Is Aluminum-Aluminum wound transformer better than Copper-Copper Transformer?

[flee_flap0508]

Copper-wound Transformers were proven tested to be reliable and were used by utilities years ago, because of its low-cost and capabilities. However, with their high cost nowadays, we plan to use Aluminum-wound transformers.
Based on facts, aluminum's characteristics in terms of its electrical and mechanical capabilities can equalize that of copper's, given some enhancements.. However in actual set-up in the field, is aluminum-wound transformers, especially wire connections, internal and external, reliable and safe from breakdown or damage due to mechanical, thermal and electrical stresses? Also, Do aluminum transformers have higher transformer and insulation life? I need your expertise and point of view on this matter. Thanks a lot!

 

[Phrak]

Aluminum is subject to failure by heat embrittlement.

 

[Mike_In_Plano]

Aluminum has been used for years as cast-in shorting bars in inductance motors. It's also been used successfully in high tension lines. It had a poor showing in house wiring because of poor contacts and resulting fires, but then again, some of the approved methods with copper are scary.

The world is grunting under the weight of copper prices. With over sized cores, I can see where aluminum is likely a good substitute for cost vs performance. If UL and EPRI both say it's safe, than that's good enough for me.

- Mike

 

[Bob S]

Because of the higher amps-per-cm² rating of copper in transformer coils, use of copper results in smaller transformers. So you will have to do a trade-off analysis of copper-wound vs. aluminum-wound transformers. If size is important, copper is better.

Bob S

 

[flee_flap0508]

So do you mean by all means, Aluminum Transformer is ineffective to be used?

 

[Mike_In_Plano]

By the old standards of transformer production, the goal was cost vs loss with a balance between copper loss and core loss. Then, the ribbon cores came out, and the transformers were redefined since core loss dropped way down. Then, it became a matter of dropping the overall cost by getting copper out. The core loss was still less than that of the copper.

Now, copper prices are crazy high, and ribbon core material is cheaper than ever. I can see where it makes good sense to up the core size, up the overall transformer size, get the same loss and save some money. As for weight, the core size would be pushed up to accommodate the need for a larger winding window, but aluminum weighs far less than copper. I'm curious as to whether it's a wash.

 

[mgb_phys]

If you have friends in high places silver is even better
http://www.physorg.com/news182628141.html

Copper is about 80% better conduction than Al but weighs more than 3x as much

 

[flee_flap0508]

Mike, thanks for the info..

Our utility is planning to purchase 3-phase pad-mounted transformers for upcoming enhancements.. Cost is a very much factor for this move.. With regards to the liabilities of aluminum with respect to power losses, and strength, there are enhancements made to make this same with that of copper's performance.. making big savings without compromising quality only the copper Xmer could provide.. Aluminum has high calorific capacity, 16.7% higher than that of copper, so technically, Aluminum can dissipate heat providing better thermal behavior and insulation protection during high rush current.

Our only concern is the effectivity of aluminum transformers. We have been using copper for a long time. This is the first time we are going to employ Aluminum due to its relatively low cost compared to copper. Our only guarantee for planning to use aluminum is the possibility of equalizing its performance that of copper at the same time, obtaining big savings.. What do you think about it? thanks a lot..

 

[Phrak]

I'd have thought that you would have some over-the-counter or in-house transformer modeling software that could answer most of the tradeoff questions.

 

[flee_flap0508]

Phrak, good morning.. where can I find that software? I was surfing all day long looking for some simulation software that can model the distribution transformer with all of the actual scenarios present in the field..

 

[Bob S]

Here are some numbers for comparison. 10 Ga copper wire has a resistance of 1.02 ohms per 1000 feet. !0 Ga aluminum wire (same diameter as copper) has a resistance of 1.64 ohms per 1000 feet. With regard to the core, I suspect that pad-mounted 3-phase transformers use silicon-iron sheet laminations, not a ribbon core.
Bob S

 

[Mike_In_Plano]

I've always done my design transformer and inductor work on mathcad, but a lot of guys follow the techniques outlined in Col McLyman's Inductor and Transformer design book and do it on paper or Excel.

I don't think you'll find anything useful through the analysis. Can you get the same efficiency with aluminum as you can with copper? Yes, definitely, but you'll need a larger core to accommodate the larger cross section of the aluminum.

Does this make a difference as far as the cost? Yes, aluminum is relatively cheap compared to copper, and the core material is likely cheaper than either.

If there's an issue, it would lie outside the scope of a simple analysis. For example, are the connections as reliable with aluminum as they are with copper? Or, is the structure associated with the windings as stable with aluminum?

I think in the end, it comes down to whether you trust your manufacturer to deliver a well constructed product. It's certainly not the well developed technology we've become accustomed to.

Likewise, there's the question of whether the contractor fully understands and is willing to properly rate and install the equipment.

 

[Bob S]

Are the windings in large power transformers hollow rectangular wire? I know that the windings in large particle accelerator magnets are hollow water-cooled rectangular copper wire (bus bar), and are designed to carry ~600 to 800 amps per cm². I once worked on a nuclear research reactor many years ago, which had an aluminum heat exchanger on the primary core coolant system. Someone didn't watch the pH in the secondary side, and within a few months, there were pinhole leaks in it, because the pH got up to about 8.0. Hollow water-cooled aluminum conductor should not be used.

Bob S

 

[Phrak]

Phrak, good morning.. where can I find that software? I was surfing all day long looking for some simulation software that can model the distribution transformer with all of the actual scenarios present in the field..

Good evening. The folks I deal with for 50/60 Hz application transformers seem to either have developed their own software or have purchased it. I've simply been happy to provide loading requirements rather than specifying core and wind specifications.

Westinghouse had most of this transformer geometry/winds optimization problem figured out about ~70 years ago, though consideration of the relatitive heat capacity and conductivity of iron vs. aluminum should be more recent.