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I believe that to be bullshit. The power grid pre-dates GPS considerably, and what is important is that you're synchronized to the frequency and phase of the grid where you are. I do have a question, why 50/60 Hz? Both why do some places have one vs. the other, and why these two as opposed to 120 Hz or 75 or 400?
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Sep 10, 2011 04:04
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Three-Phase posted:400hz is used in aircraft, because you can make much lighter transformers than at 60 or 50hz. Interesting. This is making me wonder about the usefulness of designing sound, lighting, and power-generation equipment for portable-generator driven outdoor festivals (or raves, etc.) to work at 400 Hz. Lighter amp-stacks to load and unload, less of the expensive copper wiring and permalloy in the amps, easier-filtered mains hum, and one can always run it off of some sort of inverter when there is mains power available. Is this complete crack-pottery?
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Sep 10, 2011 19:34
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Three-Phase posted:I'm not sure how much the 400hz would impact things like cabling to transmit power. Plus the big problem is that almost nothing runs natively at 400hz. True, I've just read http://en.wikipedia.org/wiki/Utility_frequency, and the rabbit hole seems even deeper. It seems like reactive power loads scale with the frequency, so 400 hz loses for long-distance transmission. Then again, for this application, the longest cabling run I can conceive of would be a few hundred yards from generators to stage lights or amps at a large festival. Would operating at 400 hz make it easier to simultaneously standardize on ~200 V vs ~100? Could the reactive load issue be avoided by using cabling with the correct characteristic impedance (disclaimer: the closest I come to power transmission professionally is getting weak RF signals through coax from spectrometer to pre-amp)? Compared to 60 hz, there is almost nothing at 400 hz, but there is some MIL-STD-704 and other rather weird-beard gear out there like this concrete-saw company: http://www.pentruder.com/en/400hz-technology__78. Audio also has its own weird world of incompatible gear, witness the PowerCon connector, this would just add another layer of weirdness. Sorry for the derail. More topically, have you ever worked on/with/around aluminium smelting equipment? I've heard of aluminium metal referred to as "solidified electricity" due to the amount of energy required to reduce it from ore.
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Sep 10, 2011 22:43
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Streetlights, how do they work? Are they wired into the local circuit for the street that they're on? Do they mainly exist to keep enough load on the grid at night? Given that most are either sodium vapor or metal halide lamps, what kind of load are they? Could we do that in a way that produces less light pollution?
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Sep 15, 2011 06:52
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Three-Phase posted:2. The turbine must also immediately be tripped. When the circuit breaker opens, it's like having the driveshaft from an engine snap. Now there's nothing to absorb the energy, and if corrective measures are not taken, the turbine could accelerate until it blows apart. Then you may need to do something with the excess superheated steam, like blow it off. Not sure how they safely do that at a boiling-water reactor. I think the steam in a boiling-water-reactor would be throttled to the condenser, bypassing the turbine. The interesting problem becomes how one keeps the coolant pumps going to re-inject the condensate into the reactor and flow outside water through the condenser. On Hydrogen-cooling, hydrogen doesn't have that great a heat capacity, especially on a volumetric basis. What it does have, is a very low viscosity. This means that the friction from the flow induced by the relative motion of the rotor and stator is minimized. The improvement in efficiency from this is enough to justify filling generators and large motors with a flammable gas that leaks very easily due to its low viscosity. It also has higher thermal conductivity than other gases. Besides, if one's power-plant carks it, the added excitement from burning hydrogen won't matter too much compared with the stored energy in the form of rotational inertia and current flowing through large inductive circuits. Sometimes water can create problems before it even gets to the electricity: http://en.wikipedia.org/wiki/2009_Sayano-Shushenskaya_hydro_accident
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Sep 20, 2011 04:33
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helno posted:As to water chemistry we get the added bonus of our PHT and Moderator water containing tritium. We spend alot of time in positive pressure suits to avoid that. Look on the bright side, it's not a graphite-moderated reactor. My pet favourite nuclear reactor design (not yet implemented AFAIK), remains the sub-critical accelerator-driven energy amplifier.
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Sep 23, 2011 06:14
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That's a very interesting video. How do current-limiting breakers and fuses work? As I understand it, a regular fuse is a length of wire made of a low-melting alloy with sufficient resistance so that it will melt due to resistive heating above its rated current. Other added tricks involve the wire being under spring tension to widen the gap rapidly to prevent arcing. What gets added to give it magic current-limiting powers? If it's just a 1-ohm resistor in series, I'm going to be disappointed.
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Sep 24, 2011 04:00
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Three-Phase posted:I've worked with high-current low AC voltage before during some special testing. As far as magnetic fields being so high it can bend stuff, it's possible, but it's much more likely during faults. You want to see crazy water-cooled, high-current, high-magnetic field stuff? Check out these resistive electromagnets: http://www.magnet.fsu.edu/education/tutorials/magnetacademy/makingmagnets/fullarticle.html Under steady-state operating conditions, these will produce fields of up to 35 Tesla, which is about 100 times stronger than the rare-earth magnets found in hard drives. To do this, up to 40 kA will be passed through them, dissipating approximately 20 MW at a power density requiring cooling water to flow through the magnet at 45 mph. Without cooling, the magnet would melt in hundredths of a second. The magnets I usually use are only ~100 A, but they still provide ~12 Tesla at very stable field strengths. They also require no electrical power once energized because superconductors are cool like that. Would you like to know more? http://www.fmp-berlin.de/schmieder/teaching/vorlesung_mms/pdf/bruker_magneten.pdf http://www.jeolusa.com/RESOURCES/AnalyticalInstruments/NMRMagnetDestruction/tabid/390/Default.aspx These are fine magnets, unless the superconductor quenches. At which time it becomes a resistor in series with a very angry inductor (itself) and dumps all of its stored energy into boiling any remaining liquid helium coolant. This event is announced by loud bangs from the pressure-relief discs, clouds of fog from the release of lots of cold gas, and a mad scramble for the exit with whatever air you happen to have in your lungs at that very moment. Helium is not toxic, but since it is pure and contains no oxygen, is deadly. A lungfull can deplete the blood oxygen level enough to make you pass out as your lungs happily exchange oxygen outwards.
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Oct 7, 2011 08:33
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According to that site, the resistive magnets are flowing tens of kilo-amps and dissipating 10 - 20 MW, so I would guess a voltage of ~1000 V DC. 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. 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 7, 2011 18:14
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ANIME AKBAR posted:I never thought I'd see something more ridiculous than existing high field superconducting magnets. What could possibly make high field resistive magnets economical? It sounds like the power consumption would match up to the operation costs of superconducting cryogens. And that site says they only last one and a half years before needing to be scrapped, which is poo poo. 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. ANIME AKBAR posted:Agilent is claiming that in their magnets there is no voltage drop whatsoever, and every solder joint and switch is superconducting. Still have to helium/nitrogen fills every month or so. 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. ANIME AKBAR posted:This is the poo poo I deal with on a daily basis. Need a Q of 50 and a dead time of 20us, with one transmit/receive coil. Tedious as hell to design... What kind of magnet-fiddlery do you do?
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Oct 9, 2011 02:50
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Three-Phase posted:Yeah, that's what I was talking about. The way I initially described it does, as the other poster said, sound like utter nonsense. It's not that crazy. Chemically, it's similar to a rechargeable alkaline battery, except that it uses aluminium instead of zinc. This change increases the voltage per cell in the battery, but requires non-aqueous electrolyte conditions. So, you use your solar/wind/etc. intermittent source to charge these batteries when there's an excess of power, and then discharge then through an inverter in lean times. For grid storage, I think a sodium-sulfur cell would be better, since size and weight are less of issues than the cost per kWh stored. I also suspect that the future of this sort of thing is best done in a decentralized fashion, with moderate-sized battery banks allowing large customers to buffer their demand.
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Dec 30, 2011 21:24
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Groda posted:I think the idea was for Yeah, at the moment the metal is worth more than the electricity you could get out of an aluminum-based battery in most places where you would want electricity. If fossil fuels were to become more expensive or if fossil fuel users were required to store their emissions somewhere other than the atmosphere, the situation could change. Then instead of tankers taking oil from Arabia to wherever and returning in ballast, you'd have container ships taking aluminum from Iceland and bringing aluminum oxide back again. In the pacific NW, there used to be a lot of aluminum smelting (thus why Boeing set up shop there), but the local demand for electricity makes in uneconomical.
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Dec 30, 2011 23:57
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Cheesemaster200 posted:I found the label making tool in SKM today.... That's up there with the "Do not stare into beam with remaining eye." laser warning sign I saw outside one of the labs when I was an undergrad. On the other hand, if it can set your shirt on fire, you probably don't want to have your cornea focusing it on your retina.
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Jan 17, 2012 08:07
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How does a ground rod ground? Is dirt more conductive than I give it credit for? Does the answer depend on the dirt? I suspect that driving a ground rod into a dry sand dune won't do much.
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Jan 18, 2012 06:30
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Stonelegs posted:When you're demoing old duct bank or conduit, how do you tell if a line is live without putting someone in danger by accessing it? This assumes you have no drawings and no idea what's in the ground. If there's current flowing, it should have a detectable magnetic field. If it's energized DC at open circuit, this becomes an interesting problem. Then, you might want to consider tracing the conduit to build up your own "as-built" drawings. The bad-movie option: sever the conduit with a linear shaped charge. If the explosion is followed by arcing, it contained an energized circuit. On the other hand, you're at a safe distance provided that you didn't use wires to trigger the charge.
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Feb 3, 2012 08:09
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Three-Phase posted:In a lot of installations, the circuit breaker and relay control power runs off 120VDC. This is so you can have a bank of batteries to run the breakers even if there's a power outage, and if need be, you can get car batteries out of ten people's cars and operate the breakers in a pinch. In real life, the circuit breakers and critical power systems in Jurassic Park would probably have been run off 120VDC, so that whole priming thing would have been unnecessary. The 120VDC system allows a facility to "pull itself up by its bootstraps" in the event of a power failure. Why not just drive the controls off of the line feeding the breaker (appropriately stepped-down)? If it's dead, then the breaker controls are a moot issue. Three-Phase posted:It's odd too, you have a little cardboard box smaller than a half a loaf of bread containing a device that costs over $10,000. If I ran ABB, those would ship in a ruggedized attache case, not a $1 cardboard box. But that's just me. That's one of the things I like about one of the instruments we've got around the lab (an oxygen-content sensor). It was in that price range, and took several months to ship for reasons not exactly clear, but when it arrived it came in a very spy-movie style aluminium briefcase.
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Feb 20, 2012 04:04
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Crackpipe posted:I can't imagine surviving very long in a place like that. Familiarity breeds complacency and all that. I'd go for one of the upper switches and... *zap* Brushed my hand on one of the lower ones. I think this is one of those things to be touched only with a ten-foot pole.
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Mar 27, 2012 20:14
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Can you take pictures with a convenient angle/zoom to them?
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Mar 29, 2012 04:08
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Speaking of things seen about the neighbourhood, I was on my way to work today and saw some linespeople at work. On some of the lines, there were what looked like bright orange sleeves. I assume they weren't just feeling festive?
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Apr 6, 2012 02:01
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Three-Phase posted:It looks like, using his right arm, he reaches in and manipulates something, then reaches back in, and as his arm reaches the end of motion, the arc flash occurs. What is funny/creepy: after the arc flash, there does appear to be a worker nonchalantly walking behind the panel that just had an arc flash and is spewing smoke like nothing unusual has happened. Maybe at this workplace this is what nothing unusual happening looks like. With the arc-resistant switchgear, why have the panel on the same chassis as the medium-voltage gear? It seems like with some longer wires it could be in a nice air-conditioned control room. Also, are dapper bow-ties included or must they be ordered separately? Frozen Horse fucked around with this message at 08:56 on Apr 9, 2012 |
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Apr 9, 2012 08:50
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grover posted:Legend has it that clip-on-ties were invented for safety. Specifically, I've heard of IBM having a tear-away tie designed to prevent their field service technicians from getting pulled into the paper feed of their printers. This from back when field service technicians were expected to wear ties, and the printers involved were attached to early mainframe computers capable of handling data fast enough to print out phone bills for the Chicago area each month. No mere desktop printer, those.
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Apr 9, 2012 22:33
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coffeetable posted:Electrical porn: one of ITER's (the fusion project going on in the south of France) press releases this morning was on the their switchyard. Plus a technical presentation if you're so inclined. 400kV supply, 500MW pulsed draw and a short circuit power of 10GVA How many feet of concrete is appropriate arc-flash protection for 10 GVA?
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Apr 21, 2012 03:52
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Three-Phase posted:Removing links LIVE at 138kV That arcing, is that from just the capacitance of the link and breaker?
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May 18, 2012 15:27
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grover posted:I lost 3 loving motherboards at work to that poo poo. You'd think the contractor responsible would have switched suppliers or something, but, no, they bought a 10 year supply in bulk or something The monitor on my desk at work right now is a nice LCD that I pulled off the junk cart. It had been pitched because it was flicking on and off in about 1 second intervals. After unsoldering and testing the caps in the power supply pcb, I found the one that had failed. The replacement capacitor came from a computer power supply that was kicking around the closet. Now it works.
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Sep 5, 2012 04:53
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Cheesemaster200 posted:I am more concerned about single phasing with fuses. However if you are using them in a MV distribution setting for something which isn't a wastewater treatment plant, they are usually much easier to coordinate and provide better protection, as well as cheaper. Why not a wastewater treatment plant?
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Oct 24, 2012 19:41
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The stress response to low socioeconomic status associated with neighbourhoods with lots of overhead power lines is associated with cancer. But tackling that that would involve problems that can't be solved by NIMBYism.
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Nov 14, 2012 17:56
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Stored energy in disconnected systems. This can range from the obvious such as batteries and capacitors, through subtle cases like rotational inertia of motor-generators, to weird stuff like superconducting solenoids. Also, X-ray hazards from vacuum HV discharges.
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Jan 25, 2013 07:44
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babyeatingpsychopath posted:I hope someone can answer this here. Electric train track will often have sections with insulated breaks between them. It's set up so that the part of the train on one section can drive the remainder across the break. The reason is usually more about voltage drop and maintenance issues than phase, since the wavelength of 60 Hz electricity is rather long (although inductors such as transformers will introduce phase shifts).
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Mar 3, 2013 23:07
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How does the skin effect behave on non-cylindrical conductors? Suppose I have a rectangular bus-bar and start cranking up the frequency. Will the current be forced to the narrow edge as well as outward generally? What kind of wacky current distribution would an I-beam have? Does it matter much so long as the wavelength is long relative to the cross-section of the conductor? On the Superdome thing, it's a hidden feature that relays will trip when exposed to sustained current above their set-point?  From the description of the relay, it sounds well-documented and straightforward:1: Relay conducts and all is well 2: Current exceeds setpoint, timer starts 2.5: If current drops below setpoint and is above 3.5 A, timer expires uneventfully 3: If current is above 600 A, relay remains closed and declines the opportunity to self-destructively open 3.5: If timer expires and current is still above setpoint but below 600 A,  4: If current drops below 3.5 A while the timer is running, If anything, the weird feature to me is that a setpoint above 600 A will cause the relay to only trip on the low-current condition.
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Apr 3, 2013 17:37
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John McCain posted:100% or near 100% pure hydrogen is too rich to burn, and it has awesome properties for cooling for a gas. Yeah, hydrogen is awesome. Low viscosity for less drag on rotating parts, great thermal conductivity, a breakdown voltage almost as good as nitrogen, very rapid arc-quenching, and you can generate it on-site from electricity and water. There are some ways that hydrogen is crap. It leaks easily, has a wide flammable range, embrittles certain metals (mostly steels).
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Apr 26, 2013 18:26
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Three-Phase posted:Even if he was wearing Level 3 or Level 4 PPE, I'd still think this procedure was absolutely nuts. I have to show the guys at work this; their jaws will drop. If we ever attempted anything close to this we'd be seriously risking termination. A very low-impedance termination to ground, I presume?
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May 20, 2013 16:00
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Pvt Dancer posted:When (for example) an undervoltage relay keeps opening the switch, jamming a screwdriver in there can prevent the mechanism from opening. Pretty useful when faultfinding or in a pinch like this, although this is very much an unofficial solution that for some reason seems to pop up in accident reports a lot. If the circuit behind the switch is also on a sinking ship, one may as well keep the emergency bilge pumps, etc. on until its "Last one out, take your screwdriver with you."
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Jun 30, 2013 21:02
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Three-Phase posted:This YouTube Video of a nuclear power plant simulator. It's a neat video, but man there are a lot of different sounds at the same time. They also need a way to make the lights stop flashing, or a way to acknowledge the board, that makes the lights stop flashing, and then only new problem cause the lights for that new alarm that came in to flash. (There are entire books written on alarm management like this.) GENERATOR TRIP  REACTOR TRIP  OPERATOR TRIP 
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Jul 2, 2013 02:56
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AmbassadorTaxicab posted:MRI talk, what are the typical power requirements for a scanner? Is it variable for each scan mode? How much electricity gets used per scan? There's a lot of idle power for the consoles, HVAC, etc. The magnet itself consumes only cryogens once it's powered up. The gradient coils could consume a fair bit of power, since they're essentially just big electromagnets attached to a really kick-rear end stereo system. The RF coils can't put out too much power, otherwise you end up cooking the patient.
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Jul 8, 2013 21:52
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squeakygeek posted:Doesn't it stay powered up all the time? There are some MRIs on trucks that are shared between hospitals, these are quenched before moving them. I don't know how that ends up being worthwhile with the need to carefully ramp the field back up and recalibrate everything each time.
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Jul 9, 2013 17:57
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Three-Phase posted:This will be neat for people who have never seen this: here are some examples of big The highest voltage circuit I've been around lately was a bit more than that, but only about 100 mA. On the other hand, it was a 100 mA beam current at 7 GeV or so. At that point, it's a beam of electrons in ultra-high vacuum. You know it's high voltage because it gives off X-rays when going around corners.
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Jul 13, 2013 18:53
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Enilev posted:It's not voltage that's causing the beam of electrons to give off radiation. Any changed particle will radiate when accelerated (as when going around a bend). You could send the beam through a plain old permanent magnet to bend it and still get x-rays off. Or crash them into a piece of metal and get bremsstrahlung x-rays, which is how x-ray machines usually work. The frequency is dependent on the energy of the beam for a given bending magnet, thus why we need a high-energy beam. The fun part of it is that you can send the beam repeatedly through klystron-driven cavities, accelerating it more each time. Thus, we get electrons with an energy equivalent to current flowing across a multi-GV potential. However, I now do have more sympathy for the HV power supply folks who had something go pear-shaped during my most recent beam time, which caused a beam dump and a few hours extra for lunch. Three-Phase posted:I noticed that there are warnings about hi-pot testing vacuum contact bottles. If you apply a high voltage to them, they will emit x-rays. That would be due to the bremsstrahlung mentioned above. If you get electron emission from the negative terminal, the electrons will be accelerated to the positive side where they slam into it and are vigorously decelerated and in the process emit x-rays. You can get similar emission from things like vacuum arc-furnaces and even some types of vacuum-tube electronics.
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Jul 14, 2013 19:58
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some texas redneck posted:Working in a restaurant with wimpy 3 phase (120/208/277, no 480 available as it sits) What controls the gas flow to the ovens? You could wire a normally-open relay to the oven supply such that it only gets power if the fan is energized. However, if the gas flow is some manual valve, you've gone from having the ovens on to flooding the place with gas. Welcome to explosion-town.
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Mar 11, 2014 19:15
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Suppose you have a wire that goes from one side of your generator to the other side. As expected, current flows. I come along and cut the wire, now no current flows. If it then attach each end of the cut to a pair of big flat plates that are separated from each other by a small gap, then current flows until the voltage cannot build up more charge on the plates. It is a capacitor. If the generator is producing AC at a frequency where the voltage reverses before the capacitor is fully charged, current will flow as though the wire were unbroken (there is some difference concerning the relative timing of current and voltage changes that are being deliberately ignored, but current does flow). If the wires are long enough, you don't need plates because the wires themselves have enough capacitance.
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Aug 16, 2014 21:30
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wolrah posted:If I did my math right that's 732 lb-ft of torque at the 2500 RPM peak power point. At that level of torque and power/weight, with a flywheel for energy storage, you're in electric dragster territory.
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Apr 30, 2015 17:38
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