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The other problem with arc flash and some things like short circuit analysis is that changing the system can invalidate past data. Like if you have a unit sub with this transformer: 4160V Delta 480 Y - 500kVA, 8%Z And replace it with: 4160V Delta 480 Y - 1MVA, 6%Z You're going to need to re-run your arc flash and short circuit calculations downstream. So if you have a sticker on equipment that lists the incident energy, those are all going to have to be updated.
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Jan 27, 2013 19:31
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Three-Phase posted:The other problem with arc flash and some things like short circuit analysis is that changing the system can invalidate past data. Like if you have a unit sub with this transformer: I think both the NFPA 70E and the IEEE 1584 state that any significant change in the electrical system warrants a re-study. I might have stayed in that field had it not been a royal pain in the rear end to convince the bean counters that these studies are important.
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Jan 28, 2013 02:04
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SeaBass posted:I think both the NFPA 70E and the IEEE 1584 state that any significant change in the electrical system warrants a re-study. I might have stayed in that field had it not been a royal pain in the rear end to convince the bean counters that these studies are important. That's what a few of those YouTube videos are for.
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Feb 2, 2013 00:29
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Or you can get comical situations like my last job where management understands the necessity of arc flash and coordination studies but doesn't understand the technical complexity of them, and thinks a junior engineer with very little power systems experience can just pick it up in their spare time, at no cost, as an ancillary skill.
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Feb 2, 2013 01:12
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Probably too early to ask this, but what caused the outage at the superdome during the superbowl?
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Feb 4, 2013 05:09
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grover posted:Probably too early to ask this, but what caused the outage at the superdome during the superbowl? Hate to post a crappy image macro here, but it's the only version of this I've seen:  http://nbcsports.msnbc.com/id/50689277/ns/sports-nfl/ NBC posted:Auxiliary power kept the playing field from going totally dark, but escalators stopped working, credit-card machines shut down, and the concourses were only illuminated by small banks of lights tied in to emergency service. grover fucked around with this message at 16:33 on Feb 4, 2013 |
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Feb 4, 2013 16:19
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That is pretty cool how some of the signs are able to hold their output for a fraction of a second. Big capacitors in switching power supplies and all.
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Feb 4, 2013 22:26
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It looks like a relay (probably a switchgear main feed) tripped. They should have been able to check the logs, see what caused the trip, clear the fault condition and then reclose the relay (after shutting stuff down so they can bring it back up to keep a stable load). I wonder if this will prompt electrical redesigns on stadiums to make them resemble mission critical facilities with fully redundant power infrastructures like data centers.
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Feb 5, 2013 05:16
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I read today that a feeder was upgraded prior to the SB due to concerns about age to the feeder and how it could handle the load. Knowing how contractors work, they probably just made sure that the feeder was properly sized and gave no shits about device coordination or a protection scheme. Welp, that bit them in the rear end. Unfortunately this will give no credence to protection/power system engineers who specialize in making sure this stuff doesn't happen.
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Feb 6, 2013 05:12
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SeaBass posted:Welp, that bit them in the rear end. Unfortunately this will give no credence to protection/power system engineers who specialize in making sure this stuff doesn't happen. It did make for a pretty interesting Superbowl. Does anybody know what the lighting that stayed on in the stadium used? is it common in industrial/large scale settings to run normal lighting off a different mains feed, e.g. would they have a high voltage and a low voltage mains feed and all the big things would run off the high voltage, or would they have generators for emergency lighting?
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Feb 6, 2013 08:44
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BuzzVII posted:It did make for a pretty interesting Superbowl. The lighting left on wasn't distributed evenly enough to be emergency lighting. It's likely that everything that stayed up was being fed from a different distribution board and whatever tripped wasn't the main feed coming into the building (or they have multiple feeds into the building, which is allowed as long as you put signage up to that effect).
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Feb 6, 2013 23:01
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Papercut posted:The lighting left on wasn't distributed evenly enough to be emergency lighting. It's likely that everything that stayed up was being fed from a different distribution board and whatever tripped wasn't the main feed coming into the building (or they have multiple feeds into the building, which is allowed as long as you put signage up to that effect). Large facilities like that typically have multiple feeds due to voltage drop, existing service feeds aren't large enough to handle the entire load, etc.
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Feb 7, 2013 05:58
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SeaBass posted:Large facilities like that typically have multiple feeds due to voltage drop, existing service feeds aren't large enough to handle the entire load, etc.
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Feb 7, 2013 11:32
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grover posted:Why wouldn't they use a single feed (two transformers for redundancy), and distribute at 4160V or some other low MV? Once a place gets big enough, the power company doesn't "stock" transformers and switches large enough, so a place will get a couple of service drops. The Superdome probably has one or two 11kV drops to perhaps six 4160 substations around the place. If one of the 11kVs failed, then there would be some load shedding, same as if one of the 4160s dropped. Looking at google maps, I think there are two feeds into the place, a great big one by the chiller plant, and a smaller one over on the east side.
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Feb 7, 2013 19:52
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It appears a faulty protective relay on one of the main feeds between the switchgear and stadium caused the superbowl outage- it detected a cable fault that didn't exist, and unnecessarily opened a key main breaker. http://www.entergy.com/news_room/newsrelease.aspx?NR_ID=2670
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Feb 8, 2013 16:57
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The stadium's only 30MVA. That's not a large load, but I could see where they'd put it on multiple systems to distribute the load and provide some degree of redundancy. At 69kV that's only 250 amps. 125 if they can get a connection to the grid at 135kV. Three-Phase fucked around with this message at 00:27 on Feb 9, 2013 |
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Feb 9, 2013 00:21
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I almost wonder if there was really a problem with the relay at all. Replacing it sounds like the kind of thing you do when you have a ton of public scrutiny hanging over your head and a bunch of powerful people who want answers. e: I mean really, if they had a false trip on the relay, why did it take so long for anyone to figure that out? I gotta imagine the maintenance staff are competent enough that the relay logs are the first thing they would check. At any rate the whole thing is amusing to me, especially since I just spent the bulk of this week testing some SEL 351s and 587s for a substation. Noctone fucked around with this message at 02:46 on Feb 9, 2013 |
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Feb 9, 2013 02:39
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I doubt we're going to get good anwsers about this, at least not soon. It's not like we have any three-line diagrams to look at. I want to learn a little more about the GE 745 (transformer protection - includes protection on transformers with multiple secondaries) and the 750 (feeder protection). Worked a bit with 4/3/269 Multilins for motors. One of my minor gripes about the 469 is that it doesn't have configurable fail-safe relays. Like the R1 (TRIP) form-C trip contacts held closed and then released during a trip condition. The 469 can't do that, but other Multilins can. It only energizes the R1 on a trip condition. If you want to be somewhat failsafe, you can use the R1 contacts with the R6 (HEALTH) form-C contact, because that's held closed as long as the relay doesn't have a problem, so that gives you failsafe protection that will dump the motor if there's a problem with the relay. (Assuming you have a system where the motor and the infrastructure is worth more than the process.) Plus the Multilin software that talks to the relay can be a little "touchy" when you are commissioning it, like entering forced values can be clumsy. Some of the folks at work despise the GE relays. I haven't had issues with them. The SELs have a pretty awesome warranty and a good price, and I've been told that a lot of time if you send in a relay that fails outside of the warranty, they'll still take a look at it and even replace it. Three-Phase fucked around with this message at 06:28 on Feb 9, 2013 |
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Feb 9, 2013 06:25
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Noctone posted:I almost wonder if there was really a problem with the relay at all. Replacing it sounds like the kind of thing you do when you have a ton of public scrutiny hanging over your head and a bunch of powerful people who want answers. e: I mean really, if they had a false trip on the relay, why did it take so long for anyone to figure that out? I gotta imagine the maintenance staff are competent enough that the relay logs are the first thing they would check. My guess is that the problem will be with the relay logic programming and not the relay itself. I think this fault occurred in the new switchgear that was installed in December. A problem like this should have been sorted out during witness testing.
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Feb 9, 2013 07:07
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So a question on careers. I've been doing industrial controls work for about 5 years. I started at a machine builder doing the controls for that out of college, and now I'm working for a panel shop that does both OEM and end user work. We design, program, and build panels, and also offer turnkey solutions for a wide range of customers/applications, which is really nice because I get to learn how to control all sorts of different equipment. As far as things to do with a Comp Eng/Elec Eng degree, where does controls rank? I'm a huge fan of programming, as that's my background and currently what I like doing. I'd rather program a PLC than design a panel or do power distribution. I'm likely going to be moving in the next year or so, so I'm trying to figure out if I should stick with controls or if I should try to move in to some other career path. For reference, in college I always thought I'd be doing firmware/microprocessor programming. PLC programming is something I rather enjoy, but I always want to be working with hardware of somesort, whether it be electrical or mechanical. One thing I've noticed is that where I am (twin cities), controls is a pretty small world. Everyone knows just about everyone else. I was always under the impression that controls was kind of a default thing to do for sparkies, but I'm kind of learning that it's a much smaller world than I originally thought. I'm kind of curious where this might take me in 10-15 years and if I should stick with it or jump ship at the next convenient opportunity. I don't really know what sort of things I can be doing down the road if I stick with the controls path. I don't know if I want to work at a panel shop forever, but I don't know if I want to go back to a machine builder or try to get a job as a controls engineer for a plant or something.
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Feb 9, 2013 18:34
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Controls is pretty huge and it's only going to get bigger. I can't think of a single controls engineer I know that has ever struggled to find work.
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Feb 9, 2013 18:50
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Yeah, controls is a pretty niche field, but it's also a hugely in-demand field and one where you really no-poo poo need to have a specialist in it to do anything remotely complicated. There's a lot of money in it if you're really good at it.
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Feb 9, 2013 20:50
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Three-Phase posted:Am I missing anything good?  facial expressions as when that came up in a regional firefighter training session.
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Feb 9, 2013 21:44
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Yeah, that is a good one to mention. As far as careers go, be sure to look for and join professional societies. They are great networking opportunities, plus you get to spend time with and learn from people who share the same passion for electricity and controls.
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Feb 10, 2013 00:02
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GWBBQ posted:Do a section on the special hazards of substation fires. Focus on the thermal decomposition products of transformer oil and why HF is called bone-seeking acid. I don't think I've ever seen so many HF reacts insanely powerfully with calcium. The first thing it does is attack your nerve endings, causing not pain, but numbness- many people don't even know they've been injured by it until hours later, when it reaches the bone and causes insanely excruciating pain, which can only be treated by multiple of injections of a calcium solution deep into the flesh to at least somewhat counteract the acid. To this day, any time I see teflon lab equipment, I flinch. grover fucked around with this message at 02:43 on Feb 10, 2013 |
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Feb 10, 2013 02:05
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Three-Phase posted:Some of the folks at work despise the GE relays. I haven't had issues with them. The SELs have a pretty awesome warranty and a good price, and I've been told that a lot of time if you send in a relay that fails outside of the warranty, they'll still take a look at it and even replace it. To put it bluntly, the GE multilin relays are dog poo poo. It wouldn't surprise me if the relay that misoperated during the Superbowl was a multilin. We've been advising our clients to retrofit, when possible, with SELs. In the last month I've seen two multilins, from two completely different lines, crap out and need replacing. They also cost about twice as much as an SEL with a warranty a fifth as good. edit: grover posted:I had to deal with pure HF in the lab in college; always scared the piss out of me. Even the vapors were enough to dissolve glass. It will eat through normal plastics, glass and even ultra-pure quartz containers; we had special teflon equipment for HF, which was just about the only thing it wouldn't destroy, and only ever kept it in the vapor hood. Wasn't HF the acid used in Breaking Bad to dissolve bodies? To me it always looked like the process as shown in the show as more indicative of lye decomposition rather than HF. Anti-Hero fucked around with this message at 03:01 on Feb 10, 2013 |
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Feb 10, 2013 02:56
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Noctone posted:I almost wonder if there was really a problem with the relay at all. Replacing it sounds like the kind of thing you do when you have a ton of public scrutiny hanging over your head and a bunch of powerful people who want answers. e: I mean really, if they had a false trip on the relay, why did it take so long for anyone to figure that out? I gotta imagine the maintenance staff are competent enough that the relay logs are the first thing they would check. I've worked maintenance for a railway in Australia specialising in substations. I can give limited info on protocols from our company, which may or may not be similar to the New Orleans authority If the relay sensed a fault and tripped, the first thing the operator will do in the control room is determine whether the fault caused a lockout (MTM - Multiple trip Manual) or just a pain trip (MTA - Multiple trip Automatic). A MTM fault requires field staff to do a series of tests and clear the lockout at the substation manually. MTM faults are major faults. MTA is a minor fault like a short term overcurrent. If there is no lockout the operating centre will try to reclose the breaker, if it opens again during a specific time period then it may lockout and field staff will be called out. I am assuming that like when we have special events there are staff located at important locations to rectify the fault, so would the New Orleans authority. The first 10 or so minutes would be purely a conversation with the field staff and the operator on the nature of the fault, staff would then go and find the faulty equipment and fix it. Once a problem is fixed there would be a procedure in place to bring the feeder back online which can take time. So after 35-40 minutes after the fault occuring power was restored and a futher 10-15 minutes needed to warm up the lights again. As I said before, I work in the industry and in another country. I do not have any inside knowledge about the workings in American power distribution. This is just a guess.
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Feb 10, 2013 03:02
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Anti-Hero posted:To put it bluntly, the GE multilin relays are dog poo poo. It wouldn't surprise me if the relay that misoperated during the Superbowl was a multilin. We've been advising our clients to retrofit, when possible, with SELs. In the last month I've seen two multilins, from two completely different lines, crap out and need replacing. They also cost about twice as much as an SEL with a warranty a fifth as good. That's too bad, really. I'm probably in the "Multilin is OK" boat since I haven't been burned yet. Sort of like a "Well PayPal never froze my account" situation. Am I correct that the SEL relays are far more versatile in how you can program? I've also seen a system where the SEL protecting the bus had a sort of interlocking where the trip curves for the branch circuits partially overlapped the trip curve for the main protecting the bus, but if a relay downstream detected a problem and began to trip, it would send a signal to the feeder relay saying "Hey, you're seeing 10PU current because there's a fault downstream of me. Don't start to open, I am already opening it." Not sure of the term for this setup, but it allowed for faster response times but prevented coordination issues caused by overlapping trip curves. Big Steveo posted:As I said before, I work in the industry and in another country. I do not have any inside knowledge about the workings in American power distribution. This is just a guess. Sounds about right. I've seen places where the switchgear have a lockout switch on the breaker compartment. Something trips, it opens the breaker and the 86 goes into the tripped positon, so the breaker cannot just be closed again without someone resetting the relay (throwing the switch). Modern SCADA systems (computers that monitor the power grid) will give an indication to say "Hey, this relay activated and this breaker opened without us telling it to open." You'll get a horn in the control room and the event will print out or be listed on a (or multiple) screens. Three-Phase fucked around with this message at 03:19 on Feb 10, 2013 |
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Feb 10, 2013 03:09
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SEL relays are very versatile in programming, but that also makes them much more complex. You can define latches and variables and use them with all sorts of equations in order to implement advanced functions bordering what you'd need a PLC for. I'm in a rush right now but later I'll expand on this with some examples. That's a fast-bus trip (or zone-interlocking) scheme. I've programmed a couple of those using SEL-351S relays, SEL-2100 logic processors, and using Mirrored Bits communication protocol. The traditional way of implementing that scheme was using traditional DC I/O but the newer relays can do it all over comms.
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Feb 10, 2013 03:16
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Big Steveo posted:I've worked maintenance for a railway in Australia specialising in substations. I can give limited info on protocols from our company, which may or may not be similar to the New Orleans authority Nah that sounds about right. I was just saying the story sounded fishy and like some people were trying to cover their asses. And now that the relay manufacturer is saying that somebody hosed up the settings, I'm inclined to think I was right.
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Feb 10, 2013 05:09
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Woops, looks like someone didn't check the pickup current against expected feeder loading.
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Feb 10, 2013 06:08
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"Oh wait, are those CTs 1200:5 or 600:5?"
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Feb 10, 2013 23:52
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Or were the 1200:5 with two turns through them?
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Feb 11, 2013 00:01
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Ok. I laughed at this despite a man being electrocuted. Not because a man was electrocuted, but because of the way everything was portrayed. Oh, I wish you could cut cables that large that quickly and easily with a pair of gardening shears. Rubber gloves towards the end of the video - no outer covering. Wearing these gloves will probably offer little to no protection if you make contact with the >69kV overhead wires. (Especially with no hot stick, outer glove, and soforth.) The highest I've seen gloves rated are like 15kV and you'd be insane to touch energized wires under 15kV without a hot stick, even with gloves insulated at that level. WARNING - violently pulling off cables while live may result in arc flash. Three-Phase fucked around with this message at 16:23 on Feb 16, 2013 |
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Feb 16, 2013 16:05
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Excuse me sir, but I believe there may be a short.
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Feb 20, 2013 22:39
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I'm sorry 911 dispatcher, but I can't hear you over my factory exploding.
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Feb 20, 2013 23:17
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"I need the biggest fire extinguisher you have... ... no, that's too big." Three-Phase fucked around with this message at 11:56 on Feb 21, 2013 |
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Feb 21, 2013 11:47
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Not an industrial electricity question, but I figured you guys would be able to help me out nonetheless. I recently found an article that demonstrates wiring three car batteries in series and using them as an improvised stick welder. Seems like it would be pretty useful to be able to weld with limited supplies in certain situations. However, some of the comments warn about the potential for the batteries to explode when used like this. Is there any truth to their warnings and if so, why would using batteries to weld cause them to explode?
door Door door fucked around with this message at 05:44 on Feb 22, 2013 |
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Feb 22, 2013 05:37
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Probably because the current draw is potentially so large (basically like short-circuiting the battery, particularly if you gently caress up and weld the electrode into the surface) that the battery will heat up so much that the electrolyte will boil, and enough pressure will build up to explode the casing.
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Feb 22, 2013 07:12
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I think that John nailed it. The battery can send out a tremendous amount of current, but only safely in short bursts. My guess is that with a modern lead-acid battery, the acid would probably boil out the top, but if it's really sealed, it could explode the battery. If you were in a life or death emergency had HAD to do this, I would keep people far away from the batteries, wear whatever sort of protection you had available, and only weld in very short bursts. And have the batteries disposed of afterwards. Have some base ready too to neutralize acid in case the battery does boil or explode. I've seen a large UPS battery (or "jar") with a transparent casing that boiled, but it didn't explode. I'd try welding with batteries before I'd try welding with a transformer secondary (not from an arc welder). wargamerROB posted:Not an industrial electricity question, but I figured you guys would be able to help me out nonetheless. Actually, there are a lot of industrial applications that need batteries that are similiar to, but much larger than, car batteries. - UPS power sources - DC backup power for operating switchgear Medium voltage (>600V) circuit breakers typically require a separate power source to open and close. Specifically, to charge up springs inside to slam the breaker closed, and snap the breaker open. So if you have a power outage from the utility, you have a backup that can safely open circuit breakers instead of leaving them closed. If you're in a substation, there'll be a little building that contains protection relays and battery banks so that the big SF6/blast breakers can be operated or at least brought to a safe state. The ABB AMVAC uses a large capacitor, and it can be programmed to automatically open after a power failure is detected. Three-Phase fucked around with this message at 12:27 on Feb 22, 2013 |
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Feb 22, 2013 12:20
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