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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". At a conference I attended about a year ago this report was presented by the organization doing the investigation. It was hardly relevant to the conference so I didn't pay a lot of attention, but the thing I took away from it was equipment failure without adequate protection. The guy presenting it has being very hand-wringy about whose fault it was. And indeed lucky no one was there, the blast nearly unhinged a steel door and threw shrapnel down a 30m path beyond it. Not testing and even disabling protections is pretty common in small places where they have some facility manager doing the electrical systems on the side. Work is done by contractors who are happy to have it and don't give a gently caress about safety.
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Sep 14, 2012 14:33
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grover posted:I've had excuses from field sites about spare parts being unavailable that I was able to find in about 5 minutes of searching on ebay and get it overnighted to them. Having to resort to ebay is rather an act of desperation, though, and the quality of the parts has to be considered. It's one thing to buy a component that can be tested and verified to work and whose malfunction would not create a serious safety risk, and I'd use a rebuilt 4000A breaker from a reputable shop, but I would never buy a 4000A breaker of unknown sourcing. It's just too dangerous. Breakers and other generic electrical stuff is pretty easy to retrofit with new stuff though. Legacy PLC or DCS really are a blight when it comes to servicing after 20 odd years or so. Usually there's one laptop in the world that has the DOS software license and can interface at all with the PLC. When it breaks or spares run out it's welp, get a new system and no, we can't use the old software.
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Sep 14, 2012 14:40
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I'm not going to lie, I'm a fan of fuses, or at least fuses used in careful conjunction with other protective devices. It's great for preventing nasty catastrophic "blown apart equipment" failures that cost lots of money and time to fix, and reducing arc flash hazards. People whine about having to replace blown fuses when it's easier to snap a circuit breaker back in place. My argument is that if your fuses blow, the system was designed wrong, and/or there's an issue that warrants fixing.
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Sep 15, 2012 01:18
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Lots of action at work today and yesterday testing new equipment - medium voltage. Hopefully all goes well but even with my experience I always am a little nervous and treat equipment with extreme care.
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Sep 18, 2012 09:38
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Meet Top Thrill Dragster Uses electrical energy to power a hydraulic launch system that rockets riders from 0 to 120mph in ~4 seconds, up a 420 foot tower, and back down into magnetic brakes. There's surely a ton of electricity being used to power the launch system. Right now all of the launch energy at the end is being bled off as heat on the braking system. Shouldn't there be some way to capture some of that energy and convert it back to usable electricity that could be fed back into the park's electrical grid? What kind of stuff is involved in setting a grid up where it can have random amounts of energy dumped into it for a short period of time every few minutes? Disclaimer: I know nothing about electricity once you start getting beyond household electrical systems.
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Oct 9, 2012 04:01
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Three-Phase posted:
I was working at a power plant that had just finished commissioning and was still under warranty when we started getting an undervoltage relay trip on one of the generators when we tried to put it online. Both the plant electrician and warranty engineer insisted it had to be the protection and nothing could possibly be wrong with the generator as it had meggered at infinity on the way out of the factory and it was barely a year old. After changing the LVR's around for several days they finally meggered the generator and found two phases had dead grounds on them. Watching them take it out and put a new one in was pretty cool since they had to lift it over two engines on rails. Cost the OEM over $1 mil on a project they were already millions in the hole on. Im just glad the protection was new and worked exactly as it was supposed to, it was a good lesson. It could have been very messy.
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Oct 9, 2012 04:36
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Maniaman posted:Meet Top Thrill Dragster
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Oct 9, 2012 10:38
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The other problem is that capturing energy rapidly creates some issues - supercapacitor banks could be used, but that would be costly and difficult to implement. The other problem is that it might not be all that much energy - not enough to make it practical. It's like someone going around a steel mill and replacing fifty "straggler" incandescent bulbs with CFLs. Over a month, you might save 600kWH, or $90 of electricity. Good for him! That's $90 a month saved assuming a $0.15/kWH. (I already did the math so screw it I know that's really high for an industrial rate.) It sounds good until you realize that your 50MVA arc furnace blows through $90 of electricity in under one minute. Now that power saving doesn't seem that significant. lightpole posted:I was working at a power plant that had just finished commissioning and was still under warranty when we started getting an undervoltage relay trip on one of the generators when we tried to put it online. Both the plant electrician and warranty engineer insisted it had to be the protection and nothing could possibly be wrong with the generator as it had meggered at infinity on the way out of the factory and it was barely a year old. After changing the LVR's around for several days they finally meggered the generator and found two phases had dead grounds on them. They didn't re-megger it at the installation site!?!? Once it's on the floor, we always want to re-megger (and possibly hi-pot or perform other tests depending on the equipment)! New transformer? MEGGER! Replacement motor? MEGGER! Moved existing equipment to another area? MEGGER! Just installed a new section of cable? MEGGER! Possible exposure to moisture? MEGGER! Significant changes to the system? MEGGER! Bringing equipment that was unused for more than a month or two online? MEGGER! Instructed that a system or piece of equipment cannot be meggered or it would create undue hazards to the process, and soforth? Well, don't megger in that case. And there are more than just that, where I am at meggering equipment is pretty much the bare minimum. We don't care how you tested it at the factory, we're testing it here with our people and our equipment. What a shame - I've seen issues myself where a few thousand, hell, even a few hundred dollars worth of time and equipment, doing the job right, prevents tens or hundreds of thousands of dollars worth of failure and downtime. I'd prefer not to go into details about it. Three-Phase fucked around with this message at 00:56 on Oct 11, 2012 |
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Oct 11, 2012 00:22
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I keep threatening my wife with buying a scrambler. It is a carny type amusement ride where you just spin around in a little circle while spinning in a bigger circle. Anyway it takes phase 3 power and I am not getting that where I live. Are phase 1 converters a possibility for this type of electric motor driven insurance liability? http://www.elibridge.com/scramblers.htm Hmm it seems there are some gas powered ones around but I haven't found any for sale. Elephanthead fucked around with this message at 01:49 on Oct 11, 2012 |
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Oct 11, 2012 01:42
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I believe you'd need a rotary phase converter. If you have a decently large 240 service, you should be able to get an appropriate converter. It won't be terribly cheap, but if you're considering carnival rides for your backyard, I'm going to guess that's not a huge concern.  http://www.phase-a-matic.com/RotaryApplicationNotes.htm has some info on sizing. Keep in mind a lot of that type of amusement equipment is hydraulic. Of course I may be wrong, or they may have something more efficient now. Not an electrician, just a DIY that reads too many books.
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Oct 11, 2012 05:14
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some texas redneck posted:I believe you'd need a rotary phase converter. If you have a decently large 240 service, you should be able to get an appropriate converter. It won't be terribly cheap, but if you're considering carnival rides for your backyard, I'm going to guess that's not a huge concern. Serious question: how would you ride and operate it at the same time?
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Oct 11, 2012 11:33
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Can you pull out the three phase motor and replace it with a single phase equivalent at 240V? 10HP is a little big for 240V, but not too bad. See how many RPM it is. If it's a standard four-pole induction motor, it'll be 1800. They listed 12kVA, so that's something like 80% efficiency and 0.8pf? A ten HP induction motor, 240V single phase, and about 1750 RPM will put you back about $1500 plus shipping. Check Grainger - they are one of a few companies where if you have the money, they'll sell it to you. They aren't strictly business-to-business.
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Oct 11, 2012 23:16
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grover posted:Solid state frequency converters are generally cheaper these days. Still gonna be costly. Might be cheaper to buy a cheap used 208V generator and use that. I was thinking have a control station on one of the cars, but you'd need some kind of way to connect it to where the (stationary) motor and control cabinet was. Even then you'd want to have a dead-man's switch (hold to operate) an e-stop, and a backup timing relay. So that would be four wires going to the controller on the car: 1. +24VAC (yeah, I'm gonna be a pansy and use 24VAC for control) 2. E-Stop signal (normally closed E-stop, maintained open when pushed down) 3. Run signal (normally open, spring return to open non-maintained) 4. 0VDC Three-Phase fucked around with this message at 23:38 on Oct 11, 2012 |
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Oct 11, 2012 23:32
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Work update: I need to do some additional simulations in SKM PowerTools today. Looking at transient motor starting on a 7200V bus. I think the bus itself is 1200A, so we're taking about feeding from a 15MVA transformer with I think 8% Z. I've seen some transformers where I'm at that have dual secondaries. So you have H1, H2, H3, X1, X2, X3, and Y1, Y2, Y3. Sometimes it's for phase-shifting, sometimes it's to provide two different voltage levels like 13.8kV and 7.2kV. One of the surprising things in this field (for those thinking about electrical/power career path) is how much writing is involved. Especially in the power field where you need to communicate things to co-workers, especially ones who aren't EEs.
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Oct 16, 2012 10:13
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Three-Phase posted:One of the surprising things in this field (for those thinking about electrical/power career path) is how much writing is involved. Especially in the power field where you need to communicate things to co-workers, especially ones who aren't EEs. There are many flavors and forms of engineering, but I've yet to find one that did not have a significant amount of technical writing involved. grover fucked around with this message at 10:37 on Oct 16, 2012 |
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Oct 16, 2012 10:34
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grover posted:
This is the biggest problem with an uncooperative wife, but I am sure it wouldn't be to hard to have a scrambler party and train people. It seems like carnies and summer part time people operate them with few fatalities now. Surprisingly these can be had in the 15K to 25K range. They seem to last a long time. I was considering using my paid off car for the next 6 years and buying one of these. I have a big flat spot that would be perfect for one. My bigger concern is how safe is one that I can afford. I don't know if there are parts that you can replace to make it safe as new or not. It would probably get old fast but I am sure it maintains its value better then a new car anyway. I would probably sell it after a couple years assuming I don't die. I am emailing my bank's loan guy to see what the rate on amusement park rides is.
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Oct 16, 2012 20:15
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Elephanthead posted:This is the biggest problem with an uncooperative wife, but I am sure it wouldn't be to hard to have a scrambler party and train people. It seems like carnies and summer part time people operate them with few fatalities now. Surprisingly these can be had in the 15K to 25K range. They seem to last a long time. I was considering using my paid off car for the next 6 years and buying one of these. I have a big flat spot that would be perfect for one. My bigger concern is how safe is one that I can afford. I don't know if there are parts that you can replace to make it safe as new or not. It would probably get old fast but I am sure it maintains its value better then a new car anyway. I would probably sell it after a couple years assuming I don't die. I am emailing my bank's loan guy to see what the rate on amusement park rides is. I think the safety PLC system would cost more than the entire ride.  grover posted:Being able to convey technical details tersely is important. It's also challenging to take highly technical material and distill it down for non-technical people, people who very often make very difficult decisions based upon what you write. I've had to do a lot of that this month. What have I explained... -Starting a synchronous motor and why you need armitissiour windings to someone who had no electrical background. Also how broken bars in those windings would impact starting. -Explaining the "garbage-in, garbage-out" problems when trying to do subtransient motor starting simulation where I have really limited information on the equipment I want to model (basically explaining that the simulation is based on tentative data and should only be treated as a really rough guideline) -Explaining that a motor's performance is impacted by the electrical system it's connected to, and vice versa -How a meter takes accurate voltage phase measurements using a corner-grounded, open delta PT circuit -Why I blew two PT secondary fuses (Whoops! Thank god it wasn't the primaries or that would have been a bitch to replace.) Three-Phase fucked around with this message at 22:39 on Oct 16, 2012 |
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Oct 16, 2012 22:32
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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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SeaBass 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 10:40
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Three-Phase posted:I'm not going to lie, I'm a fan of fuses, or at least fuses used in careful conjunction with other protective devices. It's great for preventing nasty catastrophic "blown apart equipment" failures that cost lots of money and time to fix, and reducing arc flash hazards. I am more concerned about single phasing with fuses. However if you are using them in a MV distribution setting for something which isn't a wastewater treatment plant, they are usually much easier to coordinate and provide better protection, as well as cheaper.
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Oct 24, 2012 15:53
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Cheesemaster200 posted:I am more concerned about single phasing with fuses. However if you are using them in a MV distribution setting for something which isn't a wastewater treatment plant, they are usually much easier to coordinate and provide better protection, as well as cheaper. Why not a wastewater treatment plant?
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Oct 24, 2012 19:41
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With single phasing, wouldn't either: 1. An overload relay (smaller motors) detect the excess current and interrupt the motor 2. A relay (Multilin or SEL, larger motors) detects the loss of a phase or a current imbalance and interrupts the motor
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Oct 24, 2012 23:55
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Three-Phase posted:With single phasing, wouldn't either: Assuming those functions are set...
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Oct 25, 2012 20:21
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Anti-Hero posted:Assuming those functions are set... They drat well better be!
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Oct 25, 2012 21:25
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In surgical operating rooms I see "isolation panels" that read out "hazard current" up to 10ma, and most of the outlets throughout the room are connected to it. What is this?
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Oct 26, 2012 02:49
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Three-Phase posted:They drat well better be! And if everything that "drat well better be" was, I wouldn't have all the fun safety videos I just watched. I also wouldn't be trying to convince people that unshielded instrument cable next to VFD motor cables (unshielded too, of course) was an issue.
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Oct 26, 2012 02:49
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squeakygeek posted:In surgical operating rooms I see "isolation panels" that read out "hazard current" up to 10ma, and most of the outlets throughout the room are connected to it. What is this? http://www.24x7mag.com/issues/articles/2007-12_03.asp
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Oct 26, 2012 04:47
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squeakygeek posted:In surgical operating rooms I see "isolation panels" that read out "hazard current" up to 10ma, and most of the outlets throughout the room are connected to it. What is this? No isolated system is ideal, though. There is some leakage to ground through electromagnetic means through the transformer, so if you DID jam that live hot wire into the patient's gut, there would be a small amount of current flow. In this case, up to 10ma. grover fucked around with this message at 15:59 on Oct 26, 2012 |
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Oct 26, 2012 15:56
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Three-Phase posted:With single phasing, wouldn't either: In most cases this would be correct, especially in a MV setting where you would set every protection available for large motors. However, I still work on a lot of older projects with straight magnetic controllers which are not equipped with such relays. Every now and then we get a call about motors burning up because a fuse blew or the utility was being useless again.
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Oct 26, 2012 19:01
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Just got done with the Power PE test today - it was not as difficult as I imagined. The FE was a lot more stressful. Edit - BTW to add to the single phasing conversation, the reason it can still be a problem is because before 1971 the NEC only required Overload protection on two of the three phases to a motor. The loss of a phase on the primary of a transformer serving a motor could lead to a condition where only one phase has high enough current to trip the overload. if this phase happens not to be protected, it will burn up. Read more from Cooper publication. https://www.progress-energy.com/assets/www/docs/business/motor-protection-voltage-unbalance.pdf Allantois fucked around with this message at 21:41 on Oct 26, 2012 |
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Oct 26, 2012 21:24
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So, any thoughts on power grid disruptions due to Sandy? Is it possible for a severe storm like this to impact the grid on a more regional level? (I don't think it is, but wanted to check.) Just did some phase-balance relaying. That was interesting to say the least. Took awhile to fully understand what was going on. Basically you had two CTs, one on either side of the motor. The line-side one is used for metering, but it's placed in series with the one out of the motor going to the neutral. There's a relay element placed between them to ground, and on either side of each CT the reference is ground. Current A + Imbalance Current = Current B It's Kirchoff's Current Law. If the in current equals the out current, like 5A and 5A, the flow through that other element will be zero. However if there's an imbalance, like 5A and 4A, current will have to flow through that element and through the relay and trips on imbalance. Three-Phase fucked around with this message at 22:58 on Oct 28, 2012 |
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Oct 28, 2012 22:53
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It's quite possible. Most disruptions start as trees hitting lines and hurricanes tend to bend the odd tree.
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Oct 28, 2012 22:55
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helno posted:It's quite possible. Most disruptions start as trees hitting lines and hurricanes tend to bend the odd tree. Yeah but I rarely see trees large enough to take down 138kV and larger lines for transmission.
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Oct 28, 2012 22:58
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Here's Dominion Power's power outage map for Virginia. I don't have comparable for the other impacted states, but should be pretty interesting to watch the # of outages explode tomorrow: https://www.dom.com/storm-center/dominion-electric-outage-map.jsp
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Oct 29, 2012 02:54
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Three-Phase posted:Yeah but I rarely see trees large enough to take down 138kV and larger lines for transmission.
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Oct 29, 2012 03:15
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Cleveland has some outages right now in Cleveland. It looks like under 10,000 customers have been impacted. It'll be interesting to see if that map changes through the night. Some areas were hit worse, like Mentor and Lorain. I've got food and water, plus a shitload of AA batteries, these nice little "flameless" candles that are dim but run forever on AAs, and an assortment of 9-hour candles and a candle lantern.
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Oct 29, 2012 22:55
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Whelp. Lost power around 11:00. Going to shut down my UPS to conserve battery power and go to sleep. Updated at 530 am looks like most of Cleveland is down. Three-Phase fucked around with this message at 10:45 on Oct 30, 2012 |
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Oct 30, 2012 03:55
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I just stumbled across this: http://youtu.be/ut5DXxK1dvk?t=8m40s How in the loving christ is this guy alive? 
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Oct 31, 2012 06:13
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stealthdozer posted:I just stumbled across this: It's a very low voltage so it's harmless. You see them fiddling with a transformer to convert regular voltage to something under 10V (I think, didn't watch much of it), it means there's a bit of power behind that low voltage. If you make a short-circuit there will be a few hundred amps flowing and that's causing the sparks.
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Nov 1, 2012 01:29
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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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