want use DC to carry energy. It is so complicated to make AC (that time inverter was rarity, some new PC powers use it, transformer was common)

Nowdays are better semiconductors available and there is posible to use commutators and brushes to make AC. They don't have so high MTBF, but if make some proof of concept brushes are good enough and simple.

~1MV conversion is only minor broblem, it is not nessesary to brother. There is more important things to think.

~20Kv/cm rule is enough for test purposes. That converter station use long distances, because want arc stoping propeties better.
</ Eerin>

jambaugh
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Post by jambaugh »

drmike wrote:20 to 50 MV/m are standard insulator capability. I don't think space requirements will be that big an issue.
I was referring specifically to the space required for klystron/traveling wave tube or other vacuum-tube-esque conversion.
Regards,
James Baugh

jambaugh
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Post by jambaugh »

MSimon wrote:
KitemanSA wrote:
MSimon wrote: All motors require AC...

...Rail guns require switching the coils as the projectile advances...
Just to strain a gnat...

Technically a rail gun does not. It's a DC current through a circuit completed by the projectile. The B field pushes outward on the current loop and hence pushes the projectile forward.
Regards,
James Baugh

93143
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Post by 93143 »

I think he was thinking of a coil gun.

Just out of curiosity, how much would a 6 GW DC-DC converter capable of stepping down from 1.5 MV to maybe 1-10 kV actually weigh? How big would it be? Would it weigh more than a 6 GW BFR? A lot more? I suspect so, but I want to make sure...

KitemanSA
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Post by KitemanSA »

93143 wrote:I think he was thinking of a coil gun.

Just out of curiosity, how much would a 6 GW DC-DC converter capable of stepping down from 1.5 MV to maybe 1-10 kV actually weigh? How big would it be? Would it weigh more than a 6 GW BFR? A lot more? I suspect so, but I want to make sure...
MSimon and I were discussing compactness, primarily with respect to use aboard Naval vessels. I cannot currently imagine a Naval vessel that would require anywhere in the neighborhood of 6GW. Indeed, most Naval uses would be in the 100MW size that Dr B proposed to begin with (Navy funding, no coincidence).

Power electronics is not my gig, but don't variable speed electric motors like those that would be used for Naval propulsion all essentially convert supply power to DC and then reconvert back to proper frequency AC? If so, mayhaps a DC supply from the BFR would skip two evolutions and be a better fit to start with. Anyone?

MSimon
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Post by MSimon »

Rail guns so far do not have high MTBFs. The conductors erode. So I was thinking of longer life eqpt. But you are correct. By using "brushes" the field does move with the projectile.
Engineering is the art of making what you want from what you can get at a profit.

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