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| Transformers |
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-> High-Efficiency Utility Transformers
Mean Lowest Total Owning Costs
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| High-Efficiency Utility Transformers Mean Lowest
Total Owning Costs |
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  Almost
all electric utility transformer purchases are "loss evaluated"
units.
This purchasing practice has increased significantly in the
past 15 years as utilities have become aware of the range of
losses at each kVA rating in units currently available and the
value of these losses. On the other hand, very few non-utility
buyers conduct loss evaluations. Many purchase transformers
on a first-cost basis only.
Consideration of transformer efficiency is critical to reducing
the load impact on the power producer and to the total owning
cost of the purchaser.
Transformer efficiency is influenced by many factors. Primary
influences include the choice and quantity of the conductor
used in the windings in addition to the quality of the core
material. The better the conductor, the lower the heat or I2R
losses.
Copper is a more efficient conductor than aluminum; an enlarged
cross-sectional area of copper results in lower resistance and,
therefore, lower I2R losses. Many transformer units have actual
conductor watt losses that are three to four times core watt
losses. Such conductor losses can range from a low of near 130
watts to 350 watts or more for a 25 kVA unit. Levels ranging
above 200 watts are unnecessary and may be costly. Purchasers
should be encouraged to examine the actual load and duty cycle
of each transformer and the resulting I2R conductor loss and
its impact on their cost of operation before making a purchase.
Loss evaluation can be a complex process. However, as utility
companies have learned, this evaluation is an important step
in the purchasing process and one that commercial and industrial
users could benefit from greatly.
Higher "loss evaluation" values result in more expensive transformer
units. However, use of better transformers leads to lower actual
watt losses and reduced operating costs. Therefore, life cycle
cost evaluations should be expanded to cover all transformer
units above about 10 kVA rather than simply comparing "first
cost" among units available, as is currently done with many
distribution transformers- pole-mounted, pad-mounted or dry-type.
Transformer life for utility units is expected to be 30 to 40
years. Therefore purchasing practices based on loss evaluations
and life cycle costs can yield significant savings.
For utility-type transformers, there has been a long-term trend
toward designing transformers for increased efficiency of operation
(lower losses), based on the increasing costs of wasted energy
in the utility grid. This trend has resulted in the use of more
metal in a given transformer, and a trend toward more copper
since it is inherently more energy efficient. |
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