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squeakygeek posted:This is a really interesting idea--haven't heard of it before. I work in a research MRI lab and was just thinking about how much energy might be stored. Do you have any interesting references off hand? http://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage
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Oct 17, 2013 00:31
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This is more commercial electricity, but deals with arc flash. A couple of years ago, a bar I frequented burned down. No official cause was ever determined, beyond "it started in the kitchen while the place was closed". I shot some pictures of the place afterwards, and shot this blurry photo behind it.  To my untrained eye, I'm guessing this was a result of one of the breaker panels burning up inside the building during the fire, and this breaker decided to go  when it tried to open? If it helps, it was a late 70s/early 80s building. The owner of the hair salon next door was convinced this is what started the fire.. despite no fire damage near that breaker.  The building was condemned by the city after the owner's insurance said 3 of the 4 walls were salvageable and refused to pay out for a teardown, it's been 2 1/2 years since the fire and 1 year since it was torn down, still a bare slab with a neon sign in front with a promised reopening by superbowl. randomidiot fucked around with this message at 11:12 on Oct 19, 2013 |
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Oct 19, 2013 11:00
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some texas redneck posted:This is more commercial electricity, but deals with arc flash. Maybe we should change the thread title, because I think this sort of thing absolutely applies to this thread. I'm not a certified electrician or fire investigator, but that seems to be a possible clue. Are these panels outdoors? Why are there no covers on the panel? Could someone come by and just operate the breaker without opening the panel? It sort of looks like these panels aren't designed to be used outdoors despite the little "rain cover" that was installed, unless these were modified or salvaged after the incident for whatever reason. As far as breakers go, they aren't a bulletproof vest by any means. There are conditions where a breaker will not operate, such as high-impedance series arc faults (hence the movement towards AFCI breakers for homes, specifically places like bedrooms), or if the breaker is physically in poor condition. (Or for much larger breakers, if you lose control power, unless the breaker has a backup power source that allows it to trip on the loss of control power.) I don't think it's the case here, but if the breaker is incorrectly rated, it could explode when trying to open. If I go to a store and buy a little 20A breaker for a panel, it will also have "10KAIC" on it. That means it can safely interrupt a fault up to 10,000A. At work I've installed 480V HKD breakers that were 100A rated at 65kAIC. If the fault current exceeds that level, it might not safely operate. In a short circuit the miniscule "don't care" values for cable impedance, as well as source impedance, suddenly become very important in determining how much current can flow into a short circuit. Here's a video of a breaker exploding: https://www.youtube.com/watch?v=3dckmSgp1nw&t=431s 
Three-Phase fucked around with this message at 13:37 on Oct 19, 2013 |
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Oct 19, 2013 13:23
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They were outdoors, and that picture was taken a few days after the fire. The covers were raised, I assume, by the FD at some point, and left open. It's the typical flip up cover you see on a lot of 120-480V outdoor stuff.
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Oct 22, 2013 02:20
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I've got a piece of equipment (a servo drive similar to this) that didn't come with a plug but just has screw terminals for power supply. I assume it's intended to be put in an electrical cabinet wired directly into the mains. It runs on 120V AC, so I'm inclined to wire in a plug and just plug it into an outlet. My only concern is the exposed terminals. If they can be covered is this still a code violation? How severe? I think I read somewhere that we need to keep people 3' 6" away if there's exposed terminals. Is that right?
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Oct 22, 2013 17:28
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KernelSlanders posted:I've got a piece of equipment (a servo drive similar to this) that didn't come with a plug but just has screw terminals for power supply. I assume it's intended to be put in an electrical cabinet wired directly into the mains. It runs on 120V AC, so I'm inclined to wire in a plug and just plug it into an outlet. My only concern is the exposed terminals. If they can be covered is this still a code violation? How severe? I think I read somewhere that we need to keep people 3' 6" away if there's exposed terminals. Is that right? Yes, that is certainly designed to go inside a cabinet of some sort. You might also need some other stuff like fuses/branch circuit protection before it's considered a proper installation. You'd have to check the installation instructions to see what else you might need. I don't know whether or not it's against code (I would guess it at least violates OSHA), but it's certainly a very bad idea to leave unguarded terminals out in the open. From a lawyer's point of view, you could be held liable if someone hurts themselves because they licked their fingers and touched the terminals. From a moral point of view, you don't want to be the one responsible for sending someone to the ER because they accidentally brushed up against the terminals while working on something nearby (which is how these things usually happen). You should be able to pop it in to an enclosure pretty easily. Hell, the project boxes at Radio Shack might be big enough if you're trying to be cheap, but your local electrical supply should be able to hook you up with any parts you might need. I'd also be concerned about heat if you're going to put it in to a box. Servo amps will put out some heat, and how much depends on how much power is going through it. Again, you'd have to check the installation instructions to see if they warn about this. Typically they'll give you a heat dissipation number in watts which you can use to run calculations to determine if you need additional cooling. Just to be sure, just wiring a plug to something and running it that way isn't usually up to code. Throwing it in a box will make it touch-safe, but that won't necessarily mean it's safe to use. There's all sorts of things you usually have to check, such as fusing requirements, wire sizing, power requirements, grounding requirements, etc. DaveSauce fucked around with this message at 18:28 on Oct 22, 2013 |
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Oct 22, 2013 18:26
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DaveSauce posted:You should be able to pop it in to an enclosure pretty easily. Hell, the project boxes at Radio Shack might be big enough if you're trying to be cheap, but your local electrical supply should be able to hook you up with any parts you might need. Electrically, it's installed correctly. I'm an EE so I know how to size fuzes, wires, etc. and cleared all that with the manufacturer's engineers as well. I've just never dealt with the physical installation before. Wiring into the circuit directly would require an electrician, which is why I was trying to hook it up as an appliance. Are you saying I can put it in a box and run a plug out of the box?
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Oct 22, 2013 19:20
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KernelSlanders posted:Electrically, it's installed correctly. I'm an EE so I know how to size fuzes, wires, etc. and cleared all that with the manufacturer's engineers as well. I've just never dealt with the physical installation before. Wiring into the circuit directly would require an electrician, which is why I was trying to hook it up as an appliance. Are you saying I can put it in a box and run a plug out of the box? I'm not very literate on appliances in regards to code, so hopefully someone else here is. I don't have access to the NEC anymore since I started working remote to finish a programming project. Most of what I deal with is control panels for permanent installation, and for permanent installations it's very much frowned upon to use cords and plugs (pretty sure it's against code, but I can't cite anything off the top of my head). If it's intended as portable equipment, though, then I believe you should be OK with the plug (again, I can't cite anything, so take this with a grain of salt). What I am saying, though, is that putting it in a box is the least I would do. I can't say it'll meet code just by doing that, because there's a lot to consider regarding cord connected equipment, but it's certainly better than leaving it out in the open. Personally, I'd do it for my own safety, but if this is going to be used by others or otherwise left unattended and energized, I think it's in your best interest to cover it up. As a point of reference, some bigger companies that we've worked with go so far as to require everything INSIDE a control panel to be touch safe.
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Oct 22, 2013 20:17
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You can view the NEC for free if you make an account at NFPA, you only need to pay if you want a PDF. They also use some silly software protection that locks it to you PC but that's quite easily removed.
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Oct 22, 2013 21:25
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Pvt Dancer posted:You can view the NEC for free if you make an account at NFPA, you only need to pay if you want a PDF. They also use some silly software protection that locks it to you PC but that's quite easily removed. I didn't know they offered free access, that's really good to know. I was tempted to yank the "FREE PDF" access key from the hard copy they gave us at work and take it with me when I left, but I couldn't bring myself to do it. But as much as I prefer online documentation (or at least the concept of it), nothing beats a paper catalog with tabs. Both my NEC book and UL508A book were stuffed with tabs for all the sections I frequently referenced. The hardcover "handbook" edition is what all the cool kids have, though. It has tons of explanations and examples to help you figure out what the hell the code is trying to say. Only our hardware engineering manager had a copy of that, the rest of us got the standard paperback. There's also a surprisingly large number of websites that are horrible to use. Siemens, GE, and ABB are the worst. Schneider/Square D is pretty bad as well, but the search function at least works relatively well. Allen-Bradley is pretty good if you know what you're looking for, but I really wish they'd all take cues from McMaster-Carr. I've never seen a website that makes it so easy to find the exact product you're looking for. Almost makes me wish I was a mechanical engineer just so I could use it more often. DaveSauce fucked around with this message at 22:32 on Oct 22, 2013 |
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Oct 22, 2013 22:29
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Siemens has the worst site on the internet, I don't get how they can run a profitable business. My gripe is with legacy documentation, anything older than 10 years is not supported and some Minitrue department remove all information forever. Just toss old PDF manuals in a searchable archive you goddamn fuckers. Schneider low voltage breakers have had at least 50 different types of trip units in the past 30 years and I've come across pretty much all of them. Making SKM models is such a pain in the rear end already, don't make me sleuth for French 50 dpi scans of 1985 manuals please. Please.
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Oct 22, 2013 23:12
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One oddball cord-and-plug tidbit: some medium-voltage motor starters (like 4160V, 350A for a 4000-ish HP motor) have a cord-and-plug attachment inside of them. You would have a 4160V to 120V control power circuit, and there's basically a female plug attached to the control power transformer. The male plug energizes the ladder logic and allows the contactor to open and close. If you want to test the system with the high voltage turned off, you can unplug the male cord, and connect it to an extension cord. There is also generally some position-switch interlocking with the disconnect switch feeding the starter. That and the removable plug make it so you don't accidentally backfeed the bus (120V to 4160V) and kill someone.
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Oct 23, 2013 00:29
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Three-Phase posted:One oddball cord-and-plug tidbit: some medium-voltage motor starters (like 4160V, 350A for a 4000-ish HP motor) have a cord-and-plug attachment inside of them. You would have a 4160V to 120V control power circuit, and there's basically a female plug attached to the control power transformer. The male plug energizes the ladder logic and allows the contactor to open and close. Wouldn't the motor controler/protection system trip on massive undervoltage in that case, and why not use charging springs to test it, just asking.
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Oct 24, 2013 00:10
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Ryand-Smith posted:Wouldn't the motor controler/protection system trip on massive undervoltage in that case, and why not use charging springs to test it, just asking. The systems set up like that are more like a vacuum-bottle contractor than a breaker, so if someone were to unplug power, the contractor would immediately open. To my knowledge there aren't charging springs, and they are not maintained like circuit breakers that have separate trip/close circuits and depending on the application a method of tripping open on loss of control power. As far as the cord and plug, this allows all the ladder logic to be tested, the protective relays to be on and tested, and the contractor itself to be opened and closed without a lot of fuss. One drawback is that those contactors, while sized to accommodate starting of medium voltage (typically 5kV class for 4160V or 2400V) motors, are not sized to interrupt fault currents. So in the systems I've seen they are always used with fuses, and are coordinated so that if the motor protection relay sees a short-circuit fault, it will keep the contractor closed and allow the fuses to interrupt the fault. If the relay tried to open the contactor under a fault, it could destroy the device.
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Oct 25, 2013 00:02
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Turns out A/C is hazardous and we should have D/C https://www.youtube.com/watch?v=34r6RGF2JLA Would anyone like to explain what's going on here?
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Nov 2, 2013 22:00
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So transformers hum. Normal. Today I had a heater controller buzzing itself to the misery of everyone around. Got told not to replace the failing contactor. (Relay. Anyone else call them contactors?) wound up just hand cycling it a few dozen times and adjusting the mountings. Quieter now but still noticeable. Any of you have any sort of tripwires for when stuff should be replaced? We've got a few 1500A molded case breakers that I'm starting to worry about too. The managements view is run it till it fails.
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Nov 2, 2013 22:25
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M_Gargantua posted:So transformers hum. Normal. Today I had a heater controller buzzing itself to the misery of everyone around. Got told not to replace the failing contactor. (Relay. Anyone else call them contactors?) wound up just hand cycling it a few dozen times and adjusting the mountings. Quieter now but still noticeable. Contactors are a specific kind of relay; generally bigger than 5kW and mechanical. When you're talking about industrial electricity, circuits will often have a number of purely electronic "relays" looking for different fault conditions, and will actuate breakers or fused contactors if they detect one.
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Nov 3, 2013 00:17
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Michael Scott posted:Turns out A/C is hazardous and we should have D/C Fault on the transformer drew an arc, the arc followed along the lines like a Jacob's ladder.
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Nov 3, 2013 13:56
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We had a bad wind storm in Montreal last week, and someone filmed this video during the storm. Some reports suggest that the fireball was caused when lightning struck the cables and caused a surge in power. Both the video and sound are
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Nov 4, 2013 23:14
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That's just the arc traveling along the wires from where it started - probably started by an arc flash bridging the wires over where the initial lightshow came from, then air currents (wind, or in the case of a Jacobs Ladder, heat making air rise) pushed the arc along past his house.
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Nov 4, 2013 23:19
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This is neat. 1080 octocopter footage of electric arc furnace
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Nov 7, 2013 23:12
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No matter how many times I see one of these things, I always have a hard time believing it's meant to do that. You could take any electric arc furnace video, rename it "horrible industrial accident", and most people would believe you. Side note: What's up with the orchestral Chrono Trigger music starting at 3:35?  (compare to 2:20) ZorbaTHut fucked around with this message at 15:29 on Nov 8, 2013 |
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Nov 8, 2013 15:27
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 google maps I pass these roadside transmission towers frequently, and I've never figured out what's up with the insulators. Specifically, why the two sides of the tower would have different types of insulators mounted. At first I thought the lines on the right were unused, but after reading the thread I recognized the grading rings. When I stopped to take the picture I noticed the grading rings were split, which seems like it would defeat the purpose. Both sets of lines end up at a substation a short distance to the NW on the map. Note that the photo faces SE, so the weird insulators are on the West side of the transmission towers.
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Nov 8, 2013 22:09
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ZorbaTHut posted:Side note: What's up with the orchestral Chrono Trigger music starting at 3:35? It's from Chrono Cross from PlayStation https://www.youtube.com/watch?v=wMntblDX0Bg There's an SLR camera mounted on that octocopter.
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Nov 9, 2013 05:26
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TasogareNoKagi posted:
One of the circuits could be a different voltage or they added the circuit at a later date and decided to use a different type of insulator.
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Nov 9, 2013 23:01
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Gradient rings allow you to use smaller insulators. The small electrical gradient on the conductor makes it less likely to breakdown, requiring less material.
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Nov 11, 2013 03:59
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Hi, long shot here: A few years ago I saw a video on YouTube where some guys, in Russia or somewhere, approach a full-size (I believe AM) radio transmitter mast outside. They take a branch/stick, bring it close to the tower and start to touch it. An electrical arc forms between the stick and the tower, and the arc gives off a sound that perfectly replicates the music and speech that is being broadcast from the radio station. I think it's due to some sort of short or fault in the tower itself, I don't think that normally happens? Anyway, I lost that video and haven't been able to find it. If anyone knows what I'm talking about I'd like to find it again. 
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Nov 22, 2013 02:27
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Michael Scott posted:Hi, long shot here: grover fucked around with this message at 02:50 on Nov 22, 2013 |
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Nov 22, 2013 02:48
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Michael Scott posted:Hi, long shot here: I was initially skeptical of this. However I thought about it and called my dad: "If you pass a radio signal through an arc, if it's AM, you can get sound from the arc/flame. If it's AM the envelope (amplitude) changes with the signal, so that's how it could work." Wouldn't work with FM, though. Related: Singing flame speaker Tesla coil speaker
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Nov 22, 2013 02:54
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Three-Phase posted:I was initially skeptical of this. However I thought about it and called my dad: 
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Nov 22, 2013 02:59
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So anyway, I asked a while ago if there was interest in seeing one of our 6k6V generators. Sorry it took me so long, but here we go. These photos were taken after an overspeed incident that necessitated taking the rotor out of the generator for an inspection. It's worth noting that the overspeed incident was VERY serious - 1030 rpm when it's rated for 514. By some miracle none of the windings warped. Anyway, on with the show:     
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Nov 22, 2013 10:21
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grover posted:I'm actually more surprised the protective systems didn't shut down the transmitter within milliseconds of the arc occuring. Or that someone was allowed to get close enough to the antenna to make it arc. That poo poo wouldn't fly in the US. I've seen the video, it's kinda cool but incredibly stupid in my opinion. I don't know how you could have the transmitter shut down when the vegetation caused an arc though.
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Nov 22, 2013 11:08
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Two Finger posted:So anyway, I asked a while ago if there was interest in seeing one of our 6k6V generators. Sorry it took me so long, but here we go. These photos were taken after an overspeed incident that necessitated taking the rotor out of the generator for an inspection. It's worth noting that the overspeed incident was VERY serious - 1030 rpm when it's rated for 514. By some miracle none of the windings warped. Anyway, on with the show: Very awesome! What is that, around 100 megs? I'm not sure if I would opt for a brushless exciter, especially for a generator. If it works for you more power to you (pardon the pun). If you don't mind me asking, what facilitated the overspeed incident? Load loss that didn't trip the prime mover?
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Nov 22, 2013 11:31
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Crankit posted:I've seen the video, it's kinda cool but incredibly stupid in my opinion. I don't know how you could have the transmitter shut down when the vegetation caused an arc though. http://www.americanradiohistory.com/Archive-Catalogs/Gates-Harris/Gates-Harris-Cat-No-100.pdf On page 7, describing Harris' 100kW transmitter:  The "crowbar" they speak of is a mercury ignitron switch which, when fires, provides a dead-short between the antenna to ground, to take all that energy away from whatever the fault is. Newer transmitters replace the tubes with transistors, but the concept is still the same: arcs=bad. grover fucked around with this message at 13:19 on Nov 22, 2013 |
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Nov 22, 2013 13:16
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grover posted:There's not supposed to be any arcs, anywhere, ever. Or any vegetation close enough to cause it. High power transmitters generally have protective circuits designed to detect arcing and momentarily shut the transmitter down because arcs = damage, and damage to the transmitter is really expensive. What I meant was, how could you detect an arc at the antenna itself, also I don't understand how an arc(a small one like in the video) at the antenna would be more damage to the transmitter than a dead short.
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Nov 22, 2013 16:03
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Crankit posted:What I meant was, how could you detect an arc at the antenna itself, also I don't understand how an arc(a small one like in the video) at the antenna would be more damage to the transmitter than a dead short. e: here's a photo from inside the old tuning house at WABC; with the energies and voltages (15kV) involved, you wouldn't go inside the tuning house while in operation, or you'd become the arc path.  Apparently, the magnetic fields in the tuning equipment were strong enough that the components vibrated and acted like speakers. Here's a short audio clip: http://hawkins.pair.com/wabcnow/coiltalk.ra grover fucked around with this message at 16:29 on Nov 22, 2013 |
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Nov 22, 2013 16:18
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Interesting stuff, I guess the real reason it didn't shut down then is Old Soviet Equipment.grover posted:(they're rather large at these wavelengths- as in, you can walk around inside them); I think the physical size is more likely due to efficiency and power handling, I think all AM broadcast occurs above the 136kHz amateur allocation and a transceiver I'm planning to build for that is only about the size of a shoe box.
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Nov 22, 2013 16:35
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Worth noting is that the copper pipes in grover's pic are probably the conductors - skin effect uber alles! Crankit, how much power are you going to be pushing? If you aren't producing much, you can get away with a whole lot, ferrites in your tuned inductors, nonresonant antenna lengths, high VSWRs, etc. When you're talking about tens or hundreds of thousands of watts, suddenly a couple percent loss in an inductor matters and you actually have to design the equipment to be naturally resonant at the right frequency without lossy magnetics, which means much larger windings. Conductors of course need to be scaled up either way. I really need to drag the remains of a 10kW 2-30MHz HF band AM broadcast amplifier I bought for $180 out of my storage unit and take some pictures... and then finish dismantling it. I bought it considering using it as a ham HF amplifier but determined that it had been run with an improper load (cracked, arced, burnt ceramic insulators and arc damage all over many of the inductors/variable caps/most of the final stage wiring) and also it came as two refrigerator size chassis and the wiring that connected the two was all torn apart and not documented well enough that I could find a way to put it back together. There was also the problem of actually powering the beast, it wants 3 phase at some ridiculous amount of current.
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Nov 22, 2013 16:54
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Three-Phase posted:Very awesome! What is that, around 100 megs? Could you tell me more about your comment on the brushless exciter? I'm more of an operations engineer than an electrical, I have a working knowledge of how the thing works but the theory is a little hazy to me. This one is about 8 meg from memory, and the overspeed incident occurred because on startup, something got caught in the fuel rack and it could not pull back to maintain running speed. Just kept going faster and faster and it was just sheer luck that one of the other guys was there and pulled the e-stop.
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Nov 22, 2013 18:42
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kastein posted:Worth noting is that the copper pipes in grover's pic are probably the conductors - skin effect uber alles! There's other special cable where they wrap a sheath of conductors around a non-conductive core.
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Nov 22, 2013 18:51
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