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It looks like most of the grid is back online. It looks like there is a combination of bad factors, including states pulling more power then they were supposed to. Under the right conditions and the wrong engineering, (and even sometimes with the right engineering) an electric grid is a house of cards.
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Jul 31, 2012 19:48
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You're posting a bunch about dealing with arc flash hazard as it's something that's pretty widespread in the US, it may surprise you that in Europe it's hardly even recognized. I've been doing hazard assessment studies for a few years now (first with a big switchgear supplier, now have my own consultancy business), mostly for US companies that try to force Europeans to work according to NFPA 70E. I spend a lot of time negotiating between US and European safety people to get something workable out of it. Most of the experienced electrical engineers I talk to dismiss it out of hand, saying that because of better (IEC) switchgear design it never happens. Usually within the minute they start talking anecdotes of near misses and (ex) colleagues getting burned, but hey, they made a dumb mistake! So I spend half my training session trying to convince these people that yes, it does happen and because you work for a US company now you better get ready to deal with it anyway. On the other hand, I think switchgear *is* a lot safer here due to good shock prevention and shorter infrastructure lifecycle, so 99% of the time the risk really is lower. Once a US engineer literally told me "safety alone is never a reason to replace switchgear", which is something that will get you in prison here if you were to repeat that to a judge after an accident. The remaining 1% is where people get badly injured and that seems hard to instill. I think the one thing that unites US & EU electrical engineers is their hatred for PPE and overly conservative HSE managers. I'll keep an eye on this thread, and maybe can answer some questions about European stuff. My experience is mostly with the analytical side of industrial power systems (I have delicate hands only suited for typing up reports), but I've seen a lot of low and medium voltage distributions, with a little bit of high voltage, for everything from datacenters to offshore wind farms.
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Aug 5, 2012 00:47
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Pvt Dancer posted:You're posting a bunch about dealing with arc flash hazard as it's something that's pretty widespread in the US, it may surprise you that in Europe it's hardly even recognized. I've been doing hazard assessment studies for a few years now (first with a big switchgear supplier, now have my own consultancy business), mostly for US companies that try to force Europeans to work according to NFPA 70E. I spend a lot of time negotiating between US and European safety people to get something workable out of it. That's sad and bizarre. I'd expect the europeans of all people to be concerned with worker welfare and safety. One argument is that you can save money not just in protecting the people, but an arc flash can completely trash equipment. If you can fundamentally mitigate the arc flash, you can improve both worker safety and prevent costly downtime. Where I work, with NFPA 70E, in a lot of cases you need Level-2 PPE to open the cover to even a 120/208V panel. A lot of people are chagrined by that. However on big electrical systems, you can get pretty fearsome arc flash levels even on low voltage panels.
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Aug 5, 2012 01:19
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Arc Flash as a "big deal" has been a fairly recent phenomena in the US; most of it has been on the books for a long time, but it was never really prioritized. Europe will come around to it eventually, I think. I don't like the way grounds are dealt with in much of Europe, either. It just seems wrong routing grounding conductors via a different path than the current-carrying conductors. Three-Phase posted:Where I work, with NFPA 70E, in a lot of cases you need Level-2 PPE to open the cover to even a 120/208V panel. A lot of people are chagrined by that. However on big electrical systems, you can get pretty fearsome arc flash levels even on low voltage panels. grover fucked around with this message at 01:43 on Aug 5, 2012 |
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Aug 5, 2012 01:34
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Wait, isn't 20A at 120v what my house runs on? Cause I've reset those mofos barefoot a few times. 
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Aug 5, 2012 01:45
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FrozenVent posted:Wait, isn't 20A at 120v what my house runs on?
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Aug 5, 2012 02:14
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Three-Phase posted:Also, if a major part of the grid was damaged, there are often reciprocal agreements where if there's a bad disaster in area A, the linemen from areas B, C, and D converge to help out in A. One of my co-workers said awhile back when there were really bad storms, he saw a convoy of a dozen utility trucks heading down the highway to the affected areas.
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Aug 5, 2012 03:21
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Three-Phase posted:That's sad and bizarre. I'd expect the europeans of all people to be concerned with worker welfare and safety. The main problem is that it doesn't even exist as A Thing in most regulations and standards here. There's a test performed on medium voltage air insulated switchgear that demonstrates that with everything closed up an internal arc will be neatly contained, and equipment manufacturers brag about how safe it is. So what happens with all their untested (low voltage) switchgear or once you start opening panel covers to do some voltage testing? Yeah.
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Aug 5, 2012 21:06
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I have a 2kw AC to DC rectifier for the purpose of powering a Xenon projector lamp. The input requirements are 3 phase 240v AC 60hz at about 18amps . I only have residential 200 amp 240v split phase. I heard from someone once that it was possible to create a capacitor bank to generate a 3rd phase and drive the rectifier. Rotary converters are out since there is apparently too much ripple. Could you provide any insight as to how to assemble such a circuit?
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Aug 7, 2012 03:30
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Panaflex posted:I have a 2kw AC to DC rectifier for the purpose of powering a Xenon projector lamp. The input requirements are 3 phase 240v AC 60hz at about 18amps . I only have residential 200 amp 240v split phase. I heard from someone once that it was possible to create a capacitor bank to generate a 3rd phase and drive the rectifier. Rotary converters are out since there is apparently too much ripple. Could you provide any insight as to how to assemble such a circuit? If it's just a "dumb" diode rectifier, you may be able to just hook up 2 phases and run in a derated (1.2kW) condition. No promises on the ripple current, though; it won't be as clean as if the rectifier had balanced inputs since it's designed to smooth a 360Hz ripple and you'll actually have 240Hz. Would help if you added new capacitors in parallel with those already in the rectifier, though. E: series is not parallel grover fucked around with this message at 12:27 on Mar 4, 2013 |
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Aug 7, 2012 22:52
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Panaflex posted:I have a 2kw AC to DC rectifier for the purpose of powering a Xenon projector lamp. The input requirements are 3 phase 240v AC 60hz at about 18amps . I only have residential 200 amp 240v split phase. I heard from someone once that it was possible to create a capacitor bank to generate a 3rd phase and drive the rectifier. Rotary converters are out since there is apparently too much ripple. Could you provide any insight as to how to assemble such a circuit? Wait, 2kW? The math doesn't seem to work right for the voltage and current you specified: 240 * 18 * 1.73 = 7473W (assuming 100% efficiency and unity PF)
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Aug 10, 2012 10:51
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I saw three "PIKE" electrical service trucks with North Carolina plates in Miami today. http://i.imgur.com/c5z7F.jpg full size What do the "? GROUNDED" stickers (on all three trucks) mean? Are they a safety thing to remind workers to check if the truck is grounded before doing something dangerous? Are there some kind of placards or magnets that go over them when the truck is grounded? The "If you lived in your truck you'd be home" sticker was only on that one truck.
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Aug 28, 2012 19:49
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Cocoa Crispies posted:I saw three "PIKE" electrical service trucks with North Carolina plates in Miami today. Its a safety reminder, when line trucks work on energized lines, they will install a ground. I've never seen any line workers put magnets/placards on their truck when its grounded. They are required to hold pre-job briefings to go over any dangerous activities they might encounter on their specific job.
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Aug 28, 2012 23:30
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It seems like it would be dangerous to put a sign on your truck saying "Yep, its grounded!" It would create a false sense of security if you ever forgot to take the sign down.
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Aug 29, 2012 00:43
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http://www.maib.gov.uk/publications/investigation_reports/2011/qm2.cfm Take a read of the accident report. I'm interested to know what you guys think from a professional electrician's perspective, as opposed to my own as a marine engineer's.
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Sep 4, 2012 03:55
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Two Finger posted:http://www.maib.gov.uk/publications/investigation_reports/2011/qm2.cfm Cool, I'll give that a read tomorrow and give you a power system engineer's perspective.
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Sep 4, 2012 04:12
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Basically my perspective is haha holy gently caress they hosed up good and it's a goddamn miracle no one died.
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Sep 4, 2012 04:17
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I'm hardly an engineer, or really anything beyond a DIY guy with just enough knowledge to be dangerous. But it really sounds like their lack of giving a poo poo about "why is this thing eating caps so often?" combined with a faulty monitoring system, no real test protocols, "oh look another loving false alarm", and woefully insufficient logging = how the gently caress did this not happen sooner? I mean, any company with expensive stuff is going to log serial #'s and how often parts are replaced, and one would hope they'd monitor trends.. unless it belongs to HF banks on a cruise ship apparently. So how long are large capacitor banks like that supposed to last (even land based)? The document suggests 20 years, I see some stuff that's easily twice my age every time I drive anywhere though. randomidiot fucked around with this message at 05:32 on Sep 4, 2012 |
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Sep 4, 2012 05:22
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Did you read through to the part where a steel door got blown off its hinges The photo is amazing
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Sep 4, 2012 05:44
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I'm going to have to read through that carefully - looks very interesting from just a skim.
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Sep 4, 2012 10:33
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some texas redneck posted:So how long are large capacitor banks like that supposed to last (even land based)? The document suggests 20 years, I see some stuff that's easily twice my age every time I drive anywhere though. Actual life of capacitors depends on the electrolyte and other conditions- heat decreases their operational life of some designs by quite a bit (many electrolytic caps have their operational life cut it in half for every 15F over 77F, just like VRLA batteries). They'll generally give warning signs before failure, in the form of reduced capacitance and swelling, but you have to be looking for it because it generally isn't readily apparent without specific instrumentation. They apparently were looking, as the seven other caps had been replaced pre-emptively, but in this case, the protective circuit for the faulty capacitor had failed with the display showing an unlikely (but seemingly ideal) 000mA current imbalance and nobody thought to look any deeper. What most likely happened was swelling of a polypropylene insulator caused a contact to break loose, which caused electricity to spark across the gap, locally vaporizing some of the dielectric oil. Vaporizing the oil deep in the tank in the absence of air would not cause it to ignite, but while oil is a very good insulator and lets you place high voltage conductors closer than you otherwise would be able to, vaporized oil is not- get the bubble in a bad spot and it would arc between terminals like a full-on short circuit. At that point, BOOM! QM2 Report posted:Deterioration of the capacitors in the HF was monitored by measuring the current imbalance between the capacitors in each of the three phases. I've seen harmonic filters fail before and turn into charred masses, but this one had a lot of power behind it! You can see the capacitor broke it's mountings and blew several feed upwards when it exploded:  QM2 Report posted:The probable conditions that existed just before the accident: oil weeping or spraying out from the failing capacitor casing; 11kV voltage across the three phases; and the subsequent release of flammable gases from the capacitors, were ideal for an arc-flash event to take place. The melted corners of the copper bus bars indicate that arcing did take place between the phases, and it is therefore possible that the explosive noise heard by the crew members was due to the shock waves produced by the rapidly moving hot air emanating from the arc column. It's very fortunate nobody was in the room when it blew. As to the cause, the report is full of finger-pointing. The cruise line is blaming the manufacturer for shoddy capacitors, but the manufacturer is blaming the cruise line for damaging them with a lot of transient surges. Or, as the report more diplomatically put it, "The fact that the unit did fail catastrophically indicates that either there was a system side problem overstressing the capacitor or that the capacitive elements could not perform to their stated rating." grover fucked around with this message at 13:40 on Sep 4, 2012 |
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Sep 4, 2012 12:14
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grover posted:It's very fortunate nobody was in the room when it blew. As to the cause, the report is full of finger-pointing. The cruise line is blaming the manufacturer for shoddy capacitors, but the manufacturer is blaming the cruise line for damaging them with a lot of transient surges. Or, as the report more diplomatically put it, "The fact that the unit did fail catastrophically indicates that either there was a system side problem overstressing the capacitor or that the capacitive elements could not perform to their stated rating." It is nothing but luck that this happened at 4am as the watches were changing over - that means that most of the crew were asleep, and the engineers were all in the control room. This could have gone so much worse. Anyway, one particular point to note, is this:  During drydock, for whatever reason, the protections were not tested, so it was not established that they were nonfunctional. Thanks for your post, Grover. Pretty interesting to get another perspective - obviously my study involved some electro-theory but only pretty limited, as we have electricians to do the bulk of it.
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Sep 4, 2012 20:10
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Two Finger posted:Anyway, one particular point to note, is this: Also damning is that one of the other capacitors failed a few years prior with an imbalance of 1250ma, an imbalance level well in excess of the 400ma alarm point and 800ma automatic trip point, and mere 50ma shy of the 1300ma it's calculated to arc over and explode! You'd *think* someone would have taken action to check & fix the CT and relay circuit at that point, yet nobody did. During the investigation, this CT was found to have an open primary coil and had been completely non-functional for literally years before the explosion. So, no protective circuits tripped until the exploding capacitor bank tore the electrical bus bar off the other capacitors in the bank and the subsequent arc flash triggered a different protective relay. grover fucked around with this message at 21:14 on Sep 4, 2012 |
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Sep 4, 2012 21:07
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On a ship, at 11kV even in equipment that was not meant to be opened/exposed when live, wouldn't it have made sense to put some kind of shrinkable insulating cover over the terminals? I know people do that for 15kV-class equipment. The problem is it would have been a real bitch for servicing. Two Finger posted:Anyway, one particular point to note, is this: At least they didn't lie about the testing or just hammer in checkmarks without actually doing the checks.
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Sep 4, 2012 22:12
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grover posted:Yeah, that's pretty damning. I'd be willing to bet it was actually discovered- or at least suspected- to have failed, but the tech doing the PM didn't want to deal with it. "Chief, there's something not right with the aft HF bank." "Sure, we'll check it." "No, seriously, I've been keeping an eye on it for a while and there's something not right." "I checked it, it's fine." "Can we get it looked at in dry dock?" "No, it'll take too long."
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Sep 4, 2012 23:13
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grover posted:Failure of small non-replaceable electrolytic caps embedded into circuit boards is one of the leading causes of old-age death of computers and consumer electronics. You mean I'm not the only one who's lost motherboards to knockoff caps? Two Finger posted:"Chief, there's something not right with the aft HF bank." This sounds extremely likely.
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Sep 5, 2012 00:00
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some texas redneck posted:You mean I'm not the only one who's lost motherboards to knockoff caps? 
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Sep 5, 2012 00:04
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grover posted:I lost 3 loving motherboards at work to that poo poo. You'd think the contractor responsible would have switched suppliers or something, but, no, they bought a 10 year supply in bulk or something The monitor on my desk at work right now is a nice LCD that I pulled off the junk cart. It had been pitched because it was flicking on and off in about 1 second intervals. After unsoldering and testing the caps in the power supply pcb, I found the one that had failed. The replacement capacitor came from a computer power supply that was kicking around the closet. Now it works.
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Sep 5, 2012 04:53
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Neat video I recently found: Pulse closing versus reclosing When you're at home and you see your lights go out, then come back for a short fraction of a second, and then go out entirely, it's probably a recloser.
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Sep 8, 2012 13:37
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Three-Phase posted:Neat video I recently found:
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Sep 8, 2012 16:41
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grover posted:How does pulse closing work? Clearly does a fantastic job of limiting the fault energy vs a traditional style. No clue. The recloser let a lot of cycles through, maybe it has SCRs that only fire and allow less than one cycle through?
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Sep 8, 2012 18:50
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Reclosers are just a vacuum bottle (to make/break fault current) that uses TCC curves to trip, and pre-programmed intervals to close (usually 2 or 5 seconds). Lots of reclosers have a pole-mounted control cabinet, which is really the brains of the operation. I'd imagine the Intellirupter is using a vacuum bottle, but it's control is waaay more sophisticated. Once it's tripped, it sends through a 5ms "pulse", and based on some measurements, it can sense a permanent fault or if it was just temporary. Not sure how it's injecting the pulse - whether it's closing the vacuum bottle, or if it's using something else. However, if you've got a tree branch phase-to-phase, when a recloser closes in after tripping, it's letting enough fault energy through to blow a branch off and the fault clears. The Intellirupter doesn't let nearly as much energy through, and it so can actually incorrectly say the fault's been cleared (even though the branch is still there). It'll close back in and hold for a while, it'll fault and trip again. That said, it's a really cool piece of equipment, and S&C certainly did their homework. Shame many utilities are just using them as automated switches.
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Sep 8, 2012 22:08
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I'll have to read through that accident report in more detail, but as a system protection engineer I closed the report as soon as I read that they hadn't been keeping up with their protection testing. I'm sure there is plenty of finger pointing to go around as to what exactly caused the caps to fail, but the fact that the protection was inoperable is just deplorable. I can't count how many times I've dealt with a client who hasn't tested a certain protective device in ages and just disables it because "it keeps throwing up alarms so we just pulled it out of the circuit/opened the DC breaker feeding it".
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Sep 8, 2012 23:22
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Anti-Hero posted:I'll have to read through that accident report in more detail, but as a system protection engineer I closed the report as soon as I read that they hadn't been keeping up with their protection testing. I'm sure there is plenty of finger pointing to go around as to what exactly caused the caps to fail, but the fact that the protection was inoperable is just deplorable. I can't count how many times I've dealt with a client who hasn't tested a certain protective device in ages and just disables it because "it keeps throwing up alarms so we just pulled it out of the circuit/opened the DC breaker feeding it". I've witnessed where this has happened and it sucks. In my designs, protective equipment always have some kind of failsafe configuration, where if the protective equipment stops functioning, the machine stops functioning as well. I've seen designs on systems where this isn't done for whatever reason and it blows my mind. (With the exception of some special systems where the user would rather destroy the equipment than have it shutdown, a "melt before fail"/fire pump/battle short approach.) The inevitable engineering finger-pointing stage also really, really sucks for everyone involved. It's painful the way people treat these things. You've got a 50A fuse protecting a motor with 40FLA (approximate 80% sizes, I need to check the NEC). The fuse blows. They put in a 60A fuse. That blows too. They put in a piece of copper pipe section. Then the upstream breaker trips and you have smoke and a fire alarm going off. If anyone who is reading this is not an engineer in the field or familiar with this stuff, here's the takeaway: Fuses blow and breakers trip for a reason. Same for protective equipment. There's really no such thing as a "random trip". Disabling protection or ignoring warnings out of convenience is dangerous. Three-Phase fucked around with this message at 04:04 on Sep 9, 2012 |
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Sep 9, 2012 03:52
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Three-Phase posted:
It's like back in the old days when you still had fuses in a 120V household circuit panesl..."if it keeps blowing just put a penny in."
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Sep 9, 2012 04:46
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Something I would never buy: 4000A Circuit Breaker Via E-Bay New in box? Used? Who knows.
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Sep 9, 2012 14:21
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Three-Phase posted:No clue. The recloser let a lot of cycles through, maybe it has SCRs that only fire and allow less than one cycle through? Did a little research this morning: http://www.sandc.com/edocs_pdfs/edoc_060671.pdf EPRI posted:Pulse closing is accomplished by a sub-cycle close-open of the switchgear contacts. In fact, the contacts are closed for less than 2 ms. Current flow is established as the contacts close, but the contacts open before the first current zero crossing, at which time the current flow is extinguished. Another important part of the technology is the ability to close the interrupter contacts at a specified point on the voltage wave. The ideal point-on-wave closing angle must generate enough current to measure and analyze, while still keeping the energy let-through into the fault as low as possible. grover fucked around with this message at 14:42 on Sep 9, 2012 |
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Sep 9, 2012 14:35
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Three-Phase posted:Something I would never buy: The plant I work at still uses old GE PLC 5s and some really old Provox I/O. The only way to find parts for these is on eBay.
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Sep 9, 2012 16:08
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Meow Meow Meow posted:The plant I work at still uses old GE PLC 5s and some really old Provox I/O. The only way to find parts for these is on eBay.
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Sep 9, 2012 16:15
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Meow Meow Meow posted:The plant I work at still uses old GE PLC 5s and some really old Provox I/O. The only way to find parts for these is on eBay. I can completely understand getting PLC/RIO components (that are not life/safety or plant integrity related) on Ebay.
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Sep 9, 2012 16:20
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