|
I'm a commercial electrician. I love all the stuff that happens on the upstream side of the green boxes on the pads outside. I am also curious about the coordination stuff; It seems to me like you CAN just put a 200kA fuse with 5k let-through in front of 5kA stuff and call it good, but I don't know for sure. I got to tour a decent sized GE co-gen plant about a year ago. I can't remember their output in MVA, but it was a fairly large gas-turbine direct-coupled to a hydrogen-cooled genset with the exhaust feeding a steam turbine coupled to another hydrogen-cooled genset about 200 yards away. The switchgear room in there was neat. I've also been to the building (but not inside) of the Artesia DC-DC link that connects the Eastern grid to the Western grid. Apparently the thyristor bank looks like a giant scientist's apparatus that feeds some plumbing nightmare. The DC bus is just a bunch of 18" copper rods going through the wall, and it looks like oversized plumbing pipe. I wish I could have gone inside. Question time: do you guys still follow the NEC, or is there another standard? I know there are a bunch of sections for "over 600V, nominal" and whatnot, but they're so very short, comparatively.
|
#
¿
Sep 30, 2011 11:01
|
|
|
|
| # ¿ May 3, 2024 06:37 |
|
|
helno posted:For the guy wanting to run a 3 phase motor off of single phase you need to buy a variable frequency drive unit. It will generate the 3 phase you need out of house power and will even give you variable speed. This. VFDs are the way to go. Any kind of phase converter in this modern era is just silly. There are some chinese-made $100 units that will take any input power and output any output power as long as you want 1 or 2hp. 12-480V DC, AC, single- or 3-phase on the inputs and outputs. Very nice units, and cheap. I don't know if they explode or not, though, but I pitch them extensively for the local plant operators who accidentally bought 3-phase 480 gear and all they've got is 208Y or 208 open delta or something. Plus, you can get them with internal current limiting and disconnecting means, so you only need one box instead of three (overcurrent protection, disconnecting means/isolating means, controller). Something from way back in the thread that I wanted to comment on is the concept of a "disconnect." A true disconnect is a load-breaking switch. Most industrial stuff only uses isolating switches, which cannot operate under load. "Conditions of operation and maintenance which ensure only qualified personnel can work on the equipment" means that coordinated shutdown of the machine means the isolating switch isn't opened under load. Typically, even the OCPD isn't used as a disconnect, either, unlike in your house, where the maintenance guy will just flip the breaker off for your A/C when it's running before fixing it.
|
|
#
¿
Sep 30, 2011 23:58
|
|
|
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.
|
|
#
¿
Feb 7, 2013 19:52
|
|
|
I hope someone can answer this here. For electric trains, how does distribution work? I think I saw a couple of taps of to transformers along the train ride. Do those transformers have to worry about being in phase? I know this train line is a couple hundred km long, so frequency has to drift along the length of the cable, right? Is a few hundred km just not long enough to worry about?
|
|
#
¿
Mar 3, 2013 13:59
|
|
|
helno posted:We have hundreds of temperature measurements. Hundreds in the stator. The rotor temperature is measured indirectly with some voodoo magic (pyrolysate collector). I would be interested in such a post. I'm a big fan of huge generators and instrumentation in general, and the specifics of an installation would be really cool.
|
|
#
¿
Apr 27, 2013 19:24
|
|
|
Captain Foo posted:I didn't even know "dry steam" was a thing Also hot steam and cold steam. Also the temperatures of the water at various points, and whether it's expected to be boiling there or not. You can have 600C water in one point, and everything's OK, and 25C water somewhere else that really should be boiling there.
|
|
#
¿
May 2, 2013 17:25
|
|
|
Crankit posted:I live in the UK and in our fuse box the first set of fuses says 415V 80A/100A, should I be frightened of arc flashes from them when they fail? What's the difference between the neutral and ground pins in a plug? I was told by a school physics teacher (some years ago) that a shaver socket is safer than a regular power outlet because if I came into contact with a wire I wouldn't be completing the circuit and so wouldn't receive a shock, is that true? Fuses are designed to keep arcs in, so no problem there. The neutral pin goes back to the source of your power, typically the transformer on the pole. The ground pin goes to the earth at your panel. Usually there's a bond between the two there. The fundamental difference is that the neutral pin is designed to carry current under normal circumstances (it's the second wire of a complete circuit) where the ground pin should only have current/voltage on it in a fault condition. Going from memory here, but shaver sockets in the UK are usually powered by isolation transformers and are therefore ungrounded. So accidentally touching one wire doesn't give a complete circuit to anything, as the transformer isn't connected to ground. Touching both wires will still shock you, but maybe not kill you because the transformer is power limited (I think). Other parts of the world use a GFCI (ground fault circuit interruptor). If you touch one wire and complete a circuit to ground, the outlet senses the ground fault current and shuts the power off.
|
|
#
¿
May 7, 2013 17:59
|
|
|
Three-Phase posted:Is that 690/400 or 1200/690? The US Navy's ships use a 69/120 ungrounded Y power system. Each circuit is 120V and has a fuse in each leg. A single ground fault opens the leg, turns on a light in the fuse panel, and the system faulted keeps running at 70V. It's very fail-safe and battle hardened, and takes multiple faults to totally fail. The generators are also rated down to 18% power factor. 1800MW at 95% pf, 600MW at 18%. Impressive movers.
|
|
#
¿
May 19, 2013 23:10
|
|
|
Three-Phase posted:So 50kW is 60A at 480V. That is big compared to, say, a house, but fairly small for a whole hospital. It's moderately large for a single piece of patient equipment, but I'd bet the chiller motors are 150-300A each, and there are usually a couple of them. HVAC is a way way bigger power expense than patient equipment, followed by lighting, then pretty much everything else.
|
|
#
¿
Jul 8, 2013 15:48
|
|
|
He's probably got three-phase power coming into the building, and a squirrel shorted one phase to ground, so the delta-wye transformer in the basement is working on open delta, so there's one leg that's super low. I'm 95% sure that square box on the pole is a power quality monitor or a smart meter relay/concentrator.
|
|
#
¿
Jul 11, 2013 15:21
|
|
|
Three-Phase posted:I was looking for switchgear videos and did come across this one ( This is exactly my job. The lovely camaraderie, the descriptive language, and the excellent pipework and wonderful wire terminations. Also, coming in on Saturday, with half the crew, and one dude walkin around doin nothin, but he buys the pizza, so it's OK.
|
|
#
¿
Jul 18, 2013 22:22
|
|
due to some coarse language). The install work looks pretty nice and they seem to have a fairly cohesive crew (nobody telling anyone to go f themselves). If this video gives you pause, be aware this isn't that unusual, especially at a factory. (However things are much less lax in many places now due to both legal concerns and workplace violence concerns.)
|
Three-Phase posted:Speaking of splices - I've seen kits that are "cold shrink", where the material is under tension, and you can unwind a piece of material that causes it to compress down. I could see where this would be useful at facilities that are really picky about hot work permits, but I've also heard that this is a little more hokey and inferior to splices and terminations that use heat-shrink covers. Cold shrink is a direct replacement for heat shrink, and is just as good. The 3M guy that came by our jobsite sold both kits, and said it was up to us which to use. We used cold shrink in the summer and heat shrink in the winter. Never had a splice, tap, or termination fail that I know of. Both kits are basically the same except for the last step.
|
|
#
¿
Jul 18, 2013 22:40
|
|
|
Three-Phase posted:Just a quick question - am I correct in assuming if you own a residence, in an area that is zoned for standard houses, no matter how much money you offer the power company they cannot/will not do something like installing a separate three phase transformer (120/208, 277/480, or 347/600) into your home to supplement your existing Edison 120/240? In most suburbs, there's only one phase per street. The subdivision will have 3-phase run by it, and only one phase will go down each street. It's not unheard of for people to find property where a couple of the single-phase lines get close and get an open delta. I saw one not too far from my house recently. Looked like a standard property, but with two transformers on the pole and four buried lines going down. I'll try to get a picture at some point. Two odd-sized transformers up there really caught my eye. He probably just bribed someone at the utility, or he or his cousin works there.
|
|
#
¿
Oct 9, 2013 01:49
|
|
|
MrYenko posted:My last renters insurance policy covered space debris, unless it was powered by a nuclear reactor or RTG. Ha! My rental policy covers nuclear events not part of an act of terrorism. However, it specifically excludes fires resulting from acts of war. Policy writers must have an awesome job sometimes.
|
|
#
¿
Oct 12, 2013 20:31
|
|
|
|
| # ¿ May 3, 2024 06:37 |
|
|
Noctone posted:Those dudes must be living in their own tiny little world then, because I've never heard anyone use "megger" as a lowercase noun/verb to refer to anything other than insulation resistance test sets/testing. It's like Kleenex and facial tissues. Yeah. Even when we had a Megger(r) mega-ohmmeter and a Megger(r) hi-pot tester, only the mega-ohmmeter was the megger, the other one was a hi-pot. In the same way, the "fluke" was the fluke 77 multimeter, even though our ground rod tester was made by fluke.
|
|
#
¿
Jun 13, 2015 04:34
|
|