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Frozen Horse posted:Could we do that in a way that produces less light pollution? I've seen where some people are pushing for modern streetlights (including LED lights) that generate less light pollution. I think there are some additional environmental benefits, like not messing with migrating birds at night. Bearings - I've heard several stories about where a power plant experienced a severe power failure and completely shut-down. One thing that was lost in this power failure was lubrication oil to the bearings. So as the massive turbines spun down, they generated tremendous amounts of friction in the bearings, getting so hot they welded in place and had to be jackhammered apart. Not fun when you're talking about a 1000MW turbine.
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Sep 17, 2011 02:12
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Three-Phase posted:Bearings - I've heard several stories about where a power plant experienced a severe power failure and completely shut-down. One thing that was lost in this power failure was lubrication oil to the bearings. So as the massive turbines spun down, they generated tremendous amounts of friction in the bearings, getting so hot they welded in place and had to be jackhammered apart. Not fun when you're talking about a 1000MW turbine. There have been quite a few bearings over the years saved by the EBOP (emergency back up oil pump) The main pumps run directly off the turbine shaft but dont really provide enough lubrication at low rpm. We test our EBOPs every outage, they are large DC motors that are connected directly to class 2 station batteries without any protective relaying. I would be far more concerned with a loss of generator hydrogen seal oil than wiping a few bearings. Loss of lube oil means replacing all of the bearing material but a loss of seal oil means you suddenly have pressurized hydrogen gas spilling out into the turbine hall.
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Sep 17, 2011 02:47
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When people talk about hydrogen loss in a generator and say so-and-so number of cubic meters per day or a total hydrogen charge of so-and-so cubic meters, do they mean STP or actual cubic meters? Because, I heard some pretty big numbers...
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Sep 17, 2011 17:19
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Where is this hydrogen coming from?
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Sep 18, 2011 00:29
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Water vapor or actual water being subjected to strong currents.
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Sep 18, 2011 00:43
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squeakygeek posted:Where is this hydrogen coming from? AGA, you putz.
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Sep 18, 2011 02:01
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Some Guy From NY posted:Compare that breaker to a modern 345KV breaker: Great thread. I'm a physicist and we use some equipment that runs on 408V, or three phase 210V, also a coworker is currently designing an experiment that will use like 12kV and 200A. But you guys work with way crazier poo poo than that. I have two questions: 1. Why are the arms in this picture ribbed? 2. Tell me about 3 phase power? 3. Bonus question! What kind of connectors do you use, are there some standard quick release/connect that work for your loads?
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Sep 18, 2011 02:24
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modig posted:Great thread. I'm a physicist and we use some equipment that runs on 408V, or three phase 210V, also a coworker is currently designing an experiment that will use like 12kV and 200A. But you guys work with way crazier poo poo than that. I have two questions: They are "ribbed" so if theres dirt/carbon buildup current doesnt "track" aka flow over the outside causing a fault. By "ribbing" it it allows much more time for a buildup of contaminents and also increases the distance/surface area by up to 600%. This combined with the exterior coating of the material and the angled surfaces helps prevent short circuits/earth faults in the hv switchgear.
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Sep 18, 2011 04:17
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Aliass posted:They are "ribbed" so if theres dirt/carbon buildup current doesnt "track" aka flow over the outside causing a fault. By "ribbing" it it allows much more time for a buildup of contaminents and also increases the distance/surface area by up to 600%. This combined with the exterior coating of the material and the angled surfaces helps prevent short circuits/earth faults in the hv switchgear.
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Sep 18, 2011 13:15
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grover posted:I always understood it to be more related to water; that a solid conductor would be apt to get long streams of water, whereas the ribs break up the streamlet of water into drops and reduce the risk of corona discharge. I think its a little of both tbh. Alot of people don't realise just how well high voltage can track till they have played around with a 33kv Insulation resistance Tester (aka megga) some leads and a dirty floor.
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Sep 18, 2011 14:20
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squeakygeek posted:Where is this hydrogen coming from? Large generators require lots of cooling. The Stator windings can be cooled directly by pumping highly purified water through channels in the windings. 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. Here is Ge's blurb on why they use hydrogen. http://www.ge-energy.com/products_and_services/products/generators/hydrogen_cooled_generator.jsp As for total charges Groda I have never really had to deal with that so I cant tell you if it is STP or not. Normally the gas pressure is between 30 and 75 psi.
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Sep 18, 2011 14:25
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Aliass posted:They are "ribbed" so if theres dirt/carbon buildup current doesnt "track" aka flow over the outside causing a fault. By "ribbing" it it allows much more time for a buildup of contaminents and also increases the distance/surface area by up to 600%. This combined with the exterior coating of the material and the angled surfaces helps prevent short circuits/earth faults in the hv switchgear. Cool, thanks.
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Sep 18, 2011 16:04
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modig posted:2. Tell me about 3 phase power? With three phase power, you have three power lines, and on each the voltage is a sinewave. Each wave is 120 degrees out of phase. So one phase is at 0 degrees, another at 120 degrees, and another at 240 degrees. There are Delta and Wye systems. With a delta, you can connect loads between each of the phases. With Wye, you connect from one of the phases to a neutral. With Wye systems you'll see two voltages, line to line and line to neutral, such as: 120/208 277/480 347/600 quote:3. Bonus question! What kind of connectors do you use, are there some standard quick release/connect that work for your loads? We don't really use connectors for that combination of voltage and power. There are twist-lock and specialized plugs for up to around 100A and 600V. At that point it gets dangerous to disconnect them from the load. Some have locking mechanisms where the plug cannot be pulled unless the outlet is switched off. At high currents and voltages, a cable that could be released would result in an arc flash, and probably result in the fiery death of the person who pulled the plug (if they're lucky.) Let's say I have a 5000HP synchronous motor that needs 300A at 7200V. What I'll do is run a massive triplex cable (three phases in one package) from the motor to the switchgear. The cable bundle is about 4" in diameter. You need to plan this carefully since you cannot turn this cable on-a-dime, a 90 degree turn may require a six foot bend radius. After shutting down the switchgear, and lockout/tagout of course, you open up the back. There are copper or aluminum busbars back there from the breaker serving the load. You use a hydraulic crimper to attach lugs to each of the three phases on the cable after stripping back the outer insulation and inner insulation for the cables, and bolt them onto the appropriate busbars. (You need to watch phasing, which cable is hooked to which busbar, or the motor will spin in the wrong direction, very bad for some loads!) You also may typically apply some kind of electrical grease to the connections to prevent corrosion and overheating. The bolts are torqued using a torque wrench to a specific foot-pound rating. Then, you take a special type of electrical tape, it's like normal electrical tape but spongier and thicker. You wrap this tightly around the entire connection. Then you take another type of electrical tape and cover it again. You do this for each of the splices. Doing this well is a bit of an art, but it's sometimes crucial for protecting the connection. Depending on the location/application, they may omit the taping. Sometimes you don't want to tape if you plan on reversing the motor direction (by swapping two of the phases) in the future. Then, you need to make sure the ground cables inside the main triplex cable are properly grounded at the switchgear. The biggest reason for this is safety, in case the cable is cut. Don't laugh, I've heard of an incident where someone sawzalled into a live 2400V cable, the grounding sheath and our circuit breaker relaying saved his life. Then you do the same thing at the motor. For a big motor, there's a connection compartment. (On really small 1-100HP motors, they're called "peckerheads" but that term is falling out of favor.) Once you're connected, you may want to megger the cable to make sure there isn't any leakage to ground. modig posted:a coworker is currently designing an experiment that will use like 12kV and 200A. That's still a hell of a lot of power, and very dangerous. They're taking a lot of safety precautions, right? Three-Phase fucked around with this message at 01:56 on Sep 19, 2011 |
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Sep 19, 2011 01:45
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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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ANIME AKBAR posted: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. By keeping oxygen out. quote: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? Apparently the viscosity of water can be a problem around moving parts.
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Sep 19, 2011 05:28
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squeakygeek posted:By keeping oxygen out. And it's conductivity....
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Sep 19, 2011 07:24
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Nerobro posted:And it's conductivity.... When conductivity is the problem I think they use mineral oil.
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Sep 19, 2011 08:59
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Nerobro posted:And it's conductivity.... Pureified water is a very poor conductor. Most generators have the stator cooled directly by water. By directly I mean they pump it through channels cut into the copper buss bars which are running around 24kv.
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Sep 19, 2011 11:21
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Pretty much wrong on all counts fellas. (at least with motors) Proper commutation in a dc motor produces NO sparking at all. If there is sparking, something is drastically wrong! Normally its a bad connection, underloading or incorrect brush grade. However dc motors are almost never used for pumping as its not only more expensive to run/maintain its a complete waste as 3phase ac will do the job just fine. (at least for pumping water/oil/tar/slurry. As for closed circuit hydrogen cooling , you have to understand that you have different types of enclosures and different heat ratings for winding insulations. There are motors designed to run at 260degrees C (i have a pair on my workbench at the moment) When you have a totally enclosed motor the only thing thats cooling it is either an extieror fan and/or a interior fan. The exterior one blows air over the stator fins thus helping to cool, the interior ones normally don't do much good unless theres a heat exchanger. However they still function but run a little hotter which is why people will often upsize the ac motor to prevent as much heat being generated. When you have a closed circuit hydrogen system the internal fan just circulates the hydrogen through air to water heat exchanger or air to air (most common) to increase the effectiveness of the system. This really isnt a problem as unless theres a pretty drastic fault in the windings theres NEVER any sparking inside these motors and a pure hydrogen environment means theres no flames. For it to explode you would have to have something amazing happen like the internal fan shattering into the windings and cracking the endsheild. When a motor is water cooled (relativly rare) unless its a pump the rotor never touches the water , pumping it would add way to much load to the motor. As is with a fan if you replace it with one designed for a slower speed motor you can overload it / induce premature failure. So, Basically the stator is designed so instead of the back iron being one soild unit, its much thicker and has a bunch of tubes through the entire length of it allowing water to circulate. There is no need to immerse the windings as copper > iron>iron > water is a fairly effective method of transferring heat. Like Transformers the water can either be circulated with convection or forced with a secondary pump (fairly uncommon for stuff under the 10megawatt range) I have never seen nor heard of a motor being cooled with mineral oil , that would not only be worse then water it would cost more. Perhaps you were thinking of transformers (which are often immeresed in oil). "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" 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.
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Sep 19, 2011 11:25
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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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ANIME AKBAR posted:I'm talking about something a bunch of PhD chem students rigged up without supervision. I'm pretty sure jobs were lost over it. Gotta love people playing with electricity. Many a smart person has got a belt from tinkering around with stuff they shouldnt have.
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Sep 19, 2011 13:28
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Three-Phase 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.
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Sep 19, 2011 16:19
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Before I go into this to far, I have never seen a motor cooled by imersion in a fluid. H2 cooling seems perfectly sane, as does air. As does running cooling fluids through the stator. I have heard of rotors having slip rings and cooling water too.squeakygeek posted:When conductivity is the problem I think they use mineral oil. Which looses the benefits of waters high specific heat. helno posted:Pureified water is a very poor conductor. Water inside a motor casing, interacting with commutators, brushes, and windings, isn't going to stay pure long. And "poor" at 3kv is still "holyshitlotsofpower." Running cooling water through the stator seems perfectly sane to me. You're not depending on the water being an insulator, so go for it.
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Sep 19, 2011 17:07
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Doesn't hydrogen gas have a tendency to be absorbed into metals and make them brittle? Or is that only at very high pressures?
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Sep 19, 2011 20:45
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DuckConference posted:Doesn't hydrogen gas have a tendency to be absorbed into metals and make them brittle? Or is that only at very high pressures? Im not sure about that , but i will say its never been a problem for me. Bad casting on internal fans/balance weights on rotors are much more likely to cause premature failure.
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Sep 19, 2011 21:54
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Nerobro posted:Water inside a motor casing, interacting with commutators, brushes, and windings, isn't going to stay pure long. And "poor" at 3kv is still "holyshitlotsofpower." Yeah we keep those things separate for a reason. The water is continously being demineralized as it is circulated. Slip rings and brushes are in an external enclosure and we check for hydrogen leakage on a weekly basis. The leakage current in the stator water system is down in the mA even at 24kV.
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Sep 19, 2011 22:52
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Talking about water - I saw a video of how bird crap is cleaned off large insulators - they have a pressure washer on a helicopter, and the washer uses pure, distilled water. . Some of the large motors I've worked with (>5000HP) either have a large internal fan, or a "top hat" assembly with one or two blowers. If the blowers fail or there's a problem with the motor, the protective relay keeps an eye on the RTDs (thermometers) embedded within the stator. The relay also sends the hottest temperature value as a 4-20mA DC signal (such as 4mA = 0C and 20mA = 300C) to a SCADA system. If the motor's temperature begins to approach the thermal damage curve of the motor, the relay trips the motor. Sometimes the SCADA system can also send a signal to trip the motor if it doesn't like what it's seeing. In a well designed system, the SCADA system should give the operators multiple levels of alarms. Such as: (these temperatures are approximations) BAD VALUE - signal is over or under the 4-20mA range, usually means a wire is broken LOW TRIP - temperature is too low to operate the motor (this is probably rare) LOW ALARM - highest stator temperature is unexpectedly low, like under 10C HIGH ALARM LEVEL 1 (High) - highest stator temperature is over 125C, the operators should look into this or at least keep an eye on it HIGH ALARM LEVEL 2 (High-High) - highest stator temperature is over 150C the operator must ACT RIGHT NOW to find why the temperature is going up and correct it, or gracefully bring the machine offline HIGH TRIP- highest temperature is over 175C, the SCADA system has caused the motor to trip, assuming the protective relay didn't already bring it down. This is the point where people start getting really angry phone calls from engineers at the plant. Possibly with shouting matches and getting in people's faces, depending on the plant and if the device that went down is costing the company significant money for each minute it's offline. (I've been told this high-stress bad behavior is a fairly common phenomena in the automotive industry.) My understanding is that tripping poses additional dangers when you trip a generator. Those are: 1. The excitation of a synchronous generator must immediately be stopped and the field discharge resistor inserted into the field circuit to prevent a catastrophic buildup of excessive voltage on the stator 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. Three-Phase fucked around with this message at 01:49 on Sep 20, 2011 |
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Sep 20, 2011 01:35
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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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Frozen Horse posted: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. However, it's possible that the condenser pressure rises too quickly (it's not meant to take the rated steam flow for very long at all), dump blocking is enabled, and steam pressure builds in the reactor pressure vessel until one of the reactor pressure relief values is reached. Then, steam is dumped to the suppression pool. As far as the coolant pumps go, there are feedwater/condensate pumps (same thing, as far as a reactor engineer is concerned, since they're in series) controlling flow into the reactor, as well as circulation pumps controlling flow circulating within the reactor through the core. A generator trip will lead to a scram condition of some sort getting fulfilled, and both circulation and feedwater/condensate are intended to be brought down on painstakingly developed ramps (e.g. 100% to 0% in 5 s). These ramps assume continuous external power, even in the case of a generator trip. The plant's pumping systems are designed to consume power just like the farm houses, the gas station and the outage workers' temporary brothel down the road--that is, everything is pretty much business as usual. A dump condition would just result in continued circulation dump->condenser->condensate->feedwater->RPV. If there is a mass imbalance, something will, for example, run into a low tank level condition and kill some pumps or close some valves, just like normal. The real interesting problem is that this event is somewhat hard on the fuel, as the sudden closure of the valves going to the turbine will cause a pressure spike, a void collapse, and a reaction increase. This isn't exactly the kind thing that happens every year, but it's probable enough that the reactor is run with enough margin (think underclocking the reactor) to avoid damaging (overheating) the fuel in the event that such a thing would happen. For the record: In the event that the fuel was damaged by an event of this nature, it usually means that you have to shut down for a week and replace a handful of the several hundred fuel elements. Expensive, but not especially more radioactive than normal.
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Sep 20, 2011 22:01
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Is it correct that the reactor "physics" changes over the life of the fuel? So a reactor with fresh fuel that has more pure uranium will behave differently than a reactor where half of it's uranium has been depleted and replaced with other isotopes and compounds? I'm also assuming the pump ramp-down over five seconds is to reduce the effect of water hammer, right? Three-Phase fucked around with this message at 01:13 on Sep 21, 2011 |
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Sep 21, 2011 01:10
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^^^^ True. See http://en.wikipedia.org/wiki/BurnupThree-Phase posted:1. The excitation of a synchronous generator must immediately be stopped and the field discharge resistor inserted into the field circuit to prevent a catastrophic buildup of excessive voltage on the stator Static exciters can respond incredibly fast to things like this. The field discharge resistor is just a big piece of folded steel and is connected to the DC bus by a poised SCR. So in a trip the main bridges are immediatly stopped the discharge SCR fires and within milliseconds the DC breaker is open. As to reactors response to load rejections we can dump 60% of reactor power directly to the condenser (this corresponds to the same amount of steam energy that normally makes its way to the condenser during normal operation). In the event of loss of grid events we normally keep the reactors and turbines up and island ourselves (which results in a crapload of steam going out the roof). This is why we didn't poison out in 2003.
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Sep 21, 2011 01:19
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helno posted:^^^^ True. See http://en.wikipedia.org/wiki/Burnup Does this depend on the exciter? The older ones I've seen have two routes through the FDR: 1. Through a normally-closed electromechanical contactor 2. Through a crowbar circuit If you don't correctly apply the crowbar circuit (a set of zener diodes that will fire an SCR that's in parallel with the discharge contactor at some voltage between, say, 200VDC and 800VDC), you may still risk flashing the rings. I'll need to check with one of my coworkers for details on the FDR and flashing the slip-rings. (On the slip-rings is an adjustable arc-gap, so if something really bad happens at the exciter, there's a set point for the arc to occur at.)
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Sep 21, 2011 02:13
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My experience with exciters is limted to the rather fancy new ones that we have installed. The old ones had crowbar circuits and a DC contactor that had a million ways to brake your hand while maintaining it. Our slip rings are separated by a large nonconductive duct for the ring cooling air.
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Sep 21, 2011 02:58
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Three-Phase posted:I'm also assuming the pump ramp-down over five seconds is to reduce the effect of water hammer, right? That's one reason to do it, though pumps and fans usually have pretty long ramp times anyway due to high inertia relative to motor power needed. Fans can be especially sensitive, due to the lighter-built ductwork being far easier to damage with sudden changes in flow/direction. One of the fans I'm working on here is ramped at 45 seconds to accel/decel.
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Sep 21, 2011 13:53
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Three-Phase posted:Is it correct that the reactor "physics" changes over the life of the fuel? So a reactor with fresh fuel that has more pure uranium will behave differently than a reactor where half of it's uranium has been depleted and replaced with other isotopes and compounds? Absolutely. Estimating how the fuel will behave one day/month/quarter/etc into the fuel cycle is a large part of the job of core design (you're not just refueling the reactor each year, you're making a whole new machine with different behavior). Your uranium isn't just going to turn into fission products, which are radioactive and (more importantly) generate heat after the reaction is halted, but also new fuel (plutonium), which doesn't behave the same as uranium. The same [BWR] fuel element will have drastically different changes in composition take place at the bottom than at the top. Three-Phase posted:I'm also assuming the pump ramp-down over five seconds is to reduce the effect of water hammer, right? No, but god knows water/steam hammer is on everybody's mind in the design process... (Attention: only BWR) Fundamentally, the feedwater (which goes into the reactor pressure vessel to be turned into steam) can't fill up the tank forever. If you close the steam valves, you've got a tank partially filled with water, partially with steam, which has no outlet. If you know the outlet (i.e. steam valves) are closing, you might as well shut off the flow into the vessel. Water level in the vessel too high? Another good reason to shut off the flow into the tank. The circulation pumps (which move the water around in a loop inside the vessel) ramp down because:
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Sep 21, 2011 22:04
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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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Is it just me, or are BWRs a little "scarier" than PWRs? I just don't like the fact of maintaining a turbine/generator set that has radioactive steam blowing through the turbine, that and the fact that you have bona-fide boiling going on inside the reactor vessel.
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Sep 22, 2011 11:22
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Yeah it never seemed like a great idea. As soon as you have failed fuel your entire system is contaminated with fission products.
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Sep 22, 2011 14:18
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Aliass posted:Im talking from complete cold start. That was the figure i was told but most of ours are pretty old. We normally use gas turbines to deal with the excess demand and only use coal fired power stations to provide the baseload power. How fast a plant can start up is usually determined by how fast you can heat up the system. A boiler is started up very slowly over several days to prevent the refractory from cracking. Depending on how the plant is built there might be an extensive process to bring the whole plant on line. For a steam plant, start-up will put the most stress on your equipment usually. Because of the long start up times companies will generally be reluctant to take a coal plant offline. Three-Phase posted:That sounds similar to US large customers, but the stuff I'm more familiar with is a lot larger than 100kW+, more like 10MW-250MW range. But yeah, there's complicated billing based on peak watts/VARs (I think it's in a sliding 15-minute range) along with total consumption and making sure you don't lag more than, say, 0.95 power factor at any time unless you want to be fined extra. I worked doing O&M for a gold mining company that built a power plant when their long term power contract expired and the power company wanted to renegotiate higher. We had around 118 MW of capacity that was just about enough to cover the companies mines in the state (should have been more than enough but they kept adding more load to the contract). During winter and spring it was easy for our broker to supply cheap power and reduce the plant to minimum generation (the company did not negotiate prices for parasitic load so we had to have 2 engines, 16MW, running at all times to keep from being charged peak rate). During peak season we ran at 100% capacity for as long as possible. Even if the broker was able to find decent spot prices the PowCo frequently cut our imports and made us generate due to a lack of transmission. Each week the mines would predict their generation and send it to the broker who would look for power on the market to cover with a combo of long term contracts and spot prices. If the mines had equipment go down or the PowCo had a problem there was a direct line to their control room on our desk we used to discuss issues with them. They would call every now and then begging for any spare capacity we had as we had start up times of 5 minutes or less usually. They also asked us to adjust our PF once but there was nothing in the contract for that so screw them. Also, the gold mining company had never had a power plant before and did not know how to negotiate a contract leading to things like the PowCo being able to charge peak power prices for any parasitic load we might draw even at off peak times. We could also never go down without spinning reserve for even a minute without the PowCo being able to charge something like peak price for the whole month. On the one time we tripped two of our transformers offline for less than 10 minutes we would have been on the hook for $500k or so (the PowCo engineers told the accountants to gently caress off and not charge us since we gave them any help we could with generation when they called).
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Sep 22, 2011 18:45
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Three-Phase posted:Is it just me, or are BWRs a little "scarier" than PWRs? Radioactivity going into the turbine in a BWR plant has two components:
The irradiated water is massively radioactive, but only while the plant is running. After a matter of minutes after shutdown, it will have decayed into nothing. The other stuff lasts longer, and is closely monitored (see below). PWRs have plenty of scary things to keep track of. For example, a BWR has very simple water chemistry: pure water. Just like any old coal plant boiler... A PWR, on the other hand, is constantly adding and removing boron-bearing acid from its reactor water to control the reaction rate. This can cause problems if done improperly: http://en.wikipedia.org/wiki/Davis-Besse_Nuclear_Power_Station#Reactor_head_hole PWRs separation between systems, the steam generators, consist of thousands upon thousands of small, tightly packed tubes bearing a pressure difference of ca 85 bar. The potential for a leak is big, and so is the time it takes to fix it if you can't just plug the bastard. helno posted:Yeah it never seemed like a great idea. As soon as you have failed fuel your entire system is contaminated with fission products. Yeah, popping a fuel rod will contaminate your turbine -> condenser -> feedwater system, but there are sensors for measuring the radioactivity and (IIRC) radiation alarm signals which can shut down and seal off the reactor from the rest of the plant in a matter of seconds. The radioactivity passing through the turbine and condenser is constantly monitored, and poking a pinhole in just one of the 50,000-100,000 fuel rods in your BWR core can actually be detected and dealt with before things get out of hand. Even though the steam has been passing through it from the core all year long, people can still climb into the turbine housings and work the whole outage without space suits.
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Sep 22, 2011 23:28
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