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Guy Axlerod posted:I'm looking for a second opinion here. I'm working on a repair technician course for a piece of equipment that is dual-fed 480VAC and 230VAC, each three phase. Read #1: http://www.lewellyn.com/pdf/os_pdf/Arc%20Flash%20Myths%20and%20Misconceptions.pdf Sums it up better than I can.
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Sep 14, 2011 20:48
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DaveSauce posted:On that note, how common is proper coordination? It is not as common as it should be, but with OSHA being more assertive about assessing arc flash hazards, design engineers will be more diligent about protective device evaluation and coordination. Or they can pay me to do it for them  Honestly, for all of the reports I have reviewed, less than half are done correctly and that is because the systems are so small there is little room for error. The larger the system, the more room for something to get overlooked or not considered as a fault current contribution.
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Sep 28, 2011 00:13
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PPoison posted:Why would it be left to float and why could it take any voltage? What's the theory behind it, the mathematics? In certain applications where power continuity is critical, and ungrounded delta is used so that a single phase-to-ground fault won't take down your entire system. The trade off is that ungrounded deltas tend to be pretty noisy (transient voltages, harmonic disturbances, etc.) so if sensitive equipment is connected to this source, some filtering or other power quality improvements need to be made. These are also used in the maritime industry because you don't have an available ground, or one that you would want to shunt many, many kA (kilo-amps) of fault current to anyway.
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Jan 6, 2012 20:32
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Three-Phase posted:Can the utility company tell you what the line-line and line-ground fault current levels are? (Oh wait, maybe you ARE the utility company...) I've never had much luck with utilities providing that specific of information as their systems are constantly changing, but most should be able to provide you with X/R ratios at your point of common contact and then you can go from there. I'm really surprised SKM will produce garbage results like that. We give you a prompt and let you know we're going to disregard the calculation because no protective devices are present, so therefore an IEEE 1584 calculation will be worthless. Probably one of the reasons they aren't NUPIC certified like we are, but I digress.
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Jan 17, 2012 00:40
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zapradon posted:I just found this wonderful thread, and have read nearly all of it (I think.) Any mechanical loads on the buses feeding those 9395s?
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Feb 22, 2012 01:16
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zapradon posted:No telling. It was a client site that apparently has each customer installing their own UPS's (a nightmare scenario, it sounds like to me.) Yeah, it can definitely end up being a mess. Site managers typically don't have much beyond what was originally installed. You might have better luck with the customer's electrical contractor for getting as-built one lines.
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Feb 22, 2012 18:44
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alwayslost posted:I'm a junior EE student and I recently got an internship at the local utility. The job is kind of lame (analyzing large amounts of data for improving substation performance) but hopefully it will be my foot in the door to getting a design-type job. My internship last year was in integrated circuit design, so I'm kind of all over the map right now. What is the market like for power engineers right now (my full-time job hunt starts this fall)? It seems to me like a solid industry to get into in the United States, since energy is a hot thing right now and you can't really outsource our utilities. The semiconductor industry, on the other hand, seems like a sinking ship in the United Stats, where only the super elite can find jobs with the titans like Intel, Texas Instruments, Qualcomm, etc. Power engineering is a very good field. Between updating the existing infrastructure, adding capacity for the ever increasing demand for more power and implementing new technologies, there is more work than the existing workforce can handle. Getting a MSEE is a good idea, especially if your employer will pay for it.
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Apr 20, 2012 19:57
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Looking at the equipment (signal cabinet), you'd probably be at a category 0 most of the time, possibly category 1 if you're exposing yourself to live conductors. This is with the assumption that the available fault current is under 25kA and the upstream protective device will clear in two cycles. When in doubt, have someone do a study.
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May 16, 2012 01:30
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I've only seen the corona at a 500kV sub after a good rain on a very humid day. Even then it was pretty faint, but still cool to see (and hear).
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May 30, 2012 18:08
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Three-Phase posted:Wow, I just found a video of 500kV corona at a substation! It's beautiful! Yep, that's pretty much what we saw.
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Jun 2, 2012 23:10
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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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Three-Phase posted:
This is the biggest problem I had with clients. They wouldn't want to pay for a site visit so they'd send in crappy data and then ask us to make assumptions. Very frustrating. Glad I'm no longer in that industry.
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Oct 17, 2012 04:10
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stealthdozer posted:I just stumbled across this: That looked like it was from a car battery or something similar.
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Nov 1, 2012 05:20
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I'd put under arc flash reduction a site survey and arc flash analysis using computer aided tools. You don't have to get too in depth about it, but mention that in complex electrical systems it is the only way to get a somewhat accurate picture of the arc flash hazards.
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Jan 27, 2013 19:02
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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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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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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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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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Having worked for one of SKM's competitors and knowing how these software packages work, here are my brief statements: - ALWAYS RUN loving POWER/LOAD FLOW!!!! This is how you determine if your design/model is feasible in the real world. If poo poo don't converge, you hosed up! - Trust me, the Chinese/Indian PhDEEs who code the software know their poo poo more than you do. They may not be able to do a project, but they will loving own your rear end on theory. Bottom line, if there are issues, it is most likely on you, not them. (but always challenge SKM, they really are the bottom rung for these types of programs).
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Apr 12, 2013 06:42
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Pvt Dancer posted:What competitor did you work for? I used to work for EDSA (now Power Analytics) on the DesignBase product. Unfortunately the company is going down the shitter. Once the VP of engineering and consulting retires in the next year or two, I think the company will fold.
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Apr 13, 2013 03:13
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I finally got around to reading that Superbowl power outage report . . . One of the worst forensic reports I've ever seen. Basically saying a lot of nothing because the guy doesn't know poo poo about relays or being a protection engineer. S&C is not high end stuff like SEL but hopefully they have enough in their legal budget to sue the poo poo out of that Palmer clown.
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Apr 19, 2013 06:52
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Three-Phase posted:The only one-lines I could get were the European ones. If I still worked for EDSA I'd hook you all up with a copy of the software.
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Apr 19, 2013 06:56
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Frozen Horse posted:The highest voltage circuit I've been around lately was a bit more than that, but only about 100 mA. On the other hand, it was a 100 mA beam current at 7 GeV or so. At that point, it's a beam of electrons in ultra-high vacuum. What capacitors do you use for the linear accelerator?
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Jul 14, 2013 02:17
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drk posted:Unfortunately the article Ars is citing at the Wall St Journal is paywalled, so its not clear if anyone was injured. Say what you will about the NSA, but I also hope no one got injured. It could be a capacity problem, it could be lovely operators, it could be a poorly designed facility but most likely it is a combination of all of the above.
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Oct 9, 2013 19:17
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IOwnCalculus posted:It's probably just that, but I'm going to hope that it's really sabotage. Yeah, that would be a lot cooler than them just being morons.
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Oct 9, 2013 19:30
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edit: nm, I want to see how this turns out
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Dec 23, 2013 19:38
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If the protection engineers did their job, none of those catastrophic events should happen. The fault should be isolated but, I can't speak for every situation.
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Jul 24, 2014 07:44
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I used to work at GA as a technical sales engineer in the capacitor group. Where did you get the cap and what are you using it for?
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May 12, 2015 23:13
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atomicthumbs posted:I took apart a flashlamp-pumped Nd:YAG medical laser (a New Star Lasers Cooltouch II) that was due for recycling and I'm using it for destruction I knew that cap looked familiar. Sorry, can't help you.
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May 13, 2015 05:19
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Some contractors found this fine piece of work the other day. 
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Aug 24, 2017 23:44
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Noctone posted:Looks to me like the contractor ran short on the larger conductor and spliced on several smaller conductors to finish the run. That's our working theory right now. They're tracing it out but we find stuff like this about once a week.
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Aug 25, 2017 02:45
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