Xfmr copper or Al

[cornbread]

I have some old 1000Kva xfmers (approx 40 years) and we are looking at rewind. The question came up if the original winding were copper? I said yes..due to the age....but really not sure how one can tell??? I saw nothing on the nameplate? ANy help would be greatly appreciated?:?

 

[JoeStillman]

I never heard of rewinding transformers. Is this common? It hardly seems economical.

 

[gar]

130513-1720 EDT

cornbread:

You certainly want to use the same wire as the original, but you can have better insulation today. You could not substitute aluminum for copper without derating the transformer. If the transformers are bad, then try to get at the winding wire and scrape the insulation to access the wire material.


JoeStillman:

There is a lot of value in the core material and scrap copper. Thus, makes sense to rewind. There are possibly better core materials today and this has to be considered. Transformer efficiency is also a consideration, and that relates to core material.

.

 

[mike_kilroy]

130513-1720 EDT
There is a lot of value in the core material and scrap copper. Thus, makes sense to rewind. There are possibly better core materials today and this has to be considered. Transformer efficiency is also a consideration, and that relates to core material.
.

Totall agree. although we used M3 thru m6 grain oriented silicon steel on all our transformers 40 years ago, lots of other folks did not. So if your core is cheaper higher loss steel, you need someone in the know to determine if it is worth rewinding or changing out core to lower loss material. I would suggest you send RFQ to 3 or 4 manufactures who also rebuild older units to get consensus then pick one you feel is best for your case. Also consider trying to find the OEM of that transformer and ask THEM what efficiency was, if Al or Cu, what type core steel was used, and if THEY rebuild. Often you can get a clue by studying the core laminations: how many did they stack in SAME direction at one time? If 1-3 or so, it was pretty high quality build and probably used a high grain oriented steel; if you see more then they went more for save time and build it cheaper and thus higher losses....

 

[Sahib]

It all boils down to this:

To repair or replace is a matter of money.

 

[Sahib]

I have some old 1000Kva xfmers (approx 40 years) and we are looking at rewind. The question came up if the original winding were copper? I said yes..due to the age....but really not sure how one can tell??? I saw nothing on the nameplate? ANy help would be greatly appreciated?:?

Try to contact the transformer manufacturer or search the old records for the specifications of the transformer.

 

[iwire]

Unless it is non-standard in some way I have no doubt scrapping the old and buying new would be the most cost effective way.

 

[templdl]

Unless it is non-standard in some way I have no doubt scrapping the old and buying new would be the most cost effective way.

Mega dittos. I had been in the electrical industry for 21 years working as a sales and application engineer for a dry type transformer for 3 years. The Op has no idea of the cost to disassemble the core in order to even remove the coils. The most would be prohibited as well is the design being obsolete. In addition, AL wound transformer is designed different than a CU wound.

 

[gar]

130514-2205 EDT

The real question is economic. Thus, one needs to get actual data. A consideration that may be overlooked is taxes. If you rebuild an old transformer, then it is probably written off as an expense. A large new transformer probably has to be capitalized. This can be a big cost. So if it costs more to rebuild than to buy new it still might be less expensive by expensing a repair.

I have seen whole machines that were totally rebuilt, having only salvaged the machine base, with the essentially new machine being written off as a repair. Very big dollar difference.

.

 

[Besoeker]

I never heard of rewinding transformers. Is this common? It hardly seems economical.

Might depend on the rating.
I'm sending a couple of guys to pull out a 3,300V/660V 100kVA unit to get it inspected/repaired/rewound following the insulation failure of a winding temperature switch.

 

[Sahib]

I have some old 1000Kva xfmers (approx 40 years) and we are looking at rewind. The question came up if the original winding were copper? I said yes..due to the age....but really not sure how one can tell??? I saw nothing on the nameplate? ANy help would be greatly appreciated?:?

Temperature coefficients of copper and aluminium can be different. So for copper transformer conductor of 100% conductivity, its temperature co-efficient 'α' at an initial temperature 't1' may be found in reference books. Let 'R1' be the measured resistance at that temperature. If 'R2' is the measured resistance at a higher temperature 't2', then these values should satisfy the equation:

R2=R1*(1+α*(t2-t1))..............(1)

If (1) is not satisfied, the transformer conductor is aluminium.

 

[petersonra]

I have heard it is sometimes done on larger transformers.

I can't imagine it is practical on more normal sized stuff. The other issue is that older transformers probably won't comply with modern standards and just rewinding it won't change anything but the insulation. It won't be anymore efficient or able to deal with harmonics any better.

 

[jim dungar]

The question came up if the original winding were copper? I said yes..due to the age....

Age has nothing to do with whether the windings are AL or CU. Even 40years ago AL was very popular.

The easiest way to tell the difference is where the windings are connected to the bussing. The material in an AL 'weld' joint looks the same as the bus bars while a CU connection may look like it is made of different material. Of course if you are scrapping the transformers, you could cut open the winding leads.

Is this a dry type transformer or a liquid cooled one? It seems to me that dry type are not rewound any near as much as liquid ones are.

 

[robbietan]

I have heard it is sometimes done on larger transformers.

I can't imagine it is practical on more normal sized stuff. The other issue is that older transformers probably won't comply with modern standards and just rewinding it won't change anything but the insulation. It won't be anymore efficient or able to deal with harmonics any better.

agree here. specially on transformers with unusual specs ( 2 MVA, 34.5kV/400V).

if the transformer is one MVA, there are usually a lot of the stuff in someone's storage area