Ask me about industrial electricity 2: electric boogaloo

The Something Awful Forums > Discussion > Ask/Tell > Ask me about industrial electricity 2: electric boogaloo

tworavens: Oct 5, 2009

rainwulf posted:

Question again for anyone: does anyone know/work with the high current low voltage DC stuff used in aluminium refineries? I have heard of stories revolving around the current being so high that its magnetic fields can actually bend stuff, but i would like to hear from an expert.
Also what kind of rectifiers do they use for that? Or is it some other form of low voltage high current generation systems?

I worked at one for two years. We had some pretty intense magnetic fields, not enough to bend anything. But enough that you could break a bone getting your hand caught between a large bolt and the field. Parking a truck or forklift over the wrong spot would keep you from staring it back up, it would also kill the engine of some vehicles. I know it used to be worse and the did some kind of magnetic correction or something that I really didn't understand to save power. I could find out more because my father works there still.

We ran at 1008 VDC for each of the three lines, and 140,000 amps for each line.

Each aluminum pot ran at 4.2 VDC normally. It got fun when we had pots leak, we would get some scary pretty scary arcing. Each pot was filled with cryolite and a number of other chemicals. We would dump bauxite in the side and break it in with a jackhammer attached to a crane. Each pot produced about 100 pounds of aluminum an hour.

We sucked it off in a big ladle that we poured into transports. The transports got hauled up to a cast house where they made several sizes of billet and small ingots.

They used four large rectifiers for each line that I believe where diode type. They could run each potline on two of the rectifiers. They would fail from time to time, and sometimes explode. The lead time is huge on that kind of thing, so they don't want to run the risk of having to shut down as it costs millions to restart.

edit: I worked at an Aluminum smelter. Did you mean a bauxite refinery?

# ? Dec 6, 2011 07:11

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# ? Apr 16, 2024 07:02

Vanagoon: Jan 20, 2008; Best Dead Gay Forums
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tworavens posted:

I worked at an Aluminum smelter.

A bit off topic, but have you ever heard of Aluminum referred to as being "congealed electricity" because it takes so much power to smelt it?

# ? Dec 29, 2011 06:01

Three-Phase: Aug 5, 2006; by zen death robot

Vanagoon posted:

A bit off topic, but have you ever heard of Aluminum referred to as being "congealed electricity" because it takes so much power to smelt it?

I had heard about people trying to see if there was a way to somehow "reverse" the smelting to store and regenerate electricity. Sounds odd though.

# ? Dec 29, 2011 22:16

Nerobro: Nov 4, 2005; Rider now with 100% more titanium!

that's utter nonsense. That's like using trying to break down an electroplated coin to extract the energy. .... people need to take more chemistry courses.

# ? Dec 29, 2011 22:52

Groda: Mar 17, 2005; Hair Elf

Three-Phase posted:

I had heard about people trying to see if there was a way to somehow "reverse" the smelting to store and regenerate electricity. Sounds odd though.

You aren't of proposals (there was something on Slashdot a while ago) to use aluminum-oxidizer batteries as a way of storing surplus electricity via aluminum production?

# ? Dec 29, 2011 23:01

grover: Jan 23, 2002; PEW PEW PEW

There may be some way to recapture some of the thermal energy from the smelting process, but nowhere near what was consumed in the first place.

# ? Dec 29, 2011 23:15

Nerobro: Nov 4, 2005; Rider now with 100% more titanium!

grover posted:

There may be some way to recapture some of the thermal energy from the smelting process, but nowhere near what was consumed in the first place.

Yes, scrape aluminum into a powder, combine with iorn oxide and expose to high heat.

Use energy released to produce power.

But that's not exactly easy to do.

# ? Dec 29, 2011 23:55

grover: Jan 23, 2002; PEW PEW PEW

Nerobro posted:

Yes, scrape aluminum into a powder, combine with iorn oxide and expose to high heat.

Use energy released to produce power.

But that's not exactly easy to do.

That's chemical, though, and pointless. I was referring to recovery of heat from the giant red-hot cauldron of molten aluminum and slag as it cools.

# ? Dec 30, 2011 00:40

Nerobro: Nov 4, 2005; Rider now with 100% more titanium!

I would expect there is. A combination of good thermal barriers and say... letting the cooling piles generate steam ;-)

# ? Dec 30, 2011 00:55

Three-Phase: Aug 5, 2006; by zen death robot

Groda posted:

You aren't of proposals (there was something on Slashdot a while ago) to use aluminum-oxidizer batteries as a way of storing surplus electricity via aluminum production?

Yeah, that's what I was talking about. The way I initially described it does, as the other poster said, sound like utter nonsense.

I heard something on Quirks and Quarks about it awhile back when they were talking about massive energy storage systems for power grids.

# ? Dec 30, 2011 01:38

Frozen Horse: Aug 6, 2007; Just a humble wandering street philosopher.

Three-Phase posted:

Yeah, that's what I was talking about. The way I initially described it does, as the other poster said, sound like utter nonsense.

I heard something on Quirks and Quarks about it awhile back when they were talking about massive energy storage systems for power grids.

It's not that crazy. Chemically, it's similar to a rechargeable alkaline battery, except that it uses aluminium instead of zinc. This change increases the voltage per cell in the battery, but requires non-aqueous electrolyte conditions. So, you use your solar/wind/etc. intermittent source to charge these batteries when there's an excess of power, and then discharge then through an inverter in lean times. For grid storage, I think a sodium-sulfur cell would be better, since size and weight are less of issues than the cost per kWh stored. I also suspect that the future of this sort of thing is best done in a decentralized fashion, with moderate-sized battery banks allowing large customers to buffer their demand.

# ? Dec 30, 2011 21:24

grover: Jan 23, 2002; PEW PEW PEW

Three-Phase posted:

Yeah, that's what I was talking about. The way I initially described it does, as the other poster said, sound like utter nonsense.

I heard something on Quirks and Quarks about it awhile back when they were talking about massive energy storage systems for power grids.

Ah, OK, I see what you're talking about now; I thought you were trying to recapture energy "lost" during smelting. Given the energy density, though, I can see how it would be useful as a chemical battery, too. But since the end state is a solid, it would be very difficult to do outside of a lab.

# ? Dec 30, 2011 22:39

Groda: Mar 17, 2005; Hair Elf

grover posted:

Ah, OK, I see what you're talking about now; I thought you were trying to recapture energy "lost" during smelting. Given the energy density, though, I can see how it would be useful as a chemical battery, too. But since the end state is a solid, it would be very difficult to do outside of a lab.

I think the idea was for ~~Iceland~~ locations with access to large amounts of undeveloped hydropower, which are too distant from any meaningful demand to transmit it conventionally, to be able to export electricity.

Iceland and others (Hoover Dam was a similar situation in its day) are of course already doing that in a way, by smelting imported aluminum ore and exporting the refined (can't think of the word) metal.

# ? Dec 30, 2011 22:46

Frozen Horse: Aug 6, 2007; Just a humble wandering street philosopher.

Groda posted:

I think the idea was for ~~Iceland~~ locations with access to large amounts of undeveloped hydropower, which are too distant from any meaningful demand to transmit it conventionally, to be able to export electricity.

Iceland and others (Hoover Dam was a similar situation in its day) are of course already doing that in a way, by smelting imported aluminum ore and exporting the refined (can't think of the word) metal.

Yeah, at the moment the metal is worth more than the electricity you could get out of an aluminum-based battery in most places where you would want electricity. If fossil fuels were to become more expensive or if fossil fuel users were required to store their emissions somewhere other than the atmosphere, the situation could change. Then instead of tankers taking oil from Arabia to wherever and returning in ballast, you'd have container ships taking aluminum from Iceland and bringing aluminum oxide back again.
In the pacific NW, there used to be a lot of aluminum smelting (thus why Boeing set up shop there), but the local demand for electricity makes in uneconomical.

# ? Dec 30, 2011 23:57

PPoison: Nov 11, 2011

Please tell me about artificial neutral points... Let's say we have a wye-connected three-phase transformer with the neutral point connected to earth and a phase-to-phase voltage of 400VAC and 230VAC phase-to-neutral (a common configuration in Europe). Now let's get rid of the earth connection. If the loads are balanced we will still have 230VAC phase-to-neutral, the neutral now being called an artificial neutral point since it hasn't got a fixed reference point as the earth connection has been disconnected. Now, if the three-phase loads are unbalanced due to excess output on one phase, what effect will this have on the neutral point and the voltage on the other phases with respect to the neutral?

I've heard all the time that the voltage on a single phase with respect to the artificial neutral point will vary with the difference of loads, but I can't really understand why. According to KCL the current will be zero in the middle point of the wye regardless of the loads. What am I missing?

# ? Jan 6, 2012 10:34

grover: Jan 23, 2002; PEW PEW PEW

PPoison posted:

Please tell me about artificial neutral points... Let's say we have a wye-connected three-phase transformer with the neutral point connected to earth and a phase-to-phase voltage of 400VAC and 230VAC phase-to-neutral (a common configuration in Europe). Now let's get rid of the earth connection. If the loads are balanced we will still have 230VAC phase-to-neutral, the neutral now being called an artificial neutral point since it hasn't got a fixed reference point as the earth connection has been disconnected. Now, if the three-phase loads are unbalanced due to excess output on one phase, what effect will this have on the neutral point and the voltage on the other phases with respect to the neutral?

I've heard all the time that the voltage on a single phase with respect to the artificial neutral point will vary with the difference of loads, but I can't really understand why. According to KCL the current will be zero in the middle point of the wye regardless of the loads. What am I missing?

The neutral would be left to float, and could be any voltage. There is a magnetic component of transformers that is generally ignored, but serves to keep balanced 3-phased loads of floating delta (and wye) somewhat close to centered on ground. It's not enough to overcome a severe imbalance, though.

This is a dangerous condition, as it allows the individual line voltages to float higher with respect to ground than their insulation is rated for, and can cause ground faults. The advantage is that it would keep operating even if one phase shorted to ground- the grounded phase would essentially become the actual neutral, but no current would flow through the 1st ground fault unless there was a 2nd ground fault.

grover fucked around with this message at 16:17 on Jan 6, 2012

# ? Jan 6, 2012 16:14

PPoison: Nov 11, 2011

grover posted:

The neutral would be left to float, and could be any voltage. There is a magnetic component of transformers that is generally ignored, but serves to keep balanced 3-phased loads of floating delta (and wye) somewhat close to centered on ground. It's not enough to overcome a severe imbalance, though.

This is a dangerous condition, as it allows the individual line voltages to float higher with respect to ground than their insulation is rated for, and can cause ground faults. The advantage is that it would keep operating even if one phase shorted to ground- the grounded phase would essentially become the actual neutral, but no current would flow through the 1st ground fault unless there was a 2nd ground fault.

Why would it be left to float and why could it take any voltage? What's the theory behind it, the mathematics?

# ? Jan 6, 2012 18:46

SeaBass: Dec 30, 2003; NERRRRRRDS!

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.

# ? Jan 6, 2012 20:32

grover: Jan 23, 2002; PEW PEW PEW

PPoison posted:

Why would it be left to float and why could it take any voltage? What's the theory behind it, the mathematics?

Using 120/208 as an example, the mathematics are that you will always have 120V between the neutral and each of the 3 phases, and 208V between each of the phases, but there is nothing keeping the neutral at 0V with respect to ground. If the neutral floats up to +100V with respect to ground, all the other phases will be 100V higher, too, with respect to ground. The relative voltages between them will be unchanged, though.

# ? Jan 6, 2012 20:59

helno: Jun 19, 2003; hmm now were did I leave that plane

I cant tell you much about the math behind it but I can tell you that tearing apart a neutral bus on a 1 Gw generator is a pain the rear end.

Our predictive maintenance guys heard some signs of coronal discharge on a generator bushing. We had to take apart the nuetral bar so that AC hipot testing could be done on the individual phases.

The buss bar is two C shaped aluminum bars bolted onto the three bushings. Each half weighs about 100 lbs and is pretty awkward to move since it is made of three peices connected with welded on flexible links. All that is held on with 48 1/16" nuts that will only move with a 3/4 drive impact gun.

Turned out the bushing was fine and the corona was from a failign insulator on the IPB.

The Y point is grounded using a single 00 cable seems rather small considering how much current flows through that buss bar.

# ? Jan 7, 2012 04:40

Three-Phase: Aug 5, 2006; by zen death robot

What is the system voltage there helno? 24kV?

# ? Jan 7, 2012 05:25

helno: Jun 19, 2003; hmm now were did I leave that plane

24Kv normally puting out about 860 Mw.

# ? Jan 7, 2012 05:38

PPoison: Nov 11, 2011

grover posted:

Using 120/208 as an example, the mathematics are that you will always have 120V between the neutral and each of the 3 phases, and 208V between each of the phases, but there is nothing keeping the neutral at 0V with respect to ground. If the neutral floats up to +100V with respect to ground, all the other phases will be 100V higher, too, with respect to ground. The relative voltages between them will be unchanged, though.

I see! So the phase to neutral potential will not vary with changed loads. That sounds pretty obvious in fact, since otherwise the light would keep changing in brightness in hospitals and Norway and stuff that use the IT system.

I still don't understand the calculations behind why the neutral to ground potential changes though. Say you have a wye-configured 120/208 secondary with the phase current I1 = I2 = I3. The sum of the currents will be 0. But if you have asymmetrical loads, say I1 = I2 = x, I3 = 2x; the sum current till be greater than 0. But how does this affect the voltage with respect to ground? Why will the neutral point of the symmetrically loaded transformer "see" a potential equal to ground, when the only connection it has to ground is capacitive and (perhaps) negligable?

I do understand the risks (and the benefits) of not having a fixed reference point, but I really can't manage to grasp HOW the ungrounded neutral correlates to ground when they are not electrically connected (well, except cap).

Is it that you build up an electrical field not part of the electrical field of earth, so that the potential between these fields are more of a "random" thing than something you can predict? Having the electrical components grounded makes it easy to predict what may happen, but leaving the buildup of electric fields to nature makes it tough to deal with.

# ? Jan 7, 2012 08:15

grover: Jan 23, 2002; PEW PEW PEW

PPoison posted:

Is it that you build up an electrical field not part of the electrical field of earth, so that the potential between these fields are more of a "random" thing than something you can predict? Having the electrical components grounded makes it easy to predict what may happen, but leaving the buildup of electric fields to nature makes it tough to deal with.

Pretty much this. There are some magnetic components within transformers, and some natural capacitance between a line conductor and ground that have the effect of generally keeping the voltages close to centered around neutral under most conditions, while still maintaining a lot of the fault tolerance of an unearthed system. It was popular in hospitals because of this; a fault would not only not cause a fatal shock, but it would not trip the breaker, either!

Norway uses 230Y/400V 50Hz as the standard voltage; they used to use IT (unearthed neutral) as standard, but I believe they've since moved to TN (where the earthed neutral is the ground) and TT (US-style separate grounded neutral and ground conductors) for new construction. I suspect the advent of GFCI has a lot to do with the change.

US Warships use an ungrounded 120V delta for most circuits for similar reasons. To get 120V, two phase conductors are used (neither is a neutral.) Under normal conditions, each phase is only 69V to ground, which reduces the risk of shock, and there is fault tolerance because the equipment powered by it will keep working after a fault, too. All of which is important when mixing people and salt water and electricity, yet you can't tolerate breakers tripping during battle. (Some equipment even has "battle short" which bypasses fuses and circuit breakers in critical systems during battle, and eliminates the risk of nuisance trips, but at the tradeoff of repair costs, since the fuses no longer limit damage during equipment faults. Better to replace a few circuit boards than lose a ship and its crew, though!)

grover fucked around with this message at 14:26 on Jan 13, 2012

# ? Jan 7, 2012 16:00

DaveSauce: Feb 15, 2004; Oh, how awkward.

So I got a strange call from a customer the other day. They were installing a small VFD panel we built for them to control some HVAC equipment and the installing contractor was baffled at the incoming voltage. He says he's been doing this for years and he's never seen anything like it.

They claim to have dozens of 3ph 230VAC motors running in the plant, and the electrician swears up and down that it'll work fine. I can see that, but here's what he says is at the main power coming in to the building:

code:

        FUSE
L1 ----[|__|]----------
L2 --------------------
L3 ----[|__|]----------
        FUSE

My first thought was single phase off a center-tap transformer, but here are the voltages he measured:

L1-L2: 240 VAC
L1-L3: 240 VAC
L2-L3: 240 VAC

L1-GND: 240 VAC
L2-GND: 0
L3-GND: 240 VAC

Their story is that this building was the first to go up in the park, in around 1940 or so.

This appears to be a corner grounded delta system, something I've never had to deal with. I've only been doing controls for about 4 years, so I had to do a lot of googling to find that, but at least it explains why L2 isn't fused. I even showed it to our senior engineer and he was just as confused. Based on the voltages I'm sure it'll work, but is it safe?

The customer was worried that the VFD would freak out with this. I told him that in my opinion, as long as the ph-ph voltage is OK, then the VFD should be fine...but I also made sure to tell him that I couldn't make any promises (i.e. no warranty) since nobody at my company had ever seen this. Our senior engineer wanted to see a schematic from the power company before making any promises.

The rest of the story is that the power company told them that the building was overdue for a service upgrade, so I advised them to talk to them and get the upgrade if it's due to them. Might cost them more now, but it'd probably end up saving them in the long run. This was a week or two ago, so chances are they just wired it up anyway.

So what is the purpose of this setup, and how big of a problem is it for them to continue using it?

Thinking about it, if L2 is grounded, won't the VFD cause all sorts of noise in their power system? Or would it be the same as any modern setup?

edit: Another thought. If L2 is grounded, does that mean that I can't fuse/disconnect it in my panel? I'm using a standard 3ph fused disconnect, so they should all disconnect at the same time, but since it's fused there's no guarantee all 3 fuses would pop the same. I'm not sure how a single phase situation would affect L2.

DaveSauce fucked around with this message at 18:02 on Jan 7, 2012

# ? Jan 7, 2012 17:59

grover: Jan 23, 2002; PEW PEW PEW

I've only run into a few corner-grounded deltas, and it's always thrown the sparkies for a loop who've never seen it before. 3-phase equipment (motors, typical VFDs, etc) will see it as any other 240V delta and likely have no issues with it and run normally. You may have issues with surge protective devices, or if any of the electronics use ground as a reference.

The grounded phase doesn't need to be fused because it's grounded. And, yeah, VFDs are going to cause all sorts of noise, but not because L2 is grounded, just because they cause a lot of harmonics. Current flow through L2 will be the same as if it was a normal delta. Potential in L2 should always be 0 at the ground bond, so it shouldn't cause any noise in the rest of the system and more than you would get in the ground from any other the neutral bond.

I'm pretty sure you can fuse/disconnect L2 in your equipment, I don't believe there are any restrictions. Might be worth double-checking NEC, though.

grover fucked around with this message at 14:26 on Jan 13, 2012

# ? Jan 7, 2012 18:53

Three-Phase: Aug 5, 2006; by zen death robot

grover posted:

(Some equipment even has "battle short" which bypasses fuses and circuit breakers in critical systems during battle, and eliminates the risk of nuisance trips, but at the tradeoff of repair costs cost, since the fuses no longer limit damage during equipment faults. Better to replace a few circuit boards than lose a ship and its crew, though!)

Now that's a neat feature.

I believe that on fire protection equipment, you don't install circuit protective equipment. The idea is that if there's a fire, you don't want anything to interrupt critical pumps that are being used to fight the fire.

Also, on some motor protection relays like the GE Multilins, there is an emergency start feature. Big motors are usually limited to so many restarts per hour because this causes too much thermal stress/wear on the motor. If you short out the emergency restart terminals, the Multilin will "forget" the current thermal status and let you start the motor (serious problems like ground faults, failure to start/stall, phase loss, will still trip out the motor).

# ? Jan 11, 2012 00:14

helno: Jun 19, 2003; hmm now were did I leave that plane

Our Emergency backup oil pump is unfused. It is also a massively overrated DC motor that gets connected directly across a 250 VDC battery bank.

If that pump doesnt start when it is needed you have big trouble.

# ? Jan 11, 2012 00:16

Three-Phase: Aug 5, 2006; by zen death robot

One thing I remembered about 69/120:

I believe that on a lot of PT circuits, you typically get that ratio on the secondary. Like on an open-delta PT.

So 4160/2400 is stepped down to 120/69, except it's a delta so you really should never see the 69 volts.

# ? Jan 13, 2012 14:07

Cheesemaster200: Feb 11, 2004; Guard of the Citadel

I found the label making tool in SKM today....

I know its an old picture joke thing, but I always still get a chuckle out of it:

Only registered members can see post attachments!

# ? Jan 16, 2012 19:11

Criminally stylish: Dec 12, 2010; It's totally fine if you want to ride my disco-stick.

Im sorry if this question has come up and feel free just to quote the answer, and I would be a happy man

My uncle used to work alot with power and he was shocked pretty bad one day at work. Has this ever happened to you on some scale, or has it happened to any of your co-workers?

# ? Jan 16, 2012 19:25

Three-Phase: Aug 5, 2006; by zen death robot

I've got to print that label and show it to my co-workers. I have access to SKM Power Tools as well. Is that a real piece of equipment you did calculations on? I'm guessing that's the immediate secondary terminals before any protective systems or cables/busbars of a HV to MV transformer maybe 10MW or larger.

Actually, if you get burned badly enough, you won't feel any pain, but that's usually a really bad sign.

Criminally stylish posted:

My uncle used to work alot with power and he was shocked pretty bad one day at work. Has this ever happened to you on some scale, or has it happened to any of your co-workers?

I was hit with 70Vrms at a previous job across my fingers, a painful zing, and that was the highest. I was hit with more at home.

Where I work, it's getting harder and harder to do live work even at voltages as low as 120VAC. "Peeking" a live panel (removing or opening the access door from an energized 208/120 panel) is now effectively prohibited without a work permit and arc flash gear. Anything over 600VAC requires two LO/TO'ed breaks for safe work. Depending on the situation, opening and racking out a MV breaker may or may not count as two breaks. Everything is checked using a live-dead-live checking technique before anything is worked on. Buddy systems are used and there are safety guidelines that have to be followed at all times.

One of my co-workers was hit with 480VAC (not 277, it was line-to-line across his chest) at a previous job. He woke some time later up several feet from the panel with tremendous pain in his chest (broken ribs) and workers over top of him - frantically giving him CPR (hence the broken ribs) since his heart stopped. I think he was clinically dead for about a minute. Fortunately there weren't any lasting problems besides almost dying.

A good colleague for another company suffered a massive heart attack at place where he was doing field work. That wasn't electrical, however. Fortunately everyone he was around (electrical folks) were trained in CPR, and had an AED on him in less than a minute.

Fortunately, the facility I work at has a very stringent safety culture, one of the best I've come across. They definitely foster a "if you don't think what you're doing is safe, put your tools down and tell someone immediately, kick it up the chain of command if necessary." Lots of people are also CPR/AED trained and understand the electrical hazards present at a large industrial facility. (The high-voltage workmen especially are masters at their craft, but everyone who works on electrical systems is very competent.) We have had a few close shaves, but fortunately I don't think we've ever had an electrical fatality where I work. We intend to keep it that way if at all possible.

The biggest thing that scares me is miscommunication: like someone having an order to isolate breaker B012 but they isolate B021, and people open up a panel assuming everything is dead (when it really isn't). That's what double-checking for voltage is for, as well as multiple isolation sources, and making sure that when you build a system, you always put isolation means (like clearly labeled disconnect switches, both low and high voltage) near the loads that may be worked on.

Three-Phase fucked around with this message at 21:23 on Jan 16, 2012

# ? Jan 16, 2012 21:12

Cheesemaster200: Feb 11, 2004; Guard of the Citadel

quote:

I've got to print that label and show it to my co-workers. I have access to SKM Power Tools as well. Is that a real piece of equipment you did calculations on? I'm guessing that's the immediate secondary terminals before any protective systems or cables/busbars of a HV to MV transformer maybe 10MW or larger.

Actually, if you get burned badly enough, you won't feel any pain, but that's usually a really bad sign.

Close. Its actually two networked 5000 KVA transformers in an outdoor 33kV/4160V substation. I only show the utility above it with around 10,000 MVA of fault duty (to simulate an infinite source), which is why SKM freaks out. According to the arc flash report, the bus has 140kA of bolted fault current.... at 4160V. The arc-flash boundary is somewhere around 75 feet, haha.

# ? Jan 16, 2012 21:43

Three-Phase: Aug 5, 2006; by zen death robot

Cheesemaster200 posted:

Close. Its actually two networked 5000 KVA transformers in an outdoor 33kV/4160V substation. I only show the utility above it with around 10,000 MVA of fault duty (to simulate an infinite source), which is why SKM freaks out. According to the arc flash report, the bus has 140kA of bolted fault current.... at 4160V. The arc-flash boundary is somewhere around 75 feet, haha.

Transformer secondaries scare me. Truly, legitimately, scare me. Do you have a vacuum or SF6 breaker on the secondary that's rated for 1GVA of interruption or have some kind of fault limiters installed?

One thing I heard about awhile back (and I am very green with arc flash calculations, so correct me if I'm wrong) is that sometimes if your source has a higher fault capability, it can result to lower arc flash levels and vice versa. The idea being that a much more serious fault with tremendous amounts of current will trigger the instantaneous trip on the breakers in the path of the fault, where a source that limits the fault current will (obviously) have a smaller amount of fault current, but that would move up the trip curve on protective devices, so you may have a smaller amount of current, but be exposed to more cycles.

I need to check, but where I work I think with our connections we could easily have >1GVA of fault.

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...)

Three-Phase fucked around with this message at 23:37 on Jan 16, 2012

# ? Jan 16, 2012 23:28

SeaBass: Dec 30, 2003; NERRRRRRDS!

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.

# ? Jan 17, 2012 00:40

grover: Jan 23, 2002; PEW PEW PEW

What's a typical interruption time on a utility distribution fuse if there is a fault between a transformer secondary and the secondary OCP?

# ? Jan 17, 2012 01:46

Frozen Horse: Aug 6, 2007; Just a humble wandering street philosopher.

Cheesemaster200 posted:

I found the label making tool in SKM today....

I know its an old picture joke thing, but I always still get a chuckle out of it:

That's up there with the "Do not stare into beam with remaining eye." laser warning sign I saw outside one of the labs when I was an undergrad. On the other hand, if it can set your shirt on fire, you probably don't want to have your cornea focusing it on your retina.

# ? Jan 17, 2012 08:07

Cheesemaster200: Feb 11, 2004; Guard of the Citadel

quote:

One thing I heard about awhile back (and I am very green with arc flash calculations, so correct me if I'm wrong) is that sometimes if your source has a higher fault capability, it can result to lower arc flash levels and vice versa. The idea being that a much more serious fault with tremendous amounts of current will trigger the instantaneous trip on the breakers in the path of the fault, where a source that limits the fault current will (obviously) have a smaller amount of fault current, but that would move up the trip curve on protective devices, so you may have a smaller amount of current, but be exposed to more cycles.

That is correct. The less fault current you have, the slower the circuit breaker trips and the more incident energy you have. This becomes a bit of a problem once you get down to smaller voltages (e.g. 208Y/277V) when you can have fault levels under 1 kA.

# ? Jan 17, 2012 15:36

Three-Phase: Aug 5, 2006; by zen death robot

Frozen Horse posted:

That's up there with the "Do not stare into beam with remaining eye." laser warning sign I saw outside one of the labs when I was an undergrad. On the other hand, if it can set your shirt on fire, you probably don't want to have your cornea focusing it on your retina.

Not only can it set your shirt on fire, it can probably do it from more than ten feet away.

# ? Jan 18, 2012 00:35

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# ? Apr 16, 2024 07:02

McJuicy: May 9, 2008

Hey, I'm an apprentice electrician from Ontario. In a single phase system like a house you put a ground plate in. But does that really do anything? In case of a fault wouldn't it go through the grounded neutral at the street transformer? And would it even go there? Wouldnt it eventually get back to wherever the original neutral is at the power station? And how is that grounded conductor created? Is a large electrode stuck deep in the ground and that is considered the ultimate zero volts for an entire city?

On that subject, when you have an ungrounded camping generator, what happens in the case of fault situation? How is the metal of the generator bonded?

# ? Jan 18, 2012 01:42

The Something Awful Forums > Discussion > Ask/Tell > Ask me about industrial electricity 2: electric boogaloo

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