Re: ??Where to get a POLE Transformer??

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 4/7/01 2:44:10 AM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes: 



>
> Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-uswest-dot-net> 
> " <mystuffs-at-orwell-dot-net> 
>
> shad, all 
> a little while ago i had to find a 750 kva pad mount for our company, i 
> ran across alfa transformers site which is richly informative. 
> especially :http://www.alfatransformer-dot-com/coppervsalum.htm 
> i think most will be surprised that for our needs in coiling, aluminum 
> wound transformers are actually better suited. 
> i know i was. 
> well worth the reading. 
> marc 



Hi Marc & All 
(comments interspersed with text from above-referenced URL) 



"As with most questions of this type pertaining to transformers, a lot 
depends upon the application and the individual preferences of the person 
specifying the transformer. Quite often the reason cited for specifying 
copper windings is copper's high electrical conductivity. Although copper is 
better conductivity-wise than aluminum, copper is more expensive than 
aluminum and raw copper prices tend to widely fluctuate making cost 
forecasting difficult." 

Stability of MANUFACTURING COSTS is the key here. 

"During World War II, copper became scarce and was used primarily for the war 
effort. Several industries turned to aluminum as an alternative to copper 
because it was in good supply, was very stable price-wise and was less 
expensive than copper." 

Costs of manufacture still the key here. Why do you suppose aluminum was not 
specified for military applications if it's lighter, cheaper, and really 
almost as good? 

"In the 1940's high-power transmission power lines were converted from 
copper to aluminum and secondary power distribution networks began utilizing 
aluminum in the 1950's. Today, virtually all standard transformer lines from 
the major manufacturers are wound with aluminum." 

Lighter and cheaper again the keys. 

"Although copper wound transformers tend to be smaller than comparable 
aluminum wound transformers, aluminum transformers offer some distinct 
advantages over copper wound units: 

Both copper and aluminum oxidize over time. Aluminum conductors oxidize until 
all exposed aluminum surfaces are covered with an oxide layer. At that point 
oxidation stops unless the aluminum oxide barrier is somehow broken and the 
aluminum conductor is re-exposed to the air. Aluminum oxide inhibits chemical 
reaction of the metal with the wire insulation. Aluminum oxide is also a good 
electrical insulator." 

Actually Al2O3 is more of a very high resistance semiconductor.--> high R 
lots of heat. 

"Copper on the other hand oxidizes completely over time. Copper also acts as 
a mild catalyst, hastening the decay of the wire insulation. All of these 
factors combine to give aluminum wound transformers a longer life than 
comparable copper wound units, typically about five years." 

55 vs 50 years? 

"The heat storage capacity of aluminum is approximately 2.33 times that of 
copper (specific heat of aluminum is 0.214 cal/gram/°C, specific heat of 
copper is 0.092 cal/gram/°C). " 

With aluminum weighing much less than copper, the value of cal/gram/°C is 
dubious. cal/mil-ft/°C might be a better comparison. 

With aluminum wound transformers having a superior thermal storage capacity 
than copper wound units, they can withstand more surge and overload currents 
than copper units (normally exhibited when a motor starts.) 

This is the first possible plus. 

Although the conductivity of copper is better than that of aluminum, on a 
per pound basis aluminum is over twice as good a conductor as copper. 

This is the old peanut butter ad ploy: "Ounce for ounce, Skippy has more 
protein than steak". 

(I'd sooner have a whole 10 oz steak than a whole 10 oz jar of peanut butter 
for dinner). 

"Aluminum wire has received a negative connotation over the years primarily 
because of the care that must be taken in making connections. Copper 
proponents are quick to refer to hotel and mobile home fires that occurred 
where aluminum wire was present. Upon close examination it was found that the 
root causes of these problems is related to incorrect wiring devices being 
used." 

If you use standard (inexpensive, simple) devices, you get a fire. 

"Copper and aluminum expand at different rates when heated. If aluminum wire 
is used with wiring devices solely rated for use with copper wire, the 
connection heats up causing the resistance of the connection to increase and 
the temperature to continue to escalate." 

Different thermal coefficients means non-soldered connections loosen up over 
time and oxidation and arcing sets in. Since they claim Al transformers have 
the special transition connectors already in place, this one problem may be 
overcome inside the transformer.  (I still wouldn't use Al wiring. 

"Most transformer manufacturers address this problem by making a transition 
between the aluminum windings, either to a copper lead wire (or bus bar) or 
by terminating to an AL/CU lug (or connector). So why are copper wound 
transformers still specified? Again, we have to look at the application. 
Copper wound units may be specified because of space limitations. Copper 
wound units could also be specified due to the environment the transformer 
would be exposed to. If the environment would be corrosive to aluminum, 
copper wound transformers would make sense." 

O3 loves aluminum!! 

"Of course some people may just like copper wound transformers better for 
their own reasons." 

IMO, the "Aluminum is crap" attitude really applies to wiring more than to 
the already-built and buttoned up transformer, unless size is a problem. Just 
make sure you never replace any of the transformer's connectors with standard 
(copper) ones. 

Matt D.