TMS-811-1/AFJMAN
32-1080
Table 3-2. Nominal System Voltages.
plated voltage increase, transformers for use in
kV primary distribution systems may be more
ongoing construction will be specified to have dual
economical. Primary distribution voltages of the
primary voltages, when economic and transformer
nominal 7.5 kV class and under will not be used,
delivery time considerations permit such a require-
unless an off-site supply of a higher voltage is not
ment. When a dual voltage, high-voltage trans-
available. Seldom is the lower voltage advanta-
former is specified, taps are not normally available
geous. For such cases, the size of the installation
for the lower voltage. For existing voltage drop
and the distances involved must make the use of
problems, not having transformer taps available
voltages below 7.5 kV more economical in order to
may create an untenable situation, requiring a
justify the selection.
facility boost transformer, or other means to serve
3-4. Selection of Primary Distribution Voltage
the facility until the distribution system is up-
for Existing Installations.
graded. If the facility to be added is not included
in the master plan, an engineering study will be
When small facilities are added to an installation,
necessary to determine the most feasible method of
the primary distribution system voltage within the
providing service. Acquisition or preparation of
addition will match the existing system. However,
maps of transmission and distribution systems
if the addition is substantial and large voltage
with distances between principle points and single
drops or line losses can occur when existing volt-
line diagrams of the systems will be required.
ages are retained, or if the main electric supply
Then a determination of the extent to which the
station is inadequate, then the economics of a
existing system voltage can satisfy installation
higher voltage for the primary distribution system
requirements, or the economics of a higher voltage
must be taken into account. The electrical master
level and benefits of such a system will be evalu-
plan should have already provided for such defi-
ated.
ciencies. When a master plan indicates a contem-
3-2
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