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Did I really make the title "As me" instead of "Ask me"? Dammit, I'm so dumb as hell.  ABOUT ME I've been working for several years in the electrical power and controls field. It's been a blast (figuratively), I really enjoy my field. The job can be challenging and frustrating at times, but it's still rewarding to see something you designed come to life. INDUSTRIAL ELECTRICITY Large industrial establishments (chemical plants, steel mills, factories) use tremendous amounts of electricity. A power company typically supplies electricity to these users at a high voltage, from 6900V to 138000V. In a plant, that voltage is stepped down and transferred around the facility to where it's needed. There are three key components, transformers, breakers, and busses. Transformers - these step down (or up) a voltage. Typical ratios at a plant would be: 13.8kV to 4160V - this takes the electricity supplied by the power company and drops it to a lower (but still high) voltage for distribution around the plant 4160V to 480V (or 480/277V) - lots of equipment in a plant runs at 480V/277V, such as motors, heaters, and some high-bay lighting 4160V to 120/208V - this is for things like your computer, microwave oven, and some lighting Breakers - breakers allow parts of the power system to be "turned off" and isolated from one another. They also are designed to open in fault conditions, such as a short circuit, or an overload. Small breakers have a built-in trip circuit that says "hey, something's wrong, trip!" Large breakers need to be connected to a protective relay - something that looks at the electrical system and tells the big breaker "hey, something's f'ed up, trip!" Busses - these are like a power strip, you can plug different loads into them. A bus can be as simple as the metal strips in the back of a circuit breaker panel, or as complicated as metal-clad switchgear for moving thousands of amperes at thousands of volts. I've worked with machines that are much larger than most people deal with. Your garage door opener is 2 horsepower. In a large plant, there are motors bigger than 10,000 horsepower. SAFETY Humans and electricity don't mix. A voltage as low as 120V can, under the right conditions, kill. At higher voltages more current can flow through a person, and insulation can even be punctured. A pinhole in a rubber glove can be lethal at the right voltages. Special safety measures are taken at higher voltages, such as grounding equipment so that if it's turned on by accident, nobody is hurt. Even scarier is arc flash, where a short-circuit occurs in a piece of equipment, and suddenly there's a fireball that's hotter than the surface of the sun, and you're inside of it. Arc flash is more dependent on fault current than voltage. You can get a dangerous arc flash on large equipment operating at low voltage such as 120/208V or 277/480V. Particularly on the secondary (low voltage) side of a large step-down transformer. This video has a person involved in a relatively minor arc flash incident. He still may have suffered burns, eye damage, ear damage, etc. There are videos on YouTube of much, much more serious accidents where people didn't survive. - So if you want some funny stories, horror stories, or just are curious what's inside those big grey boxes with the warning signs on them, this is the thread for you! - Some additional videos: Closing 4160V breaker (PPE on improperly. Not good.) Stupid kid demonstrating fault-current availability Bringing a transformer online Bringing another transformer online - note that the red light means the circuit is energized (danger) and green light means the circuit is off (safe). Some places use the opposite color code. ELECTRIC ARC FURNACE - Turn your speakers DOWN. You need to phone the power company before you start one of these. I'm not joking. Three-Phase fucked around with this message at 17:01 on Sep 4, 2011 |
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Sep 3, 2011 14:15
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Do the big industrial customers still get 60Hz AC?
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Sep 3, 2011 20:46
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Naffer posted:Do the big industrial customers still get 60Hz AC? SHORT ANSWER In North America, yes. We operate at 60hz from 120V (your household outlets) all the way to the highest AC transmission voltages (800kV-ish). Many other places in the world operate at 50hz. LONG ANSWER The frequency you see at your outlets is based on the frequency that it's generated at, and that all depends on how the generator is built and how fast it spins. A four-pole AC generator, spinning at 1800RPM, will generate 60hz output. Likewise a 32-pole generator spinning at a much slower 225 RPM (like at a hydroelectric plant) will also generate AC at 60hz. So that you can have a power grid, where hundreds of generators are dumping energy into a huge bus, all the generators must provide electricity at the exact same frequency. When I've done power quality monitoring, the line frequency is usually between 59.99hz and 60.01hz. Typically the larger the bus, the more stable the frequency is. In other countries, especially islands, the frequency could me much more variable. The most important things about 60HZ AC (versus other frequencies) is that it impacts how transformers are sized/built, and the speed of AC motors. Three-Phase fucked around with this message at 21:34 on Sep 3, 2011 |
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Sep 3, 2011 21:25
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During your tests, how much does the voltage vary? I'm under the impression that over here in the UK everything works on 220+/- 10. Does that sound right / normal?
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Sep 3, 2011 22:08
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hermand posted:During your tests, how much does the voltage vary? I'm under the impression that over here in the UK everything works on 220+/- 10. Does that sound right / normal? 10% of nominal is generally regarded as OK (per the EN5160 power quality standard). I'm not familiar with UK power systems, but that does sound acceptable. Some of the worst swings I've seen when testing (we were experiencing issues with some small 480V motors) were from about 475V to 520V. That was a swing over a 24-hour period. I left the recorder on it (the motor terminals) for a week. Late at night the voltage would slowly creep up to around 520V, and during the day it would drop down to about 475V. This was the sort of power system in question: 32kV bus --(Transformer and breakers)-- 4160V bus --(Unit sub transformer and switchgear)-- 480V bus That sort of swing could be fixed by adjusting down the 4160V transformer secondary tap. (Electricity comes in at 32kV, comes out at 4160V , but you can change the output voltage plus or minus a percent or so.) Some facilities have automatic tap changers that detect the voltage being too high or too low, and mechanically switch to a different tap automatically. Because of the economic downturn, some major loads on the power company's grid started to go away. As they did, it looks like the system voltage creeped higher, and so that trickled-down through the entire power system. Three-Phase fucked around with this message at 02:07 on Dec 22, 2012 |
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Sep 3, 2011 23:15
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Have you performed many short-circuit and coordination studies? I'm an electrical engineer in the power industry, though I work more on the utility side of things. I've done quite a lot of protective relay coordination studies for both utilities and industrial clients (typically petrochemical). Some design work, as well. I'll let the OP answer questions as they pop up unless he/she wants me to chime in.
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Sep 3, 2011 23:16
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Three-Phase posted:That sort of swing could be fixed by adjusting down the 2400V transformer secondary tap. (Electricity comes in at 32kV, comes out at 2400V, but you can change the output voltage plus or minus a percent or so.) Did the transformer have an automatic load-tap changer on the secondary?
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Sep 3, 2011 23:17
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Anti-Hero posted:Have you performed many short-circuit and coordination studies? I'm an electrical engineer in the power industry, though I work more on the utility side of things. I've done quite a lot of protective relay coordination studies for both utilities and industrial clients (typically petrochemical). Some design work, as well. Not yet. All I know is you want to assume an infinite bus for short circuit studies, but you don't want to do that for arc flash studies. That and the equation for using the %Z for a transformer to calculate secondary short-circuit capability, stuff like that. As far as coordination, I've done some basic things looking at time-current curves using Power Tools, mainly to look at protecting small (100kVA) exciter/drive isolation transformers and similar equipment. I have the most basic knowledge of protective device coordination on low voltage systems. As far as protective relaying, I've only done work with the GE Multilins for large motor protection, I'd like to do more with equipment like the SEL relays. I'm assuming you (AH) are also doing things like distance protection relaying and more complicated reliability analysis - looking at what happens to the power system if any specific piece (or pieces) of equipment fail at any time. Feel absolutely free to add or discuss anything you'd like, AH! You're not stealing my thunder in the least. Anti-Hero posted:Did the transformer have an automatic load-tap changer on the secondary? No, on that bus we did not have one. I've seen some plants where they have busses that are specifically regulated medium-voltage busses (4160V) that use automatic tap changers. Sucks because we'd need an outage across several areas to change the taps. Have you ever seen a system where a tap changer introduces electrical transients into the system during operation? I'm talking transients that are significant enough to cause flicker, make UPS units go online, crash electronics, etc? Three-Phase fucked around with this message at 23:31 on Sep 3, 2011 |
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Sep 3, 2011 23:20
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Does anyone still get DC power transmitted to them or does everyone rectify AC nowadays?
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Sep 3, 2011 23:50
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bear shark posted:Does anyone still get DC power transmitted to them or does everyone rectify AC nowadays? HVDC is still used for transmission under special circumstances. While AC transmission is the most efficient for your average transmission line, once you get to REALLY long lines (say, 600 miles or more) HVDC becomes more economic. AC has the advantage of relatively cheap equipment used for transforming voltages to make them suitable for long-distance transmission, but the power losses for AC typically offset the equipment costs necessary for HVDC once you get to those long transmission lengths I mentioned earlier. HVDC is often used as an interconnect between two large systems because it's asynchronous. Some systems when they get large enough become very difficult to sync together. HVDC gets around that as it's all DC anyways, so there is no oscillating aspect to the current. I believe Texas can be considered it's own large islanded system with a couple of HVDC links to the rest of the power grid.
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Sep 4, 2011 00:35
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bear shark posted:Does anyone still get DC power transmitted to them or does everyone rectify AC nowadays? I really doubt it, especially since rectifying AC to DC is so much easier using power diodes and SRCs than, say, a mercury arc rectifier like the used to, or a motor-generator set. With the SCRs and some filtering, you can create DC at varying voltages as well. This is good for applications like electroplating, welding, etc. There are some limited HVDC applications, but those are mainly for transmission of huge amounts of power across very long lines. The efficiency savings in HVDC is offset by needing to build a thyristor hall for converting it back to AC, so you need to look at the costs carefully. Here's some cool HVDC videos: ABB HVDC Light - England/Wales Connection Siemens Ultra-High Voltage DC If you're ever driving and see a large power transmission line that only has two wires (instead of three or even multiples of three) it's likely a HVDC line! Three-Phase fucked around with this message at 00:44 on Sep 4, 2011 |
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Sep 4, 2011 00:37
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Can you talk more about how the heck you can turn circuits on and off under these sorts of currents and voltages? Isn't ionization of air related to voltage so with high voltages, air is no longer enough of an insulator (eg: if you just try to mechanically withdraw a metal contact it will form a spark and ionize the air)? I also wonder how the contacts aren't fried even if you don't have arc issues keeping the thing energized... a contact that large made of gold or silver would be freakin' expensive, but anything else is going to quickly corrode. Also re:Texas, yes most of Texas is on its own independent power grid. We have several DC-DC connects with the eastern grid and one with the western grid IIRC. These are DC-DC but all housed in the same building so the transmission losses aren't an issue - it is the frequency synchronization issue mentioned above. You can check out the current wars article on wikipedia but DC is more efficient, it is just harder to make simple motors and until solid state electronics, there was no easy/cheap/small way to step DC voltages up and down (but transformers for AC power are trivially easy to make). So we deployed AC because we needed higher voltages to move power long distances, but we had no way to step DC up and down, thus AC won the current wars. You should check out the mercury arc rectifiers... some of them were huge 6-8 ft glass bulbs where A/C was injected at the electrodes at the bottom and as the AC phases made their cycle, the arc would pass between different electrodes, resulting in a somewhat stable DC output. The mercury vapor would hit the glass, cool, condense, then trickle back down to the pool at the bottom. I find it ironic that the vast majority of devices people use these days (at least in the home or office, not the plant floor) run on DC power... everything except stuff like heating elements and large motors. We waste so much electricity piping AC long distances then converting it into DC... its almost like we would have never deployed AC power if we could have made cheap DC voltage changers back in the day. It's also why places like data centers are starting to install a few central rectifiers then deploying DC power hookups to the servers/equipment... then all the PSU does is simple voltage conversion, which helps control heat and makes the PSU more reliable. I'm not sure if they approved standard outlets and whatnot for DC power yet. Three-Phase posted:I really doubt it, especially since rectifying AC to DC is so much easier using power diodes and SRCs than, say, a mercury arc rectifier like the used to, or a motor-generator set. With the SCRs and some filtering, you can create DC at varying voltages as well. This is good for applications like electroplating, welding, etc. IIRC there were still a few DC customers in the NY area (from the original edison days) but they were switched over in the 1990s/early 2000s by installing rectifiers on-site. Also the last mercury arc valves were replaced with solid state devices (or at least that was the plan last I heard... I'm no expert). I believe the costs for these devices are continuing to fall and it is likely that in the future HVDC will be much cheaper to implement. Of course they are also testing superconducting transmission lines using liquid nitrogen cooled wires. In theory a very small wire could carry massive loads... as long as it never warmed up... then I expect "vaporized" wouldn't do justice to what happens to it. Simulated fucked around with this message at 00:54 on Sep 4, 2011 |
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Sep 4, 2011 00:47
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^ - I read about those superconducting wires too! Neat stuff, if we can get better superconductors (ie: room temperature) it will be an absolute godsend to the power industry. Ender.uNF posted:Can you talk more about how the heck you can turn circuits on and off under these sorts of currents and voltages? Isn't ionization of air related to voltage so with high voltages, air is no longer enough of an insulator (eg: if you just try to mechanically withdraw a metal contact it will form a spark and ionize the air)? That's right. Even flipping a lightswitch will generate a small arc. In a big circuit breaker, the effect is much more intense and can be catastrophic. There are a few tricks: 0. Opening the contacts fast enough that an arc cannot easily sustain itself 1. (Smaller/medium breakers) Have arc chutes - when the breaker opens, the arc flows up into these dividers, gets split up and cools, until the arc cannot sustain itself 2. Use the magnetic field generated by the flowing current slam into the magnetic field generated by the arc and blow it into an arc chute 3. Use compressed air to blow the arc out 4. Flood the contracts in oil 5. Flood the contacts in Sulfur Hexaflouride, an insulator 6. Keep the contacts in a vacuum bottle 4, 5, and 6 are generally used more in high-voltage circuit breakers (over 600V). Also, breakers have an AIC - ampere interruption capability. So you buy a 120V, 20A breaker, it may have a 10,000 AIC. What that means is that for a fault under 10,000A, the breaker should be able to interrupt the arc. If it's over 10,000A, it may not be able to stop the arc (and will probably blow up in the process.) You need to look at the makeup of the power system and say "gee, this breaker is only rated at 10,000A. If I short out what this is connected to, will more or less than 10,000A flow through it? Will something else break the circuit in time?" Another fun thing about big breakers is they need electricity to operate, typically 125 volts DC. You energize the close coil to close the breaker, you energize the trip coil to trip the breaker. Or you have power constantly applied to close and hold the breaker closed, and when you remove power the breaker trips. Tidbit - disconnect switches Companies also make disconnect switches, these are generally used for safety, so you can "unplug" a large device. Sometimes the circuit breaker powering a device may be in another area of a building, and you don't want someone turning a medium-voltage motor on when you're working on it. These disconnect switches are either load interrupting or non-load interrupting. Load interrupting is like a household light switch. It interrupts the load. A non-load interrupting switch must NEVER EVER EVER be closed or opened with the potential for current to flow through it, or with current flowing through it! It the mechanism doesn't operate fast enough, it can cause a violent explosion within the disconnect switch. This is what happens when you open a large disconnect under load! Three-Phase fucked around with this message at 01:09 on Sep 4, 2011 |
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Sep 4, 2011 00:54
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Three-Phase posted:1. (Smaller/medium breakers) Have arc chutes - when the breaker opens, the arc flows up into these dividers, gets split up and cools, until the arc cannot sustain itself Doesn't the arc in these sort of situations degrade the contacts? I presume there would be a limited number of disconnects before it is no good... actually I think the cheap non-silvered home light switches have the same issue. I know I've had to replace one or two that would audibly arc when switched on/off and I presume that was due to oxides and crap building up on the contacts. quote:Also, breakers have an AIC - ampere interruption capability. So you buy a 120V, 20A breaker, it may have a 10,000 AIC. What that means is that for a fault under 10,000A, the breaker should be able to interrupt the arc. If it's over 10,000A, it may not be able to stop the arc (and will probably blow up in the process.) You need to look at the makeup of the power system and say "gee, this breaker is only rated at 10,000A. If I short out what this is connected to, will more or less than 10,000A flow through it? Will something else break the circuit in time?" Awesome. I also like the video of the oil-cooled transformer exploding as it superheats the oil. Not sure what would cause that though, given the oil they use is non-conducting. I would presume most people who try to flip a non-load interrupting switch aren't around to talk about it. Do they usually have safety sensors to prevent you from operating it while under load? For that matter, it makes me wonder how industrial equipment can be switched on and off... or even if it can be switched off internally. I have no idea how you'd make a regulator that could control the motor speed of a 10,000 HP motor.
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Sep 4, 2011 01:09
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Ender.uNF posted:I find it ironic that the vast majority of devices people use these days (at least in the home or office, not the plant floor) run on DC power... everything except stuff like heating elements and large motors. We waste so much electricity piping AC long distances then converting it into DC... its almost like we would have never deployed AC power if we could have made cheap DC voltage changers back in the day. It's also why places like data centers are starting to install a few central rectifiers then deploying DC power hookups to the servers/equipment... then all the PSU does is simple voltage conversion, which helps control heat and makes the PSU more reliable. I'm not sure if they approved standard outlets and whatnot for DC power yet. Similar issues complicate its use for distribution. 12V transmission requires 10x as large of a wire for the same power as you would need for 120V transmission, and that copper all costs a lot of money. A typical computer uses a mix of 12V, 5V, 3.3V (and other voltages), so even if you invested in the copper and have 12V distribution, you're still going to need a power supply to convert that to the lower voltages. Ends up being pretty much no advantages over standard AC distribution when everything is accounted for. DC is very prevalent in the phone industry, though; they use a lot of 48VDC.
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Sep 4, 2011 01:23
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Ender.uNF posted:Doesn't the arc in these sort of situations degrade the contacts? I presume there would be a limited number of disconnects before it is no good... actually I think the cheap non-silvered home light switches have the same issue. I know I've had to replace one or two that would audibly arc when switched on/off and I presume that was due to oxides and crap building up on the contacts. Residential breakers like you have in your house just have one set of contacts, and are frequently damaged from the arc when they break under load- the increased contact resistance from repeated trips increases temperature and causes them to nuisance trip at lower current levels. Which is part of why they're not supposed to be used as switches. Fortunately, they're cheap and easy to replace. grover fucked around with this message at 01:31 on Sep 4, 2011 |
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Sep 4, 2011 01:26
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Ender.uNF posted:Doesn't the arc in these sort of situations degrade the contacts? I presume there would be a limited number of disconnects before it is no good... actually I think the cheap non-silvered home light switches have the same issue. I know I've had to replace one or two that would audibly arc when switched on/off and I presume that was due to oxides and crap building up on the contacts. I believe that in breakers, there are sometimes "flicker blades" that are where the arc starts/goes during operation. Those don't conduct electricity when the breaker is closed. The idea is that when the breaker operates, the arc is specifically directed to those blades. For a light switch, you're only talking about interrupting a few amperes as well, so the problems are likely not as severe. The problem is when you're a circuit breaker (let's say 480V, 100A) trying to interrupt a 15,000A short circuit. quote:Awesome. I also like the video of the oil-cooled transformer exploding as it superheats the oil. Not sure what would cause that though, given the oil they use is non-conducting. Non-conducting != really, really flammable quote:I would presume most people who try to flip a non-load interrupting switch aren't around to talk about it. Do they usually have safety sensors to prevent you from operating it while under load? Even better. There's a thing called interlock keying. What you have is a special lock and key on the circuit breaker compartment, as well as the disconnect switch. These are special keys and locks that can mechanically hold a key in place. It's set up so that you need a key to mechanically operate the disconnect switch. To get the key, you need to have the circuit breaker open. Once it's open, you can remove the key, take it to the disconnect switch, and operate it. That also prevents someone from closing the breaker while someone's messing with the disconnect switch. The trade name for this is commonly called "Kirk Keying", at least around Ohio. My understanding is it was developed in the early part of the 20th century as a lot of people kept being accidentally killed by this sort of problem. Here's another video on trapped key interlocks Also, there's operator competence - people working on these systems are trained to understand how they work, what the risks are, and how to safely do their jobs. quote:For that matter, it makes me wonder how industrial equipment can be switched on and off... or even if it can be switched off internally. I have no idea how you'd make a regulator that could control the motor speed of a 10,000 HP motor. For a large synchronous motor, 10,000 HP, you don't really need a regulator. If it's properly loaded, a four-pole synchrnous machine will rotate at very close to 1800 RPM on a 60hz line. Now if you overload the motor mechanically and it pulls out, that's another story. On my systems if there's a pull-out, the exciter for the motor (it generates the DC electromagnet inside the rotor, the rotating bit) will detect it, fault the exciter, and trip the motor out. The protection relay can also alarm to warn the operators if the motor is overloading. (That relay will also tell the SCADA (supervisory control and data aquisition system) what's going on. So the operator will see screen like this: code:As far as turing on and off, companies do make vacuum contactors to turn on and off very high voltages and current, but are not designed to interrupt faults like a breaker can. The easiest way to do this is to have a soft start/soft stop drive that can gently decrease the voltage/current until it's zero, and then the breaker or contact opens. Three-Phase fucked around with this message at 02:01 on Sep 4, 2011 |
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Sep 4, 2011 01:29
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Three-Phase posted:
The station I work at has been switching over to vacuum breakers on all of the 13.8 switchgear. The older arc chute style breakers moved the main contacts about 6 inches to break the contact. The new vacuum breakers move the contacts just over an inch and require no pre arcing contact. I maintain the generator excitation system at work so I can answer some questions about that aspect of power generation.
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Sep 4, 2011 02:54
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helno posted:The station I work at has been switching over to vacuum breakers on all of the 13.8 switchgear. The older arc chute style breakers moved the main contacts about 6 inches to break the contact. The new vacuum breakers move the contacts just over an inch and require no pre arcing contact. One of the things I really like on ABB's new AMVAC medium-voltage vacuum breakers is that there's under 10 moving parts. That's basically no-maintainance compared to other, older arc chute breakers that have tons of moving parts. I've seen only vacuum on 13.8 equipment, highest I've seen air-blast or magnetic-blast on is 7200V. I was looking at a model of one and literally said "That's it?" Plus there's no need for anti-pumping circuitry or any of that other bullshit, just a command to close, a command to open, control power, and status outputs from the breaker aux contacts. Plus you can also program the breaker to automatically trip on loss of control power, or after so many seconds without control power, if you so desire. One interesting thing about the vacuum bottles (the container holding the contacts) - I read that you need to be careful if you perform hi-pot testing on them. If there's a small gap between the contacts and you apply HV, you can start to generate X-rays. helno posted:I maintain the generator excitation system at work so I can answer some questions about that aspect of power generation. What's your opinion on brushless exciters? Where I work I've only heard bad things about them, they want slip-rings all the way. Also, when you have multiple generators on a bus, do you need to match the power factor (via excitation) on each of the generators? I think you'd have to. Do you have any synchronous condensers, or know any company that uses synchronous condensers? Three-Phase fucked around with this message at 03:13 on Sep 4, 2011 |
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Sep 4, 2011 03:00
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The DC breakers we use on the exciters are incredibly simple compared to the old arc chute breakers we use. Only a handful of moving parts. A big coil to move it and a few tiny trip coils and a metal plate that presses a row of micro switches for aux contacts. All we really check is that the aux contacts all move at close to the same time and that the pre arcing contact opens after and closes before the main contact. It's a good thing it is simple because the german to english translation of the manual was really really bad. Regrding exciters. I have never worked with brushless exciters but the PSS people seem to hate them because it is hard to verify the computer modeling of them because you cant directly measure the rotor potential. I am quite happy to change generator brushes on a weekly routine but it is a bit freaky knowing each brush holder carries about 120A (2700A/22holders). We run four 900 Mw units and they dont share main output or station service transformers so we are able to run different reactive power on each unit. They get tied together on the 500 kv lines at the switchyard. helno fucked around with this message at 03:20 on Sep 4, 2011 |
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Sep 4, 2011 03:13
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helno posted:It's a good thing it is simple because the german to english translation of the manual was really really bad. Siemens or ABB?  One of my professors in college did something neat once - we were given the datasheet to a component, I think it was a memory chip, but it was in german. We had to pick through it and figure it out. That was a clever man, and it was a very good lesson. Just keep an eye out for "LEBENSGEFAHR!" and "HOCHSPANNUNG!" ABB really just needs a high-end option on their larger drives to deliver a polite german man named Jörg with the drive. (For maintaining the drive as well as conversation.) Three-Phase fucked around with this message at 03:26 on Sep 4, 2011 |
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Sep 4, 2011 03:18
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Its a GE DC breaker. Most of our other stuff is westinghouse. Tons and tons of really obsolete but reliable protective relays.
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Sep 4, 2011 03:22
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helno posted:Tons and tons of really obsolete but reliable protective relays. Oh yeah, built like a rock. I still like the newer relays with the little electronic screens (which sometimes don't flip out and display junk characters like on the Multilins). helno posted:Regrding exciters. I have never worked with brushless exciters but the PSS people seem to hate them because it is hard to verify the computer modeling of them because you cant directly measure the rotor potential. I am quite happy to change generator brushes on a weekly routine but it is a bit freaky knowing each brush holder carries about 120A (2700A/22holders). Wow, 900MW is nothing to sneeze at. Are those air, water, or H2 cooled? Do you have high-pressure "lift oil" systems on those generators to push up the rotor to make them easier to start by the prime mover? Also, are those generators connected via phase-isolated bus ducts? Three-Phase fucked around with this message at 03:33 on Sep 4, 2011 |
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Sep 4, 2011 03:27
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Three-Phase posted:I'm assuming you (AH) are also doing things like distance protection relaying and more complicated reliability analysis - looking at what happens to the power system if any specific piece (or pieces) of equipment fail at any time. I do quite a bit of distance protection, specifically communication-based tripping schemes. I also do a good deal of work involving substation control schemes integrating the protective relays with SCADA. I have not seen a system up here where a tap changer did that, but I don't really deal with stuff like that. I'm strictly a design & protection engineer, when I do field work it's typically to test the relays, commission them, or troubleshoot them. Oh, and Multilins are junk. Have you guys had any experience with SEL's motor relay? We spec SEL's exclusively so I'm very familiar with their relays used most often for utilities, but have never messed with their industrial stuff. I hope they are a decent alternative to the Multilin's that most people use. I really hope someone comes out with something that will compete with GE's protection offerings in the industrial industry, I've not been impressed at all with their relay's reliability. fake edit: Have you guys seen GE's new 480V arc-dome product? It's a standalone cabinet that is integrated with existing switchgear to reduce arc flash incident energy levels. It has a dome that is made up of 3 electrodes separated by air. During a fault, photo-sensors detect the light from the event and trigger the electrodes which ionize the air and create a lower resistance arc than the fault, "stealing" all the energy and exhausting it in the dome. Pretty neat stuff, we had some GE sales reps come by the office a couple weeks ago and show us some promotional materials. Anti-Hero fucked around with this message at 04:10 on Sep 4, 2011 |
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Sep 4, 2011 04:04
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How did you get started in the field? I'm currently a student in an Electrical program at a tech college. Anyway they thought us some residential commercial stuff, but I've had the most fun doing industrial and control work. Basically I'm having a hard time finding a place willing to hire me with no experience beyond school. Any tips?
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Sep 4, 2011 04:10
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tworavens posted:How did you get started in the field? I'm currently a student in an Electrical program at a tech college. Anyway they thought us some residential commercial stuff, but I've had the most fun doing industrial and control work. Basically I'm having a hard time finding a place willing to hire me with no experience beyond school. Any tips? That's just how the market is right now. Are you working on your Associate's or a Bachelor's degree? My work progression has been pretty simple. I went to an ABET accredited school for my BSEE and interned one summer for a power engineering consulting firm. They offered me a full time position after I graduated and I've been in the industry ever since.
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Sep 4, 2011 04:19
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Anti-Hero posted:fake edit: Have you guys seen GE's new 480V arc-dome product? It's a standalone cabinet that is integrated with existing switchgear to reduce arc flash incident energy levels. It has a dome that is made up of 3 electrodes separated by air. During a fault, photo-sensors detect the light from the event and trigger the electrodes which ionize the air and create a lower resistance arc than the fault, "stealing" all the energy and exhausting it in the dome. Pretty neat stuff, we had some GE sales reps come by the office a couple weeks ago and show us some promotional materials. It's a neat idea, better safety and protection of surrounding gear. Does the dome need to be replaced or inspected after intercepting a serious fault? I've seen similar products that use a light/current detection scheme, but just shunt-trip a breaker rather than use the dome. However, the trend I'm seeing is more of a "no live work, period" attitude where I'm at. That and more and more people are using simple remote-racking for large circuit breakers, since that's one of the most dangerous operations. Bummer about the Multilins, but you're not the first person to tell me they're junk. Oh well, we always make sure to put the NO "service" contact in series with the NC trip contact. If the relay goes south, it should trip the breaker. One of the most nerve wracking moments was once during testing when we had a motor trip unexpectedly. I check the Multilin and it's indicating a trip condition and over 300 degrees Celcius on one (just one) of the motor RTDs, I nearly poo poo myself! It turned out to be a bad connection to the RTD, thank god. The discussion between me and my boss was basically "if it was that high, we'd smell it, and the windings would practically be on fire". The one cool thing about the Multilins is the emergency restart contacts if you short them together, it makes the Multilin "forget" the stored thermal data, so you can immediately restart a stopped motor without waiting X minutes for a cooldown due to the starts per hour setting. Of course, this is only for emergencies (like if you need to restart a ventilation fan supplying air to a mine shaft) and testing without a load. It's kinda like in Star Trek where the captain just says "override" when the computer wants to stop him from doing something. You CAN seriously damage or reduce the life of a million-dollar motor with those contacts, so you need to be very, very careful. I've only ever shorted them with very explicit permission from a higher-up (literally unlock and open the cabinet, take a strand of wire, and short the contacts together until it indicates a restart on the screen). Anyone on the shop floor should NOT have access to this. Or access to anything on the Multilin for that matter, or the cabinet containing the Multilin, etc. Some of the people I've talked to act like the fact that you can do this is a trade secret, and I don't blame them. Three-Phase fucked around with this message at 04:55 on Sep 4, 2011 |
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Sep 4, 2011 04:37
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Anti-Hero posted:That's just how the market is right now. Associates degree. But since starting the program I've accrued a lot of credits toward a Bachelors degree if I want if and I think I want to go back to school in a few years.
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Sep 4, 2011 06:59
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Anti-Hero posted:fake edit: Have you guys seen GE's new 480V arc-dome product? It's a standalone cabinet that is integrated with existing switchgear to reduce arc flash incident energy levels. It has a dome that is made up of 3 electrodes separated by air. During a fault, photo-sensors detect the light from the event and trigger the electrodes which ionize the air and create a lower resistance arc than the fault, "stealing" all the energy and exhausting it in the dome. Pretty neat stuff, we had some GE sales reps come by the office a couple weeks ago and show us some promotional materials. Speaking of which, have either of you (or anyone else) seen or used and solid state breakers yet? I've heard they exist, and see big advantages in reducing arc flash, but I'm still a bit wary. grover fucked around with this message at 11:51 on Sep 4, 2011 |
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Sep 4, 2011 11:47
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grover posted:Speaking of which, have either of you (or anyone else) seen or used and solid state breakers yet? I've heard they exist, and see big advantages in reducing arc flash, but I'm still a bit wary. Drives have current limiting and fault detection, so sometimes they can act to interrupt a fault before a circuit breaker will. The only issue is that if the fault is severe enough, a current-limiting or silicon protection fuse on the drive will probably blow as well (within a half-cycle). (The fuses in a big air-cooled MegaDrive LCI are about $1000 each - not cheap to replace.) I would only trust a solid-state breaker if it was coupled with high interrupting capacity fuses as well as a fail-safe should the electronic section fail in any way. Maybe we'll see SSB's as more of a contactor replacement in the near future, where you have applications where the open/close cycle is high enough to reduce the life of normal breakers and contactors? (Do not confuse the ABB Megadrive with the Sega Megadrive. This is important.) Three-Phase fucked around with this message at 12:47 on Sep 4, 2011 |
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Sep 4, 2011 12:42
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Hope Three-Phase doesn't mind me jumping in...I am a substation operator and I have what everyone loves to see...PICTURES! Here is a 345KV circuit breaker built in the 1960s, and later modified. The Contacts are in the football looking section at the top. The 2 columns on either side which lead to those round tanks contain Current Transformers which monitor, you guessed it, current. It is a SF6 filled breaker, something Three-Phase touched upon earlier. The SF6 gas is the insulating medium.  Compare that breaker to a modern 345KV breaker:  This is the Hitachi HVB. Much more compact and less complicated. Here is a Transformer which is dropping 345KV to TWO 138KV feeders.  Here is a 27KV circuit breaker that failed:  That breaker uses a vacuum to interrupt the arc. What happened was, this breaker was used for Capacitor Bank switching and apparently could not handle the incredible inrush of current. One of the contacts literally welded itself together. The indication showed OPEN and as it was being racked into connect, there was an arc because of the welded closed contact. BOOM. No one was hurt. Remember:  Bonus: 
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Sep 4, 2011 19:49
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Some Guy From NY posted:Hope Three-Phase doesn't mind me jumping in...I am a substation operator and I have what everyone loves to see...PICTURES! What parts of these would be safe to bump into? I've always viewed substations as death mazes where bumping into absolutely anything will kill you instantly.
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Sep 4, 2011 22:25
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Crackpipe posted:What parts of these would be safe to bump into? I've always viewed substations as death mazes where bumping into absolutely anything will kill you instantly. Indeed, it looks like a death trap to walk around in there while energized. I presume there are designated foot paths that have a somewhat lower chance of electrocution.
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Sep 4, 2011 23:19
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Crackpipe posted:What parts of these would be safe to bump into? I've always viewed substations as death mazes where bumping into absolutely anything will kill you instantly. You want to be very careful, it's not even as simple as what not to bump into. If you're close to an energized conductor at, say, 500kV, you don't need to touch it. If you get close enough, and you're grounded (even wearing rubber sneakers) the electricity can jump from the line and slam into you. There are minimum working distances that specify "a worker (even with PPE - personal protective equipment) shall NOT be closer than A feet on a B voltage system." Even if you're very well insulated, you may create a capacitive path to ground, and can still get fried. Some of these systems can be incredibly dangerous. I've seen photos of someone who trespassed into a substation and made contact with an energized line. You might not want to read this next part. The "charred corpse" portrayal of someone who died under similar circumstances in the game Half Life 2 were pretty similar. When loading the body onto a gurney, one of the man's legs just broke off and had to be set aside. His skin was charred pitch black, almost down to the skeleton. He was effectively carbonized by the electricity. Also, if a wire that's very high voltage falls onto the ground, it's possible that a voltage gradient can be created across the ground. So let's say you take a big step with 3 feet between each of your shoes. That could be ten thousand volts or more, and you can get electrocuted. In the rare event you are ever standing near where a power line falls to the ground, you're supposed to hop with both feet (like you're in a potato sack race) away, or shuffle with very, very small steps until you're at least like 30 feet from the exposed line. (In a substation, a properly designed grounding grid may limit the size of the gradient and improve safety.) With all that said, the conductors are usually supported by insulators, which look like stacks of dinner plates. The higher voltage equipment also have those metal "halos" on them - that's to reduce the effect of corona discharge. You put a really high voltage on a sharp point, like the head of a pin or the edge of a metal connector, you can develop corona. Ender.uNF posted:Indeed, it looks like a death trap to walk around in there while energized. I presume there are designated foot paths that have a somewhat lower chance of electrocution. Typically equipment is installed high enough to prevent someone from walking under it from being electrocuted. However, that's not a bulletproof assumption. There are still tons of dangers. If you're elevated somehow, or moving something like a pole or a long tool, it can quickly get much more deadly. There was an unfortuante death of someone putting up siding on a house awhile back near Columbus, where his little ladder swayed in a gust of wind over into an overhead powerline, and it killed him. There are a lot of similar deaths that occur each year where a piece of equpment, a radio antenna, or a tool makes contact with a line. That line was probably only 7200V, where this stuff can be as high as 500000kV. . As far as safety goes, to work inside a substation, you need to: A. Understand the system, how it works, and the dangers involved B. Have a clear plan of what you're going to be doing (troubleshooting a breaker that isn't closing, checking for hotspots with a thermal imager, repairing or replacing an insulator or pothead, etc.) C. Have the protective gear, rubber insulating mats, hot sticks (insulating poles for holding tools), high-voltage detectors (you hold them near a line, and they beep and light up if there's AC on it, up to hundreds of thousands of volts), and all the other tools you need. Your gear also has to be routinely tested, like making sure there are no pinholes on gloves or rubber sheets. D. Have radio communication to the control room for the substation E. Have a buddy with you at all times, preferably away from you, who knows how to respond in an emergency, how to safely free you if you make contact with HV, etc. Those factors combined can make work much more safe, probably safer than, say, crossing a busy street. Some Guy From NY posted:Here is a Transformer which is dropping 345KV to TWO 138KV feeders. SEXY. How many MVA is that? 500? 1000? Three-Phase fucked around with this message at 23:58 on Sep 4, 2011 |
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Sep 4, 2011 23:37
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A lot of the linked videos and posts in this thread talk about "VA"s which I assume is volts * amperes. Don't we call those watts (W)? Or am I confused? Maybe it's just tradition to talk about volt-amps instead?
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Sep 5, 2011 00:35
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Tellara posted:A lot of the linked videos and posts in this thread talk about "VA"s which I assume is volts * amperes. Don't we call those watts (W)? Or am I confused? They're different. Volt-Amps are the product of RMS voltage and RMS current and measure the apparent power.
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Sep 5, 2011 00:46
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The Proc posted:They're different. Volt-Amps are the product of RMS voltage and RMS current and measure the apparent power. Cool, I guess I should have majored in EE instead of computer science...
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Sep 5, 2011 00:51
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See, there's three parts of the "power triangle": -Apparent power -Real power -Reactive power This all has to do with AC circuits. -Apparent power is just what it says on the label, the apparent power consumed by a system. -Real power is actual power that does real work, like heating a resistor, turning a motor, lighting a bulb, etc. -Reactive power is power that gets "bounced back" to the source. This doesn't do any real work, but consumes current anyways. A capacitor or inductor is a purely reactive load. The relationship is like a right triangle: Apparent Power ^2 = Real Power ^2 + Reactive Power ^2 Reactive power is classified as "leading" or "lagging" by a certain amount, or the power factor of a system. PF at 1.0 is neither leading or lagging, or unity. It then goes to 0 either in the leading or lagging direction. So let's say you have two motors, both are 10 horsepower. One operates at a 0.95 power factor, and another operates at a 0.8 power factor. The one with the 0.8 power factor is going to consume more current to do the same amount of mechanical work as the one with the better 0.95 power factor. - A small customer is billed based on volt-amperes (correct me if I'm wrong on this and it's just watts - I'd assume they'd measure VAs to account for reactive power). If you're a large to huge customer, like a steel mill, you are billed (and can even be fined) based on your power factor - how much reactive power versus real power you consume. Some factories have things like big motors that have a lagging power factor, so they install either power factor correction capacitors (which lead and cancel out the lag), or they install synchronous condensors - basically unloaded synchronous motors that just convert real power to leading reactive power. (All you do is decouple the motor, get it spinning, and overexcite the rotor!) Power factor correction is pretty important. Say you have a big mill and you start a dozen 10,000 HP motors in the morning without your PF correction capacitors in. The power company might see this and say: "Hey, you pulled 100 million volt-amps and 40 million VARs (volt-amps reactive) this morning for five minutes. We're now going to fine you $x0,000 for doing that in addition to the extra power costs. It's in the agreement your company signed. Sucks to be you." Yeah, some facilities (steel mills, etc.) are so massive that they need to talk to the power company on a daily basis to go over what loads they're running. I've seen situations where we were told by the power company to please not run large loads during ultra-hot days in the summer due to concerns about the stability of the power system, where an extra 200MVA load would not be well received. In some facilities where the motors can be decoupled, the tables can turn on the power companies on hot days. The poco may call up and say "Hey, could you please decouple several of those 10,000 HP motors and supply us VARs? We'll pay for it! Please! The million air conditioners running today is killing us, we're down to 130kV on our 138kV lines and we don't want rolling blackouts!" (That sort of thing needs to be arranged ahead of time, of course, but I've heard of some industrial customers doing just that - offering to create extra VARs for the power company by decoupling and overexciting their big synchronous motors.) Three-Phase fucked around with this message at 01:53 on Sep 5, 2011 |
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Sep 5, 2011 01:38
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The agreement with the Ontario power authority requires all generators to be able to take up to 30% of real power as reactive power. This is why wind farms always have those huge capacitor banks. They use inductive generators and cannot use excitation to take or push vars. You can see pretty clearly the reactive power loading every morning as things start to get turned on across the province.
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Sep 5, 2011 02:01
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Regarding power factor, I've noticed recently that there is a lot of bitching going on about PF in regards to Compact Fluorescent light bulbs. Does this amount to anything or is it just people choosing to bitch about anything they can find to bitch about? I'd think that something that draws as little power as a CFL wouldn't really be enough to make someone care one way or the other. lots of results in google: http://www.google.com/search?q=cfl+power+factor&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
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Sep 5, 2011 02:18
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