Value Points - Copper vs. Aluminum Conductor
There is a common misconception that a distribution transformer
with copper windings is in some way more efficient, more
reliable, or has higher short-circuit strength when compared to a
transformer with aluminum windings.
Recommendation
Improvements in technology regarding the use of aluminum in
transformers have made aluminum-wound transformers the ideal
choice for today’s applications.
Rationale
Operating Cost
Cooper Power Systems designs aluminum-wound
transformers with windings of a larger cross-sectional area
than would be used for a copper wound unit. This larger
cross-sectional area translates to a lower current density and
an equivalent operating temperature. By reducing the current
density in the windings, a low-loss design can be achieved
with aluminum or copper windings.
Reliability
Because Cooper Power Systems aluminum-wound and
copper-wound units run at equivalent operating temperatures,
the insulation systems age at the same rate for each design.
Lower First Cost
Whether low losses are the goal or not, aluminum windings
are less expensive than copper windings. The following
example shows two equivalent loss designs, one with
aluminum windings and one with copper windings.
The Bottom Line
Cooper Power Systems designs its aluminum-wound coils
using the same thermal, dielectric and mechanical performance
requirements as for its copper-wound coils. In pad-mounted and
substation designs, Cooper Power Systems aluminum-wound
units and copper-wound units serve their loads equally well.
A transformer’s life is defined by the life of its insulation system.
Example: 2500 kVA, 3-phase padmount transformer, 13800 Delta - 480Y/277
No Load Losses (Watts)
Load Losses (Watts)
Total Losses (Watts)
Efficiency at 50% Load
Efficiency at 100% Load
Dimensions (H x W x D)
Price
All Aluminum Winding
All Copper Winding
2155
17,725
19,880
99.5%
99.2%
72″ x 66″ x 55″
$36,745.00
2272
17,225
19,497
99.5%
99.2%
64″ x 68″ x 52″
$42,565.82
Copper Primary
Aluminum Secondary
2144
17,544
19,688
99.5%
99.2%
64″ x 68″ x 58″
$39,843.27
In this example, while the losses of all three units are roughly equivalent, when compared to the price of the
aluminum-wound unit, the copper-aluminum-wound transformer is $3100 (8.5%) more expensive, while the
copper wound transformer is $5800 (16%) more expensive.
For an in-depth, technical explanation on this issue, please see reference document R210-80-3.
www.cooperpower.com
B210-99028 • April 2011 • Replaces 99028
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