TMS-811-1/AFJMAN
32-1080
ARRANGEMENT ONE
Recommended as expansion is easy
Transformer
Transformer
Feeders
Feeders
ARRANGEMENT TWO
Not recommended as expansion is difficult
US Army Corps of Engineers
Figure 4-3. Single-Line of Primary Unit Substation with Two Transformers
time divided by the operating time during the
age levels at either new or existing stations.
analysis period).
Step-voltage regulators may be required for
(6) Loss evaluation. To ensure that a power
switching stations and in substations that are not
transformer with specific losses is delivered by the
equipped with circuit study for a medium-voltage
manufacturer, a loss evaluation/economic evalua-
bus, only medium-voltage motors should be consid-
tion will be performed in accordance with guide-
ered. The short circuit current contribution from
lines in IEEE C57.120. When the evaluation indi-
low-voltage motors dies out very rapidly and is
cates a significant cost advantage over the life of
further reduced by the impedance of the medium-
the transformer, the designer will determine the
to-low voltage transformer. Low-voltage motor
cost of transformer losses, using the energy rates
feedback is considered only when calculating the
at the installation under design, and incorporate
short-circuit currents on the secondary system
loss requirements in the project specification. The
common to the motor and its source transformer(s).
c. Design of station. The initial design of new
project specification may also include provision for
rebates to the Government if loss requirements are
stations will include provisions to facilitate the
not met, and additional payment to the Contractor
addition of future lines, transformers, and associ-
if loss requirements are exceeded.
ated equipment to minimize the expense for sta-
b. Voltage regulators. Voltage regulation will be
tion expansion in later years. The area, fencing,
provided when required to obtain acceptable volt-
grounding and station arrangement will be such
4-8
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