proper way to decomission a 34.5kV to 4160V transformer

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mshields

mshields

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Boston, MA
Other than PCB concerns, is there a standard which defines the safe decommissioning of a transformer. I'm wondering how the core is demagnetized. Correct me if I'm wrong but I believe that you can still be killed by the capacitance built up in the unit after you've disconnected it from it's source. True?

Thanks,

Mike
 
mshields said:
Other than PCB concerns, is there a standard which defines the safe decommissioning of a transformer. I'm wondering how the core is demagnetized. Correct me if I'm wrong but I believe that you can still be killed by the capacitance built up in the unit after you've disconnected it from it's source. True?

Thanks,

Mike
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Capacitance and inductance (related to magnetization) are two very different things.

A Power Factor Correction capacitor bank can be very dangerous if not properly discharged.
A transformer might have some incidental capacitance between the primary winding and the case or secondary windings, but I doubt that the charge would persist very long.
As far as residual magnetization in the core, it would only be a concern in terms of the mechanical forces when disassembling it or attracting fasteners and tools as you get close to it. Since the field is designed to be contained within the core, the latter should only be an issue during disassembly of the core itself.
(You could always just heat it above its Curie temperature and all of the residual magnetism would go away.) :)

PS: Even if the transformer oil does not contain PCBs, there may be regulated concentrations of heavy metals in it after extended use.
 
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With any piece of equipment that's being de-energized, I have always just seen the crew put on PPE and then drain it to ground.

Out of curiosity, is there something further you would do for a large capacitor?
 
If you have questions regarding this my advise would be to hire someone who has this experience. This is not something that a amature shold be doing. If this is something that you intend on doing in the future this may be your opportunity to work beside someone who has expertise in this proceedure. unless the 34.5kV has been disconnected entirely and the transformer isolated and properly grounded I wouldn't mess with it. It must be realized that a transformer will be also dangerous when backfeed from a load side source. It is imparative that the transformer be completely inert.
Also, what is your definition of decommissioning include?
 
mshields said:
Other than PCB concerns, is there a standard which defines the safe decommissioning of a transformer. I'm wondering how the core is demagnetized. Correct me if I'm wrong but I believe that you can still be killed by the capacitance built up in the unit after you've disconnected it from it's source. True?

Thanks,

Mike
Click to expand...

apply personal shorts and grounds, and leave them there, with a tag on them.

after the unit is removed from the installation, you could take a #6 bare wire,
and tie all the primaries, secondaries to the case, then remove your personal
shorts and grounds, and leave it that way.
 
GoldDigger said:
I think it means something like scrapping it based on the other language of the OP's post.
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"I think it means" is making an assumption based upon very little if any information about what is meant by decommissioning and you haven't a clue as to how big this transformer is. How about providing the nameplate information and the date of manufacture. Is it know of it is a dry the or liquid? Trying to answer a question when little if anything at all is know about the transformer I find to be interesting.
Power center, unit sub, substation, pad mount, 500kva, 5000kva???
 
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templdl said:
"I think it means" is making an assumption based upon very little if any information about what is meant by decommissioning and you haven't a clue as to how big this transformer is. How about providing the nameplate information and the date of manufacture. Is it know of it is a dry the or liquid? Trying to answer a question when little if anything at all is know about the transformer I find to be interesting.
Power center, unit sub, substation, pad mount, 500kva, 5000kva???
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his main concern seemed to be safety.
as far as decommissioning for scrap or long term storage, it's a different deal obviously.
long term storage, the main concern is moisture in the core, and oil contamination.

but every transformer i've ever seen sitting there disconnected, has all the primaries
and secondaries tied together with a #6 solid copper wire, tied to the can. POCO rules
around here, if it's not shorted and grounded, it's presumed to be energized, and that
also applies to any equipment just sitting there unconnected.
 
Fulthrotl said:
his main concern seemed to be safety.
as far as decommissioning for scrap or long term storage, it's a different deal obviously.
long term storage, the main concern is moisture in the core, and oil contamination.

but every transformer i've ever seen sitting there disconnected, has all the primaries
and secondaries tied together with a #6 solid copper wire, tied to the can. POCO rules
around here, if it's not shorted and grounded, it's presumed to be energized, and that
also applies to any equipment just sitting there unconnected.
Click to expand...

All this is assuming. All too much to,e is waisted on athis form when the OP is not specific in defining what his actual question is a illustrated by the string of posts.
Do you have any idea as to what transformer he is dealing with as I have pointed out in my previous post? Or what is ment by decommissioning?
 
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