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A common rumor I've heard from some engineers is that much of the grid is synchronized using GPS signals, and if enough satellites were jammed or disabled, it would wreak havoc. Bullshit, right?
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Sep 10, 2011 02:42
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So has anyone here actually worked on or in thyristor halls? They're the one part of super-high power electronics that really blows my mind. How the hell can you trigger hundreds of devices in a balanced, consistent manner and not just blow everything up? What the hell happens when a thyristor stack fails, anyways?
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Sep 13, 2011 03:25
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helno posted:The rotor is much harder to keep cool. The way most are cooled is by high pressure hydrogen gas. Hyrogen is used because it has a really high specific heat capacity but causes very little drag on the rotor. So the rotor just spins in this cloud of gas and large fans on the rotor force the hydrogen through chillers. God drat I had no idea this was done. If someone ever suggested to me using hydrogen gas for cooling electronics, then I would think they were insane. I've actually known of some large accidents that have happened in chemistry and combustion labs where people used hydrogen in the vicinity of brushed motors (which were driving the pumps, loving idiots) and... the results were disastrous. Obviously brushed motors are worse since they produce sparks all the time, but in a high power induction motor I can't imagine how they suppress ignition reliably. edit: also I know that hydrogen has great specific heat, but specific heat is joules per mass, not per volume. Is it really better than water then, when you consider that water is much denser even at high pressures? ANIME AKBAR fucked around with this message at 05:16 on Sep 19, 2011 |
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Sep 19, 2011 05:13
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Aliass posted:I find this very hard to beleive i have never EVER seen a dc or a 3phase slipring motor used to drive a pump (under 100kw). They are far more expensive then a generic 3phase ac motor. As thus i cannot understand why someone would use them in a laboratory situation. Hazardous/flammable environements are why explosion proof motors were designed. ANIME AKBAR fucked around with this message at 14:25 on Sep 19, 2011 |
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Sep 19, 2011 13:23
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modig posted:Yeah. So far he just has components, and no power supply. At some point he'll have to write up an saftey review and standard operating procedure for the system (a pulsed magnet for low field MRI), and that will get reviewed by some people up the chain. Since nobody in our group knows much about high power electronics, I suspect they will find some other people in the organization to review it, or pay someone from outside to look at it. Just curious, is he doing prepolarized MRI?
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Sep 22, 2011 03:07
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modig posted:Yeah. Let me guess, Stanford? If so you're lucky as hell to work with some of the best engineers in MRI. I'm jealous. ANIME AKBAR fucked around with this message at 04:38 on Sep 27, 2011 |
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Sep 27, 2011 04:31
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Frozen Horse posted:You want to see crazy water-cooled, high-current, high-magnetic field stuff? Check out these resistive electromagnets: Frozen Horse posted:The superconducting magnets are at a few microvolts and ~100 A. Because they have many more turns of wire, the field is stronger. The very slight voltage drop is from junctions between superconducting domains in the solenoid cable and results in a slow drift of the field strength on the order of ppb - ppm / day. This drift rate is enough so that for NMR spectroscopy, the instrument's RF circuitry is frequency locked to the resonance of the solvent so that successive scans aren't skewed from one-another. quote:The RF side of things is also interesting, since there are several mutually incompatible requirements such as a high pulse strength to more effectively excite the sample, yet then the signal must be acquired by very sensitive (60 db or more) pre-amps, a resonant coil that should have a very short dead time for the excitation to die down before the sample relaxes, yet a very high Q-factor for coupling to the sample's emitted signal...
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Oct 9, 2011 00:56
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| # ¿ May 3, 2024 12:03 |
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Frozen Horse posted:The reason for these is that they're the only way to get field strengths that high. A superconductor will have a critical field strength above which it will quench at that temperature. So, if you want to do something at 35 Tesla, that's your only choice. I expect that they're also good for crazy pulsed-field experiments where the field is ramped up from zero quickly. I'd also expect that after a year and a half at somewhere like the national high-field magnet lab, any given magnet would have a better design ready to supersede it anyway. quote:I'm not sure how possible that is. Sure, they might have eliminated ohmic drop through cunning superconductor assembly, but there is still a voltage drop due to flux motion resistance. Not enough to worry about unless you're starting to nudge up against the critical current, though. quote:What kind of magnet-fiddlery do you do?
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Oct 9, 2011 04:10
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