|
Have you performed many short-circuit and coordination studies? I'm an electrical engineer in the power industry, though I work more on the utility side of things. I've done quite a lot of protective relay coordination studies for both utilities and industrial clients (typically petrochemical). Some design work, as well. I'll let the OP answer questions as they pop up unless he/she wants me to chime in.
|
#
¿
Sep 3, 2011 23:16
|
|
|
|
| # ¿ Apr 30, 2024 05:58 |
|
|
Three-Phase posted:That sort of swing could be fixed by adjusting down the 2400V transformer secondary tap. (Electricity comes in at 32kV, comes out at 2400V, but you can change the output voltage plus or minus a percent or so.) Did the transformer have an automatic load-tap changer on the secondary?
|
|
#
¿
Sep 3, 2011 23:17
|
|
|
bear shark posted:Does anyone still get DC power transmitted to them or does everyone rectify AC nowadays? HVDC is still used for transmission under special circumstances. While AC transmission is the most efficient for your average transmission line, once you get to REALLY long lines (say, 600 miles or more) HVDC becomes more economic. AC has the advantage of relatively cheap equipment used for transforming voltages to make them suitable for long-distance transmission, but the power losses for AC typically offset the equipment costs necessary for HVDC once you get to those long transmission lengths I mentioned earlier. HVDC is often used as an interconnect between two large systems because it's asynchronous. Some systems when they get large enough become very difficult to sync together. HVDC gets around that as it's all DC anyways, so there is no oscillating aspect to the current. I believe Texas can be considered it's own large islanded system with a couple of HVDC links to the rest of the power grid.
|
|
#
¿
Sep 4, 2011 00:35
|
|
|
Three-Phase posted:I'm assuming you (AH) are also doing things like distance protection relaying and more complicated reliability analysis - looking at what happens to the power system if any specific piece (or pieces) of equipment fail at any time. I do quite a bit of distance protection, specifically communication-based tripping schemes. I also do a good deal of work involving substation control schemes integrating the protective relays with SCADA. I have not seen a system up here where a tap changer did that, but I don't really deal with stuff like that. I'm strictly a design & protection engineer, when I do field work it's typically to test the relays, commission them, or troubleshoot them. Oh, and Multilins are junk. Have you guys had any experience with SEL's motor relay? We spec SEL's exclusively so I'm very familiar with their relays used most often for utilities, but have never messed with their industrial stuff. I hope they are a decent alternative to the Multilin's that most people use. I really hope someone comes out with something that will compete with GE's protection offerings in the industrial industry, I've not been impressed at all with their relay's reliability. fake edit: Have you guys seen GE's new 480V arc-dome product? It's a standalone cabinet that is integrated with existing switchgear to reduce arc flash incident energy levels. It has a dome that is made up of 3 electrodes separated by air. During a fault, photo-sensors detect the light from the event and trigger the electrodes which ionize the air and create a lower resistance arc than the fault, "stealing" all the energy and exhausting it in the dome. Pretty neat stuff, we had some GE sales reps come by the office a couple weeks ago and show us some promotional materials. Anti-Hero fucked around with this message at 04:10 on Sep 4, 2011 |
|
#
¿
Sep 4, 2011 04:04
|
|
|
tworavens posted:How did you get started in the field? I'm currently a student in an Electrical program at a tech college. Anyway they thought us some residential commercial stuff, but I've had the most fun doing industrial and control work. Basically I'm having a hard time finding a place willing to hire me with no experience beyond school. Any tips? That's just how the market is right now. Are you working on your Associate's or a Bachelor's degree? My work progression has been pretty simple. I went to an ABET accredited school for my BSEE and interned one summer for a power engineering consulting firm. They offered me a full time position after I graduated and I've been in the industry ever since.
|
|
#
¿
Sep 4, 2011 04:19
|
|
|
SeaBass posted: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 My experience with industrial coordination is much the same. Fuses coordinating with molded case breakers are incredibly rare. I'm more of a distribution/transmission protection engineer where coordination is generally pretty straight forward. I recently worked on coordinating an industrial installation where all the 480V circuit breakers were UL short circuit rated, and not ANSI rated. The consequence of only performing UL testing is that a hard-coded instantaneous trip must present. If you perform ANSI tests you can dispense with this as you've proved the breaker won't fail to trip on a high enough fault current. The result is that nothing was going to coordinate. It didn't matter if I set the LTPU, LTD, STPU, etc. of the main breaker to coordinate with the feeders, they all had something like a 10 kA non-defeatable inst. function, and the available fault current in the plant was much higher. So I noted in the report that they needed to stop being cheap bastards and replace all this gear with ANSI rated breakers because if they have a fault anywhere in the 480V system it was anyone's guess what was going to clear first. But this is protection, and no one cares about it until it doesn't work.
|
|
#
¿
Sep 28, 2011 23:39
|
|
|
Three-Phase posted:On our equipment we have bus protection relaying, so if there's a fault detected, not only does the bus' circuit breaker trip, but every large machine also connected to the bus simultaneously trips off as well. (I think that's an 86 relay.) That is 87B protection. But what if you have a fault outside of that zone? Like on the cable between the machine and the switchgear bus? That's when proper coordination between upstream and downstream devices is critical, and where the most exposure to mis-coordination lies. This is where overlapping zones for differential protection is very helpful, especially in mitigating arc-flash incident energy levels.
|
|
#
¿
Sep 28, 2011 23:42
|
|
|
You have a 3-phase service in your house?
|
|
#
¿
Sep 30, 2011 17:59
|
|
|
OK, that's what I thought. Thanks for sharing the waveforms; I had always heard that switchmode power supplies were rough looking but I had no idea until now how bad they were.
|
|
#
¿
Sep 30, 2011 18:59
|
|
|
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".
|
|
#
¿
Sep 8, 2012 23:22
|
|
|
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."
|
|
#
¿
Sep 9, 2012 04:46
|
|
|
Three-Phase posted:With single phasing, wouldn't either: Assuming those functions are set...
|
|
#
¿
Oct 25, 2012 20:21
|
|
|
That 480V electrocution video is why you should always meter a circuit even after you think it's isolated. I also hate that the narrator said "440 volts of current passed through his body"...
|
|
#
¿
Dec 15, 2012 23:49
|
|
|
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 |
|
#
¿
Feb 10, 2013 02:56
|
|
|
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.
|
|
#
¿
Feb 10, 2013 03:16
|
|
|
Woops, looks like someone didn't check the pickup current against expected feeder loading.
|
|
#
¿
Feb 10, 2013 06:08
|
|
|
It was either in this forum or another one I frequent when I called this - someone left default settings in the relay and never bothered to adjust them. Massive egg on S&C's face. fake edit: Anti-Hero posted:Woops, looks like someone didn't check the pickup current against expected feeder loading. Hah, close enough.
|
|
#
¿
Mar 29, 2013 05:34
|
|
|
It also reminds of a distribution line sectionalizer. That device can't interrupt fault current. Rather, it has a arming current above a certain amount to remain selective with the upstream recloser, and relies on "counting" the number of reclose operations it detects being committed by the upstream recloser (by counting the amount of times the current drops out) and once a pre-determined of shots have occurred in a window it will open during the last cycle when the recloser has also opened, sectionalizing off the troubled piece of line downstream of it.
|
|
#
¿
Mar 29, 2013 21:53
|
|
|
I'd give their tech support a shout.
|
|
#
¿
Apr 11, 2013 22:45
|
|
|
SeaBass posted:(but always challenge SKM, they really are the bottom rung for these types of programs). My employer maintains licenses on several modeling programs and we have only one client that requires SKM. ETAP seems to be more popular, but as I understand things it's much more expensive. I find ETAP easier to use and doesn't look like dogshit, compared to SKM. However, the fact that a single SKM or ETAP project is actually a folder full of inter-dependent files is pretty annoying. It makes transporting a model between engineers pretty cumbersome. Does anyone have experience with Easypower? We just got a license for that and out of all the programs I've used (SKM, ETAP, ASPEN, and now Easypower) it's the only one that doesn't look like it started in the DOS days. Also an entire project is contain in one file, similar to ASPEN OneLiner but have features more inline with SKM/ETAP. Pretty slick and simple. I'd be interested to hear what other folks think of it. Anti-Hero fucked around with this message at 11:09 on Apr 12, 2013 |
|
#
¿
Apr 12, 2013 11:06
|
|
|
Three-Phase posted:Just remembered this - do you have some impedance between the busses? Circuit breakers by themselves have no impedance, and SKM gets cranky in you do things like connect busses together with no impedance (typically a cable or bus). Does it get cranky, or just flat out refuse to let that connection happen? I think it's the latter. Anti-Hero fucked around with this message at 19:08 on Apr 13, 2013 |
|
#
¿
Apr 13, 2013 03:13
|
|
|
"Skay-duh"
|
|
#
¿
Apr 18, 2013 08:04
|
|
|
SeaBass posted:I finally got around to reading that Superbowl power outage report . . . That wasn't the impression I got. It sounds like the S&C relay has an undocumented instability at the settings it was dialed in at that led to the misoperation, but was not the sole reason for it. It's been awhile since I read it but there was a discussion on it several pages back.
|
|
#
¿
Apr 19, 2013 07:16
|
|
|
Three-Phase, what kind of hoops are you going to have to jump through to get a PE with a BS-EET?
|
|
#
¿
Jul 12, 2013 03:14
|
|
|
You'll be fine. You sound way more interested in the field than I am (I'm referring to your interest outside work), and I muddled my way in to a license. I have faith.
|
|
#
¿
Jul 12, 2013 03:21
|
|
|
|
| # ¿ Apr 30, 2024 05:58 |
|
|
Noctone posted:If you run into more issues I might be able to help by taking a look at our RTS routine for the 311L. Don't have a routine for the 90L, unfortunately. I take it you work for Enoserv?
|
|
#
¿
Mar 18, 2015 17:30
|
|