If Direct Conversion works...

[BenTC]

IOther than driving a free-electron laser, what could you do with raw HV-DC ?

I'm not sure what process you would put raw 132kVDC across, let alone raw 800kVDC. For instance http://en.wikipedia.org/wiki/Electric_arc_furnace indicates the max voltage used is 900V.

[BenTC]

Advantages of a HF power grid (with HF, I mean the 400-1000Hz range, like in aerospace): Less losses in transformers and smaller footprints (due to smaller cores), no health hazards from ELF radiation through transmission lines, possibility of three-phase transmission. Some people are sensitive for >100Hz pulsing of fluorescent and AC gas discharge lights running off 50Hz grids, this is also eliminated when using HF supply (most 'decent' fluorescent manufacturers also supply 400Hz, even dimmable, ballasts)

I would have thought a high frequency transmission line would suffer increased losses. Aerospace operate at much shorter distances than geographical and get a much greater advantage from lower weight and lower transformer losses. The same doesn't apply to a power grid where transmission line losses are significant. Also, the limiting factor the the length of transmission lines is often voltage regulation and voltage stability due to the volt-current phase shift that increases with both distance and voltage. Do you have some references to a high frequency grid? I'm interested in knowing more.

DC has safety issues (arcs when switching) and is difficult to step down or up.

This is somewhat true with circuit breakers, although this is handled by proper design and oversizing compared to AC breakers - its just a matter of providing sufficient arc lengthening and cooling mechanisms, and enough terminal mass for heat dissipation and repetitive wear. Its not an issue with solid-state switching, which additionally can shut down and drain the line charging current within one cycle, which is better than an AC circuit breaker.

btw, SMPS do operate at a high frequency internally, but what they output is DC.

[Stoney3K]

btw, SMPS do operate at a high frequency internally, but what they output is DC.

True, but the reason SMPS are used in most electronic devices today is because transformer/rectifier/capacitor arrangements are downright bulky for line frequency. With a higher frequency grid, transformers could be built into a more manageable form factor.

Some people are religious about their use of (toroidal) power supply transformers for audio amps, as SMPS do have quite a ripple on the output voltage, which is HF. But the actual arguments in favor or against SMPS in audio circuits is ambiguous.

I didn't think of the line capacitance effects at geographic scales for HF grids yet, that could pose a certain limitation on the grid efficiency. However, a transition from AC to a fully DC grid would be a major logistical and political enterprise, breaking most existing equipment. A hybrid design using a HVDC main grid with HFAC sub-stations utilizing conventional transformers could be a possibility here.

HVDC has a major advantage in the fact that it doesn't need to run any reactive currents (e.g. the power factor is always one), so the line capacitance is not an issue. Only the line resistance, which can be quite low considering the advances in high-temperature superconducting cables.

Has anyone ever thought of the idea of using a plasma stream to conduct electricity? In theory, a plasma stream has little resistance and might be easier to manufacture in the long run, as it doesn't require things like cryogenics to keep the superconductors operational. Only a magnet every unit of distance, to keep the whole thing contained in the middle of a tubular vacuum vessel (although I don't even know how much vacuum would be required here, I guess an atmospheric pressure nitrogen plasma would be a dream.)

[chrismb]

The only industrial use for 100s of kV that I know of is particulate extraction in dusty flues, and perhaps most such systems only use 10s kV most of the time.

[MSimon]

But now you're mentioning series of several devices, stacked gate to source. I can't recall any MOSFET or IGBT that will survive a gate-source voltage of 1MV or greater by itself.

They design the devices these days so that they conduct on over voltage. Repetitive avalanche capability. Turn on is not too big a problem. Turn off is where it gets interesting.

Photo triggered devices are very popular in utility DC to AC conversion systems.

[KitemanSA]

IOther than driving a free-electron laser, what could you do with raw HV-DC ?

I'm not sure what process you would put raw 132kVDC across, let alone raw 800kVDC. For instance http://en.wikipedia.org/wiki/Electric_arc_furnace indicates the max voltage used is 900V.

Well, at 4V per cell, you could run 200k Hall-Héroult process Aluminum reduction cells in series!!

[DeltaV]

On the Implications forum some of us were earlier discussing Polywell use for SSTO aerospace vehicles. One concept involved superconducting electromagnetic fans/turbines for low-to-medium altitudes/speeds (with a long-range atmospheric excursion capability included) combined with Dr. Bussard's QED-ARC engine (REB heating of ducted airflow, possibly with added reaction mass) for medium-to-high altitudes/speeds, all the way to orbit.

The idea of using a Polywell as the primary power source for all flight modes, without having to also carry hydrocarbon-fueled turbines, cryogenic chemical rockets, etc. has a lot of appeal. The low-to-mid altitude electromagnetic motors would require Polywell output voltage to be stepped down to a usable range, assuming that "electrostatic" motors, directly using the high voltage, are impractical.

My question for the EE-leaning Polywellers is this:
Does current, or near-future, semiconductor technology allow the possibility of reasonably low-mass conversion from MV to the lower voltages suitable for high power-density electromagnetic motors, with total power for all motors in the neighborhood of 100+ MW (any heavy reactor shielding, if needed, being conveniently ignored)?

[kunkmiester]

I think I mentioned that I figured a lot of processes would become viable with lots of power. I was thinking a lot about electrolytic metal purifying, wondering if some metals, like titanium, would be viable by such processes with cheap electricity. Right now they're expensive mostly because they use reduction reactions which produce lots of nasty byproducts.

How would water react, as in hydrogen production? Is there a particular voltage/amperage that it works best at?

[Stoney3K]

The idea of using a Polywell as the primary power source for all flight modes, without having to also carry hydrocarbon-fueled turbines, cryogenic chemical rockets, etc. has a lot of appeal. The low-to-mid altitude electromagnetic motors would require Polywell output voltage to be stepped down to a usable range, assuming that "electrostatic" motors, directly using the high voltage, are impractical.

Well, you could wire it up to a capital-ship sized Lifter and make some very pretty airships. Keep away from the hull though!

BTW: Turbines can be converted to run on H2, methanol, or any other substance that produces heat.

[DeltaV]

The idea of using a Polywell as the primary power source for all flight modes, without having to also carry hydrocarbon-fueled turbines, cryogenic chemical rockets, etc. has a lot of appeal. The low-to-mid altitude electromagnetic motors would require Polywell output voltage to be stepped down to a usable range, assuming that "electrostatic" motors, directly using the high voltage, are impractical.

Well, you could wire it up to a capital-ship sized Lifter and make some very pretty airships. Keep away from the hull though! ;)

Ion wind generators still produce some ozone. The idea was to avoid significant ozone production at low/mid altitudes, otherwise QED-ARC could be used for all flight modes. Ion wind would probably produce much less ozone than a REB, however, but would there be much thrust?

I'm also wondering if a sealed, electrostatic motor could be scaled up, and what kind of power you'd get:

viewtopic.php?p=28720&highlight=#28720

Because high voltage distribution around the vehicle would be difficult, you'd probably have to have just one whompin' big electrostatic motor, either driving the spatially-distributed lift fans/turbines via driveshafts or turning a low-voltage generator to power the superconducting electromagnetic motors.

BTW: Turbines can be converted to run on H2, methanol, or any other substance that produces heat.

True, but for extended operation at medium altitudes/speeds, which has operational/economic advantages when the origin and destination points on the ground are not well positioned with respect to the desired orbit, the essentially "unlimited" Boron11 fuel supply would be a major selling point.

[Stoney3K]

BTW: Turbines can be converted to run on H2, methanol, or any other substance that produces heat.

True, but for extended operation at medium altitudes/speeds, which has operational/economic advantages when the origin and destination points on the ground are not well positioned with respect to the desired orbit, the essentially "unlimited" Boron11 fuel supply would be a major selling point.

The problem is that a direct Polywell power source dictates a minimum ship (and hull) size, because the Polywell itself needs to be sufficiently large to produce net energy output. Which makes it impractical for cars, aircraft, shuttle boats and, in general, anything smaller than an oil-tanker scale craft.

Railway locomotives could house a Polywell if it can be made compact enough. Remember, a rail loco has a maximum width of about 1,8 metres outside.

H2 or Methanol will in such a situation only be used as an intermediate fuel, used to transport energy from the Polywell by chemical means. Combustion and turbine technology are very well understood and proven technology, so we don't need to worry about those. Large craft can be powered by their own Polywell (or two) without much trouble.

[DeltaV]

The problem is that a direct Polywell power source dictates a minimum ship (and hull) size, because the Polywell itself needs to be sufficiently large to produce net energy output. Which makes it impractical for cars, aircraft, shuttle boats and, in general, anything smaller than an oil-tanker scale craft.

The energy needed to go from ground to QED-ARC ignition at medium altitude, using multiple lift fans and turbines (no rush, there are several grams of Boron11 onboard), is far less than that needed to accelerate from there to orbital velocity of 17,500 mph. Allowing unlimited low-to-medium altitude atmospheric flight before reaching for orbit shouldn't be that big of a deal, if a way to use the high voltage directly without ozone, or transform it to a low voltage without adding too much mass, can be found. This is all assuming radiation shielding is not as problematic as has been expounded elsewhere.

I think it's too early to tell how compact a Polywell can be. Given the current lack of data and modeling equations, I still have hopes for a mini-Polywell-powered Corvette (well below a MW) for commuting to and from my Polywell-powered VTVL space hopper (multi-GW).

[DeltaV]

My question for the EE-leaning Polywellers is this:
Does current, or near-future, semiconductor technology allow the possibility of reasonably low-mass conversion from MV to the lower voltages suitable for high power-density electromagnetic motors, with total power for all motors in the neighborhood of 100+ MW?

Just to be clear, I'm talking about stepping down voltage for 100+ MW of power (at most hundreds of MW), used for the avionics, actuation, reactor thermal management, cabin/EE bay environmental control systems and most importantly the superconducting, electromagnetic lift fans and turbines, before the QED-ARC engine fires up for the kick into orbit, not conversion of the full Polywell output (GWs) that the power-hungry, high-voltage QED-ARC uses.

Something a bit smaller than this, please:




Regarding electric turbines, 400KW/20,000rpm/480V and 100KW/60,000rpm/480V non-superconducting motors, about 2 feet long, with magnetic bearings, are currently in production. The power would need to be increased by about a factor of 500 or more for a Polywell aero/space hybrid vehicle (unless lots of little motors are used), but these might be a good starting point:

http://www.synchrony.com/products/high- ... ators.aspx

[As before, I'm conveniently ignoring the oppressive reactor shielding mass requirements discussed elsewhere.]

[Nik]

Not to put too fine a point on it, sure would help if you could pulse the system to some extent. Being able to 'syphon off' ripple with a transformer gives you utility power at manageable voltage...

FWIW, some trains run on 16.3 Hz...

http://en.wikipedia.org/wiki/List_of_cu ... l_traction

That oddity aside, if your Polywell can match any of these AC/DC/Hz, you have commercial off-the-shelf hard-ware and application. Even better, if you could fit a polywell onto a low-loader goods wagon, you could propel a standard electric train 'off the grid'. No 'overhead' or third-rail hardware, no flash-overs, no earth-currents, no distribution problems...

{FX: Sigh} Brunel's 6-foot gauge would have helped, here...

[DeltaV]

Not to put too fine a point on it, sure would help if you could pulse the system to some extent. Being able to 'syphon off' ripple with a transformer gives you utility power at manageable voltage...

Good point. I've been assuming pure HVDC out of the Polywell (which implies steady-state operation), but using something like POPS, or modulating the direct conversion process, could provide an easier route to stepping down the HV.