losses in transformer - CU vs ALU

[tem1234]

Hi,

We need a 2.5 MVA transformer for a little generating power station. We need to choose between an ALU vs CU transformer. Of course the ALU TFO is less expensive.

I would like to know, is it true that an ALU TFO will have greater losses than a CU? If yes, how can we calculate in how much time the extra money for the CU TFO will be paid by saving on the losses?

There's not a lot of info, this is just for a premilanary report

Thanks

 

[tem1234]

I forgot to say, the TFO will be dry type.

 

[stevenal]

http://www.usda.gov/rus/electric/pubs/1724e301.pdf

 

[jghrist]

The transformer can be designed for low losses with either copper or aluminum windings. Evaluating losses using a method similar to the RUS document linked by stevenal will allow the manufacturers to design the optimum transformer for your loss costs.

You might want to specify copper on the high voltage winding for mechanical reasons. Small aluminum windings and leads can get fatigue failure from vibration. That's not so important on the low voltage because the conductor size is larger.

 

[tem1234]

thanks to both of you. I think i have to ask to the manufacturer what is the losses of their tfo.

Interresting point jghrist about the fatigue of small aluminium winding.

 

[dpc]

I'd just add that the losses difference are only in the load losses, not the core losses so any comparative evaluation will be sensitive to your assumptions of the actual transformer load. The load losses vary with the square of the current. So if you assume 50% load factor versus 90% load factor, there could be some big differences in the results.

Unrelated to losses, one disadvantage of aluminum windings that I've heard cited is core damage in the event of a winding failure. Supposedly aluminum windings will "spatter" more during internal winding faults, causing greater core and tank damage. The end result is that transformers with AL windings get totaled out after faults more often transformers with CU windings.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[trosepe]

I would look more for the lower temp rise rating than if it has copper or aluminum windings. 150 degC rise transformers have much higher load losses at the same load as does a 115 degC rise unit. The 115 degC rise unit has lower load losses, makes less noise and should last longer. Be sure to order with a good temperature sensor system and robust fan package.

 

[tem1234]

thank you, it's always a pleasure to learn more on this forum . I'll take a look at this.

 

[wolf39]

I'm surprised that a transformer with aluminum windings is cheaper than a transformer with copper windings. Do you have price numbers to share with us?

If you consider a loss evaluation, which can be several thousands of $ per kW, you would go for a conventional copper type. Apart from the higher winding losses, the aluminum windings also require more space, this resulting in bigger cores and higher iron losses.

Let the manufacturer quote for both types and with the loss evaluation you can decide. Better even, let the manufacturer have your loss evaluation figures and let him decide.

Regards

Wolf

http://WWW.HYDROPOWER-CONSULT.COM

 

[tem1234]

Hi Wolf,

I'm not sure about if it's a good idea to post the price on a forum, but i can say that the alu tfo is 23 % less expensive than the CU.

The transformers isn't from the same manufacturer, but i'd ask for losses. An interresting thing is that the CU TFO manufacturer offer 2 tfo, one which respect the standard CSA C802.2 (minimum efficiency value for dry type tfo) and one cheaper (but still more expensive than the ALU) which didn't. I'll ask him to tell me which is better with my load and the kwh price. Pretty sure that the first one is the best solution.

We don't have much info for the alu tfo, almost only the price!