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#119389 12/24/04 04:06 PM
Joined: Jan 2003
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iwire Offline OP
Moderator
If you read this post
https://www.electrical-contractor.net/ubb/Forum1/HTML/005239.html

you know the company I work for has a large super market chain for a customer.

Here is another of their locations that had an outage.

I was not involved with this one, I don't know where I was while this was being repaired.

[Linked Image]

[Linked Image]

[Linked Image]

[Linked Image]

[Linked Image]

[Linked Image]

I am told the high voltage cut out did not open until the oil in the transformer was boiling and the primary's shorted.

Some of the guys on this repair got to see a security tape of the sparks blasting out of the pipe until the power failed.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Jun 2004
Posts: 206
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Member
What a long day that repair turned out to be. The temp generator was installed on Sunday. On Monday we started at 6:00 am and left for home at midnight with the store back on normal power.
The security tape iwire talks about was incredible. The sparks shot 75 feet from the conduits out to the street. The tape lasted 1 1/2 minutes before the power went out.

Joined: Oct 2004
Posts: 806
Member
Wow!! Incredible pics!! I sure wouldn't have wanted to be in those houses across the street! (On the other hand, it would've made for an exciting light show.) [Linked Image]

Luckily that padmount shorted and took the HV fuses before it exploded too. What a mess that would have been on top of this.

Any info on what caused the initial fault?

And any chance that video can be encoded and put online? Might make for a good safety discussion.


Stupid should be painful.
Joined: Dec 2000
Posts: 4,294
Member
Wow!
That burnt up like it was tinfoil. [Linked Image]
Must have been spectacular.

Joined: Oct 2003
Posts: 289
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Member
What caused the short circuit on these wires in the conduit/box?

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iwire Offline OP
Moderator
We do not know the cause here, once our guys get there the cause is unimportant, they just start ripping the old out and replacing it.

The utility had to change the pad mount and our guys had to replace the conduit and conductors.

The conductors go a bit inside as well the electric room is the penthouse you can see in the photos, the conduits go in to the bottom of the gear in the penthouse.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Feb 2002
Posts: 840
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Quote
I am told the high voltage cut out did not open until the oil in the transformer was boiling and the primary's shorted.

Bob, I take it these are service conductors?

This looks like a perfect illustration of the reason that <1000 amp WYE services require GFPE!


Peter
Joined: Jan 2003
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iwire Offline OP
Moderator
Yes these where service conductors and yes once inside they hit a 1,600 amp main with GFP protection.

I think it is a good illustration of why the service disconnect is required to be located "nearest the point of entrance"

In this case there is I would guess 10' to 15' of service conductors inside before they reach the service disconnect.

It is a good thing the fault did not happen on the inside portion.

This service is 480Y/277 1,600 amp fed with 4 sets of 600 kcmil CU in 4" RMC.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Oct 2004
Posts: 806
Member
Quote
This looks like a perfect illustration of the reason that <1000 amp WYE services require GFPE!

In this case, wouldn't the GFPE be located in the building's switchgear? Since these appear to be the service conductors the GFPE wouldn't help. [Linked Image] [Edit: Iwire's post went in as I was typing this [Linked Image]]

Something on the idea of a cable limiter that utilities use would do the trick. It would have been located at or in the padmount.

Originally I was going to remark that better fuse coordination by the utility would have limited the damage, but it's possible that depending on the primary connection the fault current seen by the primary wasn't high enough to open the fuses at the start of this fault. (Thinking delta/Wye).....
Quote
We do not know the cause here, once our guys get there the cause is unimportant, they just start ripping the old out and replacing it.
Please do not take this the wrong way, I mean no offence here, [Linked Image] but if something like this happened to any installation or repair I was involved with, I would certainly want to know what caused it! [Linked Image]

[This message has been edited by mxslick (edited 12-25-2004).]

[This message has been edited by mxslick (edited 12-25-2004).]


Stupid should be painful.
Joined: Jan 2003
Posts: 4,391
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iwire Offline OP
Moderator
No offense taken. [Linked Image]

The customer does not care what happened at first, they average about $1,000,000 per week gross at each location. That is a little under $150,000 per day. What they do care about is the power is restored immediately.

Once they are back on line then they want to know what happened, then any clues are in the dumpster or scrap yard.

Yes the generator we bring in allows them to open for business. The generator burns 75 to 100 gallons per hour or about $3,600 per day plus rental costs.

In a case as bad as this it really does not matter what happened all the damaged equipment is replaced.

As far as power company fuse coordination it is not possible to fuse the primary side of the transformer in a way that will protect one set of parallel conductors.

Individual cable limiters would be an option I guess, but I have never seen that done.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Feb 2002
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Quote
Since these appear to be the service conductors the GFPE wouldn't help.

Sorry that I wasn't clear. What I mean is, imagine this fault occuring on the load side of the disconnect, without GFPE. [Linked Image]


Peter
Joined: Nov 2000
Posts: 2,148
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Member
At a fire a few years ago, I watched as 30' of 4" rigid and 3 500kcmil cables vaporized. This was on a 120/240 volt single phase servive. There was much less of the conduit left than what is shown in Bob's pictures. It was a great fireworks show for about 25 minutes. The 750 kva transformer in an underground vault got hot and the cables at the transformer were smoking, but the primary fuses never opened and the transformer was not damaged.
Don


Don(resqcapt19)
Joined: Oct 2004
Posts: 806
Member
Bob:

Thanks for the info. With those grosses, I'd feel the same way! And I'm sure the genny costs seem like nothing against the potential losses. [Linked Image]

Interesting that it is true the idea of investigating the cause has to take a back seat to restoration [not trying to be smarta**]of service. I have always had a facination and curiousity of all things electrical and if I had the necessary background would like to start an "investigation" service to pinpoint causes of incidents like this one. [Linked Image] I wonder if such a company exists?

And as for cable limiters, I wonder if they'd work on paralled conductors?

CTwireman: Excellent point. Now who would want to be the one to open the service disconnect with this kind of fault happening? [Linked Image] 480y/277 @ 1,600 amp rated...As a rough stab I'd guesstimate the fault current to be in excess of 50,000 amps that close to the transformer!

Happy Holidays gentlemen!!

Tony


Stupid should be painful.
Joined: Nov 2000
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Tony,
Quote
And as for cable limiters, I wonder if they'd work on paralled conductors?
I've never installed cable limiters, but I thought that their main use was on both ends of all of the parallel conductors.
Don


Don(resqcapt19)
Joined: May 2003
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e57 Offline
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WOW! Bob how much of that is going to be saved? I imagine that the buss work in the gear those conductors were parraleled to may have got pretty hot too. As to the cause, I would be checking EVERYTHING before it went back on line.

I'd love to see that security video....


Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Apr 2004
Posts: 201
Member
Don, cable limiters are required to be installed on three or more sets of service conductors on our downtown network . We install them on our end of the service lateral and the electrical contractor is required to install them on the load end of the service lateral. The interesting thing is that we do require them to be installed where the service is off the downtown network. The situation that Bob has would not have been protected by cable limiters unless the customer wanted them.

The reason we require cable limiters on our downtown network is the loss of a building where one set of several parallel sets of conductors faulted. The current from the remaining parallel sets fed the fault by going through the service bus and back to the fault. This burnt up the service equipment and the building as well. We got to pay for part of the building since we didn’t do anything to prevent this situation from happening. I suspect we will start requiring cable limiters on outlying services as soon as we have to buy a portion of one. [Linked Image]

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Charlie Eldridge, Indianapolis, Utility Power Guy


Charlie Eldridge, Indianapolis Utility Power Guy
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http://www.bussmann.com/library/bifs/1042.pdf

Question--
Why is 3 conductors per phase the magic number?

Joined: Apr 2004
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Redsy, you ask a good question and I would like to know the answer also. I know that we have the same requirement. [Linked Image]

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Charlie Eldridge, Indianapolis, Utility Power Guy


Charlie Eldridge, Indianapolis Utility Power Guy
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How does the customer know if a cable has faulted, and the cable limiters for it have opened? If there are say 2 other cables that are still in service supplying the load. Everything would look to be normal, but for one phase only has 2 functioning cables vs 3 functioning cables for the other two phases. You may have eddy currents if there are three conduits, each with 3 phase cables, and one of the conduits has a dead phase. How would the customer know that there is a problem that needs to be fixed? If he chooses to ignore it, well that's another issue....

Joined: Apr 2004
Posts: 201
Member
We have a team that checks for blown cable limiters on our network to see if we have had any fail. We have not had any service laterals fail because of lost cable limiters. [Linked Image]


Charlie Eldridge, Indianapolis Utility Power Guy
Joined: Jul 2002
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Wow!,
This looks like a big job.
Just a silly little question, were the wires in the 3 conduits above the one that blew out, checked or tested to make sure that they weren't damaged from the heat?. [Linked Image]

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iwire Offline OP
Moderator
Hi Mike

Quote
were the wires in the 3 conduits above the one that blew out, checked or tested to make sure that they weren't damaged from the heat?.


All wires replaced. [Linked Image]

The switchgear was checked by a manufacturers (GE) technician.

Bob

[This message has been edited by iwire (edited 12-27-2004).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Jun 2004
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Mike, not a silly question at all. As Bob said all cables were replaced. Yes it was a big job. We started out with five guys at 6AM. Brought in 2 more at 10AM, and 3 more at 4PM. We all left at midnight with everything packed up. Except for the painters coming the next day you would never have known we were there.

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I'll take a stab at the cause: Insulation damage on the conductors in the bottom conduit where they emerge through the bushing.

It looks like the bonding-bushing lugss on the other three conduits could be pressed into their respective conductors, too.

I try to "pre-bend" wires to keep them centered in, or at least not jammed against, the conduits from which they emerge.


Larry Fine
Fine Electric Co.
fineelectricco.com
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e57 Offline
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I say it was the bullet hole in the conduit in picture #3. What ever blew it was vaporized early in sceme of things.


Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Oct 2004
Posts: 806
Member
Bump... [Linked Image]


Stupid should be painful.
Joined: Jan 2006
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Now THAT is a real eye opener to what can happen !!!That would have been something pretty spectacular to see... That would put some fireworks displays to shame!

Some years ago when I used to work at the supplier a building down the road had its main underground service short out and it also wiped out the padmount transformer ( Service was 400A 120/240V 1 phase, that consisted of 2 ducts containing 3/0 TWH in paralell)... One of the ducts shorted and burned the conductors bare from the transformer to the fault... Turns out when they were pulling out the damaged conductors, a chunk of broken fish tape was drawn out right where the fault appeared to have originated, and had been tangled in there since day one.. About 15 years if not a bit longer..

A.D

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New Member
Bob, Could I have your permission to use your photo. Of course I would give credit.

Joined: Apr 2002
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DHester:
Welcome to ECN forums!

Iwire (Bob) has not been active on this forum for some time.

You may want to try sending him an email.



John
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