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For awhile now I've been working at a job that involves a lot of large electrical power systems, and it's given me a lot more knowledge on how electrical power systems work. I was actually thinking about creating a thread about it in GBS, actually being inspired by the popularity of the Anthropogenesis thread. Electrical power generation uses huge, awesome machines. This thread can cover different things pertaining to power systems. Just a few example questions: 1. Why do those power poles carry wires in multiples of three? 2. What are (insert funny looking object in a substation) 3. Have you ever been shocked? 4. How much power actually goes through power lines? 5. How does the grid work? 6. How do power outages occur? 7. How do you turn on and off circuit breakers if the power goes out? Three-Phase fucked around with this message at Nov 07, 2009 around 10:20 |
| # ? Nov 07, 2009 10:17 |
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| # ? Nov 20, 2009 23:07 |
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What's the deal with 'power factor' and 'power factor correction'?
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| # ? Nov 07, 2009 10:26 |
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I'm going to have to take the "Have you ever been shocked?" question. Have you or fellow employees ever been shocked? I've known several people that have been struck by lightning or shocked by electrical systems and have never been quite the same. Extrapolate please?
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| # ? Nov 07, 2009 10:32 |
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What would it take to have replace coal/gas with a wind based power supply? I'm thinking it would require massive amount of storage, so probably rather difficult in most cases, but how feasible would it be for a country with roughly 50000GWH total annual consumption, with plenty of existing hydro electricity (about 50%-60% of the 50000GWH depending on weather) and the possibility to easily build a pumped storage facility with about 10000GWH storage capacity?
FlyingDodo fucked around with this message at Nov 07, 2009 around 10:42 |
| # ? Nov 07, 2009 10:39 |
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Calast posted:What's the deal with 'power factor' and 'power factor correction'? Well, I wrote a five-paragraph post explaining it, but my browser crapped itself. FML. Anyhow, you're going to now get a one-paragraph explanation: A load with a poor power factor (more reactive than real power) draws more electrical current to do X amount of work than a load with a good power factor (more real power than reactive power). Resistive loads draw real power, while capacitive and inductive loads (like induction motors and induction heaters for lagging, capacitive loads like power supplies for leading) draw reactive ("fake") power in an AC circuit. Having a poor power factor loads is more expensive for the utility company. They will bill a large customer with a high voltage connection, like a factory, much more if they have a poor power factor. Power factor correction usually acts as capacitor banks that are switched in to cancel out in induction from devices like large motors. This saves money, but I've seen where switching the banks in can create a voltage spike that can resonate briefly through an entire power system. It has to be done carefully. Also, synchronous motors (essentially motors that can act as either motors or generators very easily) can be run at whatever power factor the operator chooses. So what a plant operator can do is remove the load and run the motor unloaded, and crank the power factor leading to cancel out the effect of other lagging equipment. That's also called a "synchronous condenser" (condenser being the silly British name for capacitor). If played right, on hot summer days where millions of air conditioners are running, power companies might call up big factories and plants and essentially say "FOR GOD'S SAKE PLEASE WE NEED VARS PLEASE SWITCH IN YOUR CAPACITOR BANKS AND SYNCHRONOUS CONDENSORS PLEASE PLEASE PLEASE!" That's where the power company can start paying the customer to utilize their equipment to keep the power grid stable.
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| # ? Nov 07, 2009 13:40 |
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How do generators on the grid stay synchronized? Is it a stable system? As far as I'm concerned, power plants were built to generate steam, with electricity as a by-product.
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| # ? Nov 07, 2009 13:40 |
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I'm double posting - no way in hell am I explaining PF again. (Edit, beaten by Groda!)Catsoup posted:I'm going to have to take the "Have you ever been shocked?" question. Have you or fellow employees ever been shocked? I've known several people that have been struck by lightning or shocked by electrical systems and have never been quite the same. Extrapolate please? I was shocked from a 75V variable supply. A friend of mine was hit with 480V (480V/277V is a very common industrial voltage for motors and machines) directly across the chest. CPR saved his life. Some "small equipment" in plants go as high as 600V/377V, above that and equipment gets classified as "high voltage" (safety standpoint) or "medium voltage" (equipment standpoint). I've seen equipment that's run off 2400V, 4160V, 6900V, and 13800V. Above that and you get to voltages that the machines themselves don't used, it's just for moving around power (approx. 32kV, 138kv, etc.) if you contact something of that high voltage, it's not as much of a shock. It's more of an "all the water in your body will turn to steam" and you'll kind of blow up. Here's a little video about what live 600/347V systems can do. It's safe to say that 480V/277V systems are equally dangerous: http://www.youtube.com/watch?v=VSrpc8nxnHM Some people do live installation from 120V to 600V. Where I work, doing hot installation work is absolutely forbidden and would probably cause a person to get shitcanned if caught. Live work kills people. It's not just shock on big systems, there's also arc flash. Shock hopefully just injures or kills. Arc flash is where you're burned to death. Unless you're wearing a flash suit. http://www.youtube.com/watch?v=8hO1s_SFHe0 (Caution - there is a graphic video clip of an incident in the middle of this video.) When you have an arc flash, it's like standing a few feet from the surface of the sun. Solid copper vaporizes. Clothing can melt and fuse to skin. I've heard numbers thrown around like 3-rd degree burns over 90% of the body. More details on this stuff later. Three-Phase fucked around with this message at Nov 07, 2009 around 14:08 |
| # ? Nov 07, 2009 13:48 |
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Groda posted:How do generators on the grid stay synchronized? Is it a stable system? It's tricky, but not as difficult as you think. As far as stability is concerned, that's also a challenge, but with proper engineering and protection systems, there are ways to protect and stabilize the system. If it's done wrong, you can do goofy things like having generator A feed into generator B, or have generator A and B "fight" back and forth with one another, causing the system to oscillate as they pass load back and forth. It's not easy. This stuff requires very good mathematical and control systems knowledge. - - - - - To synchronize a generator to a bus (a bus is where multiple electrical devices tie into) you need to be match the bus' voltage, frequency, and phase. In the old days, this was done essentially by hand - with a guy watching meters and synchroscopes. Nowadays that is done electronically. Typically you'd get the voltage and frequency synchronized first. Then you get the phase matched. At that point, the motor is synchronized, but not connected, to the line. After it's synchronized, a big circuit breaker closes to connect the motor to the bus (either directly or via a transformer). Now, for the transformer to start putting out power, the phase is shifted just a little bit. That allows the transformer to supply current. Of course, as that transformer starts to take the load, load is being removed from other transformers. If you think about it, the more machines you have on a single grid or bus, it should inherently be more stable, as bringing on one generator at a time means less of a sudden change to the entire system. Now let's say something goes really south. Like the exciter for the generator (assuming a big synchronous generator like at a hydro plant) dies. Or the generator starts to overheat, or a short circuit occurs in the stator windings. What you have is a protection relay. These used to be mechanical, but now there's electronic, like little computers. That relay says "holy smokes, something is really wrong with the generator (or motor, or bus, or transformer) and I'd better do something!" So in the case of the generator, it sends a signal to the circuit breaker to trip. That takes the generator off the bus. The important part is now the generator is open-circuited. If the exciter is running, it has to shut down RIGHT F'ING NOW or bad things will happen. However the exciter can monitor the status of the breaker so that if it trips, it stops applying excitation. Three-Phase fucked around with this message at Nov 07, 2009 around 14:00 |
| # ? Nov 07, 2009 13:56 |
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FlyingDodo posted:What would it take to have replace coal/gas with a wind based power supply? I'm thinking it would require massive amount of storage, so probably rather difficult in most cases, but how feasible would it be for a country with roughly 50000GWH total annual consumption, with plenty of existing hydro electricity (about 50%-60% of the 50000GWH depending on weather) and the possibility to easily build a pumped storage facility with about 10000GWH storage capacity? I'm not sure, I'm really not. Aren't there a lot of efficiency losses (head loss, etc.) with pumped storage? That and I don't think it's that simple to build. Storing power - putting the genie back in the bottle - is still a challenge. I think Canada has a tremendous hydro capacity, and they have some big plants in places like Quebec where they generate the electricity, step it up to ultra-high voltage, and move it to places like Toronto. The US could probably do some wheeling-and-dealing to build hydro plants and have Canada supply us clean power from them, but it would involve a lot of new energy infrastructure. With renewable energy we'd need a better grid as well - so we can take power from where it's plentiful and move it to where it's needed. The current US power grid isn't in really hot shape. Some utilities use renewable but then have dozens of medium-voltage (4160V) generators in trailers for use when the environmental conditions aren't right or the load is really high, like on a breezeless, hot summer day. - - - - - - Personally, I'd love to see more wind farms supplying clean energy. They're a really beautiful sight to behold. I've also stood underneath operating Vestas units - you can talk to someone in a whisper right under the unit. They're about as quiet as quiet gets. I honestly think the "wind turbines are really loud" people have some sort of severe mental illness. (I'd like to say, "well, you didn't like the noise. We listed. We're now installing the coal-o-matic 9000 power plant across the road instead. Enjoy!") http://www.youtube.com/watch?v=pTkBKkkczD0 Some of those blades are as long as a football field. Three-Phase fucked around with this message at Nov 07, 2009 around 14:24 |
| # ? Nov 07, 2009 14:12 |
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I think the main issue with some renewables such as wind, solar etc is that of availability. You can't just turn on a big coal fired plant at the drop of a hat, it takes a while, so you can't rely on them being ready to take up the slack when the wind/sun drops. So for the OP: You got a 3-phase sync machine operating as a generator, driving a 50MW load. The assembly that holds the rotor in place is ancient, heavily fatigued and suffers from weird vibrations nobody can identify. There's a short circuit fault across all 3 phases between the machine and the load and the excitation remains unchanged because the software interlock was written by an unpaid intern an never checked. What's like likely outcome? Also, I was talking to somebody yesterday who suggested there was a hard theoretical limit on the efficiency of power plants using any kind of heat engine, dependent on the difference in temperature between the hot and cold side (like a coal fired plant with a steam turbine or whatever). What's the typical efficiency of such power plants? (I have no idea, but I'd assume it was 25% or something like that)
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| # ? Nov 07, 2009 15:49 |
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Kippling posted:Also, I was talking to somebody yesterday who suggested there was a hard theoretical limit on the efficiency of power plants using any kind of heat engine, dependent on the difference in temperature between the hot and cold side (like a coal fired plant with a steam turbine or whatever). What's the typical efficiency of such power plants? (I have no idea, but I'd assume it was 25% or something like that) Yeah, it's the carnot limit. http://en.wikipedia.org/wiki/Carnot...thermodynamics) People typically expect coal to have an efficiency in the 30-40%, with most ending up at the lower end of the spectrum.
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| # ? Nov 07, 2009 19:23 |
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Kippling posted:I think the main issue with some renewables such as wind, solar etc is that of availability. You can't just turn on a big coal fired plant at the drop of a hat, it takes a while, so you can't rely on them being ready to take up the slack when the wind/sun drops. your logic is backwards. Coal plans can't run at the drop of a hat, but you can run them at low 'minimum stable' levels, and ramp them quickly after the fact. Not that it's great for them, most coal units weren't designed to ramp all over all the time. Your replacement power for wind would have to come from some sort of fast ramp - Hydro or thermal (nat gas and potentially coal). You can build extremely fast ramping natural gas plants (cold start to full power (100MW) in 10 minutes). Problem is they're generally simple cycle and just not as efficient as other types of generation, so they can be pricey to run. I do some of the real time power trading stuff for a deregulated market, so guys like three-phase are supplying my bread and butter! Three-phase, you explained sync cond much better than I did when I was asked last week.
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| # ? Nov 07, 2009 19:24 |
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^ Yeah! Synchronous condensers are way cool. With a good SCADA (supervisory control and data acquisition system) controlling the exciter, you can tell it "hey, run with a power factor of 0.9 leading" and use the SCADA system as a sort of "cruise control" for power factor correction. Again, the thing with synchronous condensers are that you can decouple almost any synchronous motor and make it a condenser. That and you can gently apply correction, instead of slamming in capacitor banks and creating spikes through the system. Also, I believe that it's not a good idea of running it past around 0.8 leading. I believe you can get stability issues as well as higher than expected voltages in the system. I need to confirm that. Kippling posted:You got a 3-phase sync machine operating as a generator, driving a 50MW load. The assembly that holds the rotor in place is ancient, heavily fatigued and suffers from weird vibrations nobody can identify. There's a short circuit fault across all 3 phases between the machine and the load and the excitation remains unchanged because the software interlock was written by an unpaid intern an never checked. What's like likely outcome? Interesting question! Can you clarify a few things? First, I don't like the whole "wierd vibrations that nobody can identify" comment. Have the vibrations been measured and quantified? Have they been changing or increasing in amplitude? I'm not a machine vibration expert, but on a big machine like yours there should be sensors to look at shaft position and vibration. Second, is there any sort of protection relay for the generator, or are we talking about a hypothetical/ideal situation where there's a perfect three-phase fault with very low impedance, and this fault occurs close to the windings of the motor? Also, when you say "the load remains unchanged", you're talking about the prime mover of the generator, right? (This thing smells a little bit like a big motor-generator setup for a large variable speed system.) I think it's unlikely for a perfect three-phase fault (where all the phases fault) to occur right before there's any protection - a relay would see a voltage/current imbalance and need to kill the exciter and the prime mover. I would think for a 50MW machine you'd have some form of protection relay that would send a signal to kill the excitation and the prime mover. The short circuit will do some interesting things - overheating/melting components, fire, and big magnetic fields that could pull things apart. That can be calculated by looking at the transient and sub-transient reactance of the generator. That and the way the exciter works could also limit the fault. This is all more speculation than experience - generation systems are an area where I haven't had that much experience I'm afraid. Bottom line is you need to kill the exciter and the prime mover. What would be bad as well is if the generator open-circuits rather than short circuits. I believe this will cause a nasty voltage surge. Three-Phase fucked around with this message at Nov 07, 2009 around 20:55 |
| # ? Nov 07, 2009 20:41 |
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Northern posted:Coal plans can't run at the drop of a hat, but you can run them at low 'minimum stable' levels, and ramp them quickly after the fact. When a plant is running as a backup at a minimum stable level, roughly what is the difference in operating costs and fuel usage, compared to when it is running in a regular fashion? Is keeping a running backup to support renewables fairly common? Just curious =) I'm learning here.
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| # ? Nov 07, 2009 20:48 |
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Northern posted:your logic is backwards. Coal plans can't run at the drop of a hat, but you can run them at low 'minimum stable' levels, and ramp them quickly after the fact. Not that it's great for them, most coal units weren't designed to ramp all over all the time. What about small "peaking" units to provide temporary power while you crank up additional generation? Northern posted:Your replacement power for wind would have to come from some sort of fast ramp - Hydro or thermal (nat gas and potentially coal). You can build extremely fast ramping natural gas plants (cold start to full power (100MW) in 10 minutes). Problem is they're generally simple cycle and just not as efficient as other types of generation, so they can be pricey to run. Yeah, I've seen natural gas generators used as peaking units. I could imagine a large plant using them to offset costs if they need to use a lot of power during prime-time, like from 8AM to 8PM when electricity is expensive, especially if it has to be purchased in MWH blocks beforehand. Kippling posted:When a plant is running as a backup at a minimum stable level, roughly what is the difference in operating costs and fuel usage, compared to when it is running in a regular fashion? Is keeping a running backup to support renewables fairly common? Well, for a fossil fuel plant, I'm assuming the resource cost is lessened - it's like a pilot light in your oven. The problem comes when you have to pay to staff three shifts of personnel while you aren't pumping out power. There's a certain break-even economic point where you're making money. If something takes down your generation, like a transformer catching fire in the switchyard, you're loosing money for every second you're down. That's pure loss - putting out 0MVA means taking in $0. And getting an additional generator online isn't like flipping a switch. Well, it sort of is with SCADA systems, but you need to take time to check out the system, make sure you've got all the ancillary stuff online like cooling and lubrication, bring the device up to speed, sync in, and then shift the phase to start pumping out current. That takes a bit of time and requires skilled and knowledgeable technicians and operators. Three-Phase fucked around with this message at Nov 07, 2009 around 21:03 |
| # ? Nov 07, 2009 20:56 |
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Three-Phase posted:Interesting question! Can you clarify a few things? I'll try! I'm making this up as I go along. Three-Phase posted:First, I don't like the whole "wierd vibrations that nobody can identify" comment. Have the vibrations been measured and quantified? Have they been changing or increasing in amplitude? I'm not a machine vibration expert, but on a big machine like yours there should be sensors to look at shaft position and vibration. Lets say there is some condition monitoring/health management/diagnostic software that's looking for unusual frequency content in a particular sensor that picks up vibrations. It triggered a warning that something unusual is going on, but it doesn't correlate with any expected failures, but could be a sign of an incipient problem or fatigue. Three-Phase posted:Second, is there any sort of protection relay for the generator, or are we talking about a hypothetical/ideal situation where there's a perfect three-phase fault with very low impedance, and this fault occurs close to the windings of the motor? Lets say the impedance between the first and second/third phases is relatively high compared to the impedance between the second and third phase, which could be considered near zero. So it's not balanced. Three-Phase posted:Also, when you say "the load remains unchanged", you're talking about the prime mover of the generator, right? (This thing smells a little bit like a big motor-generator setup for a large variable speed system.) I could have taken a bit more care when writing that! But yeah, you know what I mean. Basically the exciter & prime mover remain unchanged. Three-Phase posted:I think it's unlikely for a perfect three-phase fault (where all the phases fault) to occur right before there's any protection - a relay would see a voltage/current imbalance and need to kill the exciter and the prime mover. I would think for a 50MW machine you'd have some form of protection relay that would send a signal to kill the excitation and the prime mover. Lets pretend we're working at a place that builds sync machines, and this has occurred during a test of a new design that hasn't yet had any protection/safety systems installed (apart from the condition monitoring thing I alluded to before... drat). Three-Phase posted:The short circuit will do some interesting things - overheating/melting components, fire, and big magnetic fields that could pull things apart. That can be calculated by looking at the transient and sub-transient reactance of the generator. That and the way the exciter works could also limit the fault. That sounds pretty rough too. I'm basically just interested in what happens when these big machines fail. I was only ever taught what they're supposed to do in normal conditions, and I've never had anything to do with them aside from that (but potentially will in the future). If this is silly, feel free to opt-out =) I'm just playing word games Kippling fucked around with this message at Nov 07, 2009 around 21:18 |
| # ? Nov 07, 2009 21:15 |
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Kippling posted:That sounds pretty rough too. I'm basically just interested in what happens when these big machines fail. I was only ever taught what they're supposed to do in normal conditions, and I've never had anything to do with them aside from that (but potentially will in the future). They do stuff like throw huge brushes a few miles.
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| # ? Nov 07, 2009 21:18 |
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Three-Phase posted:To synchronize a generator to a bus (a bus is where multiple electrical devices tie into) you need to be match the bus' voltage, frequency, and phase. In the old days, this was done essentially by hand - with a guy watching meters and synchroscopes. Nowadays that is done electronically. Heh... I was operating two 200 kW generators in parallel for the TV compound at a car race. They're equipped with these guys- http://eps.woodward.com/eps_uk/prod...ntrols/gcp-31-2 and all was well. Paralleling is a simple matter of making sure the GCPs are talking and then mashing the "breaker on" button. They then talk, fiddle, adjust, and *click*WHIRRRRRRRRR*click* the breaker closes. Anyway, the rotating diode assembly in one generator shat itself. Not a huge problem normally, as the GCP should detect reverse current and shunt open the breaker, but it didn't. Someone had gone in there and disabled the reverse current safety. I watched in horror as the current on both generators built higher and higher and higher, not knowing which one to shut off. I was just about to drop one, figuring I had a 50-50 shot at guessing right, when the breaker on the failed unit* popped on overcurrent. The good one kept on going and I didn't drop the load. That was the beginning of a very bad day. *I would have shut down the good unit had this not happened. 
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| # ? Nov 07, 2009 21:46 |
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How do you feel about "smart grids" and implementing that kind of technology?
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| # ? Nov 07, 2009 22:06 |
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EvilDonald posted:Anyway, the rotating diode assembly in one generator shat itself. Not a huge problem normally, as the GCP should detect reverse current and shunt open the breaker, but it didn't. BRUSHLESS EXCITERS!!!   Kippling posted:Lets pretend we're working at a place that builds sync machines, and this has occurred during a test of a new design that hasn't yet had any protection/safety systems installed (apart from the condition monitoring thing I alluded to before... drat). You're kidding, right? No protection relay or hard-wired protection system? E-stop for the exciter and prime mover? Whatever your company is testing, PLEASE set up a good camera and record this. And know where the nearest exits in your building are. Also, is it possible there's, like, a stupidly severe imbalance with the shaft? Are you measuring the impedances with the shaft in the motor or not? I'm just thinking if there was a bigger air gap and a really bad imbalance or misalignment, it would cause the measured impedances to be out of whack... Insurrectum posted:How do you feel about "smart grids" and implementing that kind of technology? It's great until someone hacks in at a plant or a substation and does things like trip or close breakers, change trip curves and settings, or does other nefarious things. Security has to be as airtight as possible. Three-Phase fucked around with this message at Nov 07, 2009 around 22:24 |
| # ? Nov 07, 2009 22:18 |
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For a layman, what is an exciter? Also, I assume some of what you're talking about is failure of these systems and it sounds like bad things would happen, so what would I see if I were physically in the same room or near one of these systems, or what would happen in general during any kind of these failures?
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| # ? Nov 07, 2009 22:21 |
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Three-Phase posted:It's great until someone hacks in at a plant or a substation and does things like trip or close breakers, change trip curves and settings, or does other nefarious things. Security has to be as airtight as possible. What kind of damage could people actually do if they managed to get into where these things are controlled and then mess with the settings?
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| # ? Nov 07, 2009 22:24 |
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Insurrectum posted:What kind of damage could people actually do if they managed to get into where these things are controlled and then mess with the settings? You could destroy equipment! Releasing the brown smoke, that sort of thing. Ibsen posted:For a layman, what is an exciter? Also, I assume some of what you're talking about is failure of these systems and it sounds like bad things would happen, so what would I see if I were physically in the same room or near one of these systems, or what would happen in general during any kind of these failures? So in a motor you have two parts, a rotor and a stator. The rotor rotates inside (duh) and the stator is the ring on the outside. The exciter generates a DC current that flows into the rotor windings. This basically makes a big electromagnet. There is also a rotating magnetic field generated by the stator coils. This rotating field "catches" the constant magnetic field created by the rotor (via the exciter), and causes the motor to turn. Assuming no slip, the synchronous motor will rotate based on the frequency of the incoming line and the number of poles on the stator. Speed (RPM) = (frequency * 120)/poles So for a four-pole machine operating off a 60hz line, you get 1800 RPM. (A common speed.) Big generators, like in hydroelectric plants, would spin slower but have more poles to generate 60hz voltage. For instance a 24-pole machine would need to spin at only 300 RPM to generate 60hz. On a motor, if the exciter fails, you'd see a drop in the stator current, and the motor would slow down. One important item is a field discharge resistor. Without it you could get a massive voltage surge in the stator. Most stators have an arc-gap so that if the voltage goes above a set limit, like 600 or 1000 volts, it will arc across. That's a last line of defense. On a generator, if excitation fails, you'd need to brake the prime mover to prevent the system from spinning out of control and flying apart. A turbine uses guide vanes to try and keep rotating at a set speed. You'd probably get a turbine trip. Physically, the exciters I've been around consist of a big grey cabinet, about 3' by 3' by 7', usually with a 59kVA isolation transformer in a smaller but much heavier grey cabinet. They'll probably have a DC voltage and DC current indicator on them, local/remote control switch, status lights (exciter on, breaker closed, field discharge resistor open/closed, applied field, fault, alarm) and an e-stop button. As far as failures go, I don't think an exciter failure would be very spectacular, unless something happened where the exciter failed and the FDR did not absorb the energy from the rotor. Even then everything would be inside closed cabinets. Maybe you'd get something a little like this: http://www.youtube.com/watch?v=nibB2c9djCo V - the shorter, more elegant answer. Three-Phase fucked around with this message at Nov 07, 2009 around 22:43 |
| # ? Nov 07, 2009 22:27 |
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Ibsen posted:For a layman, what is an exciter? All big generators use electromagnets instead of permanent magnets, electromagnets need to be "excited" or energized to produce a magnetic field.
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| # ? Nov 07, 2009 22:31 |
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And now, more videos of things going very, very wrong! http://www.youtube.com/watch?v=vCpH19TkMqo - 34kV switch failure ("HOLY F***ING RIGHT BABY!") http://www.youtube.com/watch?v=Au1nJ-2zg0w - 230kV vacrupter switch failure ("You OK?" "I'm OK!") http://www.youtube.com/watch?v=PXiOQCRiSp0 - 500KV vacrupter switch feailure ("F***!") http://www.youtube.com/watch?v=-Qq7U7tFsvQ - Arc flash, close up of initial 35000F fireball and slow-mo. Notice in the slow-mo how the feeder cables violently move apart from the massive magnetic fields the short circuit generates. Three-Phase fucked around with this message at Nov 07, 2009 around 22:55 |
| # ? Nov 07, 2009 22:50 |
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Cool. To clarify, the exciter is powered externally i.e. you need another power source to get a cold generator up and running, or am I missing this entirely. You probably need an Electrical Engineering degree for this line of work? It interests me because unlike other fields of physics it seems almost within reach because you can picture most of this in your head as to how these systems physically work.
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| # ? Nov 07, 2009 22:51 |
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Calast posted:What's the deal with 'power factor' and 'power factor correction'? Everyone who's had high school knows Watts = Amps x Volts. Except that if you go into an actual AC system and measure amps and volts, you'll find they don't equal the watts. The difference between Watts and what you get when you multiple Amps x Volts is called power factor. Ideally, Power factor is near 1.0; at 1.0, Watts=Amps x Volts. In practice, PF is generally between 0.8 and 1.0. Power factor correction (usually big banks of capacitors) is used to shift power factor closer to 1.0 because more power can flow through the same wires the closer power factor is to 1.0. Most homes are pretty close to 1.0 so it's nothing most consumers have to worry about.
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| # ? Nov 07, 2009 22:54 |
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^ - Grover is completely on the money here. Also, some people are trying to sell power factor correction units to homeowners. This is effectively a scam. However, in the future, I wouldn't be surprised if US consumers got billed for both reactive power used, as well as the time of day they used it.Ibsen posted:Cool. To clarify, the exciter is powered externally i.e. you need another power source to get a cold generator up and running, or am I missing this entirely. Small stuff can be excited with a permenant magnet, or self-excited with an additional winding where part of the output of the motor creates the excitation. This is possible because even when the electromagnet is de-energized, there is still a small amount of residual magnetism so the system can "bootstrap" itself. Incidentally, one challenge at a power plant is doing a "black start", starting back up all the generators and systems after the power grid crashes down. EE and EET are good lines of study for this stuff. One complaint I've heard is "all the EET kids focus on are microprocessors and computers". I think there's pretty good demand in the power field. My degree is batchelor's of science in electrical engineering technology (BS-EET). It's more applied and less theoretical than pure EE, but it still contained the basic math and physics required. Three-Phase fucked around with this message at Nov 07, 2009 around 23:03 |
| # ? Nov 07, 2009 22:58 |
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Three-Phase posted:What about small "peaking" units to provide temporary power while you crank up additional generation? Oh they're used. I can actually remotely control a few of them from work with our SCADA. (Including units with a sync cond for voltage control) Peakers are generally best used for emergency power - If a plant blows off line or a line trips (which is pretty common) you can call these things on quickly until you can dispatch another longer term resource. That keeps power from flowing in from other balancing authorities and keeps your frequency more stable. They're also called on during critical load times, but you'd hope that all the cheaper power has been dispatched first because they're generally not as efficient. Wind power is more unreliable than people think. There are some wind farms near by that have a reliability factor of around 30%. That is, over the course of the year you can expect the thing to be generating 30% of it's max. It could be pushing full power on some cold windy (and low load) nights, and it could be offline completely when you need it most, at the height of a hot day. (When was the last time you felt lots of wind when it was blistering hot?) Fossil fuels are in the high 90% range. Every time you add more wind to your mix, you need to back stop it with something more reliable *and* can fast ramp or your grid is going to go through hell and back trying to keep your frequency stable. Unless you're near a lot of water, those sources are fossil fuels. I attended a WECC scheduling course a while back as part of my training. It was pretty interesting learning about coordinated phase shifting, and altering the power angles on lines to crank more through, but I'm glad I don't have to deal with it on a daily basis.
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| # ? Nov 07, 2009 23:29 |
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Three-Phase posted:Well, for a fossil fuel plant, I'm assuming the resource cost is lessened - it's like a pilot light in your oven. The problem comes when you have to pay to staff three shifts of personnel while you aren't pumping out power. There's a certain break-even economic point where you're making money. If something takes down your generation, like a transformer catching fire in the switchyard, you're loosing money for every second you're down. That's pure loss - putting out 0MVA means taking in $0. Any unit that doesn't have full 24/7 staff (cogen facilities, coal units, etc) is going to be able to be remotely started and can be designed to run without 24/7 support. But then you're again talking about peaking facilities. You wouldn't build a coal unit that isn't designed to run 24/7 (maybe not at full capacity all the time, but it's going to be generating full time).
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| # ? Nov 07, 2009 23:35 |
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I hear everyone talking about rebuilding the U.S. electrical grid. Could you explain more in detail what is out of date, and what it would be replaced with? (I'm sure lots of substations could be upgraded, but what about long distance power/transmission lines?)
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| # ? Nov 07, 2009 23:59 |
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I have to say that this thread is awesome, but without an engineering background I'm finding myself pretty much flailing in it. So here's a layman question: How do you see the industry changing over the next few years? What do you predict the future to hold, and what has changed since you began working in the field?
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| # ? Nov 08, 2009 01:48 |
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Kaal posted:I have to say that this thread is awesome, but without an engineering background I'm finding myself pretty much flailing in it. So here's a layman question: How do you see the industry changing over the next few years? What do you predict the future to hold, and what has changed since you began working in the field? Oh sure. The big change over the next few years will be the smart grid - all the way down to consumers being able to go to a web site and track their power usage in real time - charting what they've used for the past month, week, day, or even hour. Also, the smart grid will allow for better monitoring and control, but there's going to be some bad growing pains when it comes to keeping the systems secured - not just from everday hackers but cyber-terrorists who could cripple the power grid! As far as the future goes, we're looking at several improvements. Such as better safety - the whole gambit from better training, better alarm management, arc-flash detectors that can see the flash and heat from an arc and open a breaker before equipment is damaged or a person is killed. Lots of things won't change. We have safety PLC equipment, and people still want "hard-wired" safety systems. There seems to be a lot of "if it isn't broke, don't fix it" in the power industry. I'm too new in the field to see change. I've only been doing this for about two and a half years. Even in that time, things like arc-flash safety have really moved to a forefront, this stuff (like being BURNED TO DEATH) apparently wasn't a big deal until the mid-90s.
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| # ? Nov 08, 2009 02:20 |
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Wow, I just read through the Wikipedia article on smart grids, and I have to say that deploying that technology looks like it's going to tricky business. Probably they'll start it off by offering it to industrial consumers first, and then having residentials try it on for size. Still, power leveling is a great way of decreasing our need for rapid infrastructure growth. Hopefully you guys will find a way of making it work. So what do you mean by "hard-wired" safety systems? Is that in comparison to software-only safety systems? Also, what kind of tools and such do you use, and what is your average work day like? What's involved in getting power from the coal plant to my computer? Haha. Can you tell that I'm a journalism major? Kaal fucked around with this message at Nov 08, 2009 around 03:50 |
| # ? Nov 08, 2009 03:47 |
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Kaal posted:So what do you mean by "hard-wired" safety systems? Is that in comparison to software-only safety systems? Also, what kind of tools and such do you use, and what is your average work day like? Hard-wired systems are where things like relay logic are used to turn on and off critical systems. A relay is essentially a little device that has a electrically triggered switch inside that can switch on and off other sources of voltage. You can string together relays in, well, "strings" so that if, say, you don't have oil pressure, you cannot start the motor or generator. You can do this via a PLC (programmable logic controller), but that's in software. For critical stuff, people still prefer physical relay logic. This gets cumbersome when you have 20 conditions that must be met to allow the device to run. As far as tools go, here are some useful items: 1. SKM Power Tools for power system analysis 2. Power analyzer for low-voltage systems 3. This book:  4. This book that better explains the previous book (would've had a picture but since three minutes have gone by, that means it's time for Waffleimages to poo poo the bed). My work days can be extremely varied. It includes design work, talking to vendors (people selling equipment), meetings, and going into the field to see how maintenance work is progressing. Protip: one of the worst things an engineer can do is ignore the technicians and operators out there in the field. Some engineers have fostered an environment of hostility by ignoring important information provided by the experienced people working on the floor. Kaal posted:What's involved in getting power from the coal plant to my computer? Can you tell that I'm a journalism major? Well, I can put it this way then: Over a hundred years of scientific research. Edison's DC work. Teslas' AC work. Engineers working late nights going over system protection schemes. The sweat-drenched protective equipment of the men and women working live equipment. The adherence to singular standards and ideas. The constant evolution of technology. The spouses and children of mommies and daddies that never came home from work that one day. That's what's involved in everything we do every minute of the day. Three-Phase fucked around with this message at Nov 08, 2009 around 05:20 |
| # ? Nov 08, 2009 05:02 |
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And now for a treat (unless you're deathly afraid of heights or electricity): http://www.youtube.com/watch?v=lcjhjna9jZE - Power washing insulators from a helicopter http://www.youtube.com/watch?v=9tzga6qAaBA - Aerial power line inspection - climbing onto the 500kV lines (I would literally poo poo myself if I was the one climbing onto the wire, not because of the electricity but because of the height!) Three-Phase fucked around with this message at Nov 08, 2009 around 05:27 |
| # ? Nov 08, 2009 05:25 |
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Sup substation buddy? Hope you don't mind me chiming in. Let's get this thread rolling.  This is what happens when you rack in a 27KV breaker with a loss of dielectric medium. BOOM. This breaker was being racked in, ie: a guy was standing infront of this breaker with a hand crank pushing this breaker into the cubicle to make up with the bus work and in this case a capacitor bank. He heard a buzzing sound then saw a blue flash; he jumped out the way just in time. The breaker got EJECTED out of the cubicle and smashed into the cubicle infront of it. 1. Why do those power poles carry wires in multiples of three? A) AC is run on 3 phases, one phase per wire. 2. What are (insert funny looking object in a substation) A) where to begin...All of those metal rods up in the air in a transmission station is called bus work or simply "bus". It is ALL energized with voltages such as 138KV or 345KV, all the way up to 500KV. There are porcelain insulators holding the bus up while keeping it from going to ground through the support beams. 3. Have you ever been shocked? A) Only have 16 months on the job, so no and I plan on keeping it that way. 4. How much power actually goes through power lines? A) I am not too familiar with the power factor, but depending where you are, distribution voltages can be 4KV, 13.5KV, 27KV, 33KV. 5. How does the grid work? A) You have multiple "feeders" ie: those 3 cables you see at the top of a utility pole all running under ground in a grid patten. You can lose one or more of these feeders and the rest will pick up the load because they are all connected. Grids are on the underground cable systems found in major cities. If you lose too many on a hot summer day for example, the rest of the feeders will overload because the demand is too high and will cause the cables burn up. A grid, or network, differs from a "loop system" in terms of reliability because a "loop system" is the overhead system; Those 3 wires you see at the top of a utility pole. That ONE feeder will be feeding an area, and if you lose that, you will lose service. 6. How do power outages occur? A) As I explained in the previous answer, Let's take a grid network during a hot summer day for an example. You have multiple feeders undergound all connected feeding an area. Air conditioners draw a lot of power. Now some of these feeders can be very VERY old. The insulation is beat up and cracked. Now the load put on the feeder generates heat. All of this will cause the feeder to fail. Now in a grid network the other feeders in that area will pick up the slack, however now they are getting overloaded/hotter now they start to fail. Lose too many feeders and the energy control center of your area may decide to dump your network to prevent further damage to the system. Now you have a power outage. 7. How do you turn on and off circuit breakers if the power goes out? A) DC power. Substations have batteries which are obviously DC. The control feeds for circuit breakers are DC for this exact reason. If you lose your AC, you have batteries so you can still operate breakers to open and close.
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| # ? Nov 08, 2009 05:46 |
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Some Guy From NY posted:Sup substation buddy? What PPE was he wearing? NFPA 70E gives a guideline that racking equipment over 1kV is an automatic level four if he had to have the door open, level two if the door was closed. Glad he was OK. No matter, that sort of PPE isn't made for ejecting equipment. I did hear about where we had something like a Multilin blown out of a cabinet during a fault. I'm hoping that more places get these robotic racking systems. They have these nice long control pendants so you can be standing like fifteen feet away while racking.
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| # ? Nov 08, 2009 06:24 |
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Three-Phase posted:What PPE was he wearing? NFPA 70E gives a guideline that racking equipment over 1kV is an automatic level four if he had to have the door open, level two if the door was closed. Glad he was OK. No matter, that sort of PPE isn't made for ejecting equipment. I did hear about where we had something like a Multilin blown out of a cabinet during a fault. Fire retardant clothing, Hardhat with faceshield, 35KV rubber gloves with leather gauntlets, and electrical insulated boots with safety toe. That is our standard PPE. edit: Yeah, there is a lot of talk about getting motorized racking mechanisims, but as of now we are still getting new breakers retrofitted which require hand cranking.
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| # ? Nov 08, 2009 06:28 |
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Some Guy From NY posted:Fire retardant clothing, Hardhat with faceshield, 35KV rubber gloves with leather gauntlets, and electrical insulated boots with safety toe. That is our standard PPE. With all due respect, I'm assuming fire retardant = Level 1. Be careful out there, and be careful with the face shields. I saw a particularly horrific video that demonstrated how non-arc flash rated face shields behave in these situations - the shield turns into molten plastic. If the victim is knocked over, they get a face full of burning plastic. Anyhow, I think that where I work is on the super-strict end of the spectrum as far as arc flash goes, especially with doing studies and getting specific labels on equipment (level of arc flash, calories per CM^2, voltage and equipment needed, approach boundaries, etc). Eventually it's gonna be a cost/risk versus benefit and everyone will want breakers both the can be remotely racked as well as switchgear with arc-flash detectors that can quickly open the upstream breaker to the bus. That will definitely save equipment and lives. Some Guy From NY posted:It is ALL energized with voltages such as 138KV or 345KV, all the way up to 500KV. There are porcelain insulators holding the bus up while keeping it from going to ground through the support beams. Up to 745kV for AC systems. For DC transmission lines like the one from the massive hydro plant in Sau Paulo, that's +/- 600kVDC for a total delta of 1.2MVDC. But those ultra-high voltages are not as common. Three-Phase fucked around with this message at Nov 08, 2009 around 06:38 |
| # ? Nov 08, 2009 06:34 |
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