Civil engineering work associated with
the substation should be initiated as early as possible in order to
ensure that the best available site is selected. This work includes a
study of the topography and drainage patterns of the area together
with a subsurface soil investigation.
The information obtained from the
subsurface soil investigation also will be used to determine the
design of the substation foundations. For large substations or
substations located in area with poor soils, it may be necessary to
obtain additional subsurface soil tests after final selection of the
substation site has been made.
The additional information should fully
describe the quality of the soil at the site, since the data will be
used to design equipment foundations.
Open-Bus Arrangement.
An air-insulated, open-bus substation
arrangement consists essentially of open-bus construction using
either rigid- or strain-bus design such as the breaker-and-a-half
arrangement shown in Figure below; the buses are arranged to run the
length of the station and are located toward the outside of the
station. The transmission-line exits cross over the main bus and are
deadended on takeoff tower structures.
The line drops into the bay in the
station and connects to the disconnecting switches and circuit
breakers. Use of this arrangement requires three distinct levels of
bus to make the necessary crossovers and connections to each
substation bay.
Typical dimensions of these levels at
230 kV are 16 ft for the first level above ground, 30 ft high for the
main bus location, and 57 ft for the highest level of bus.
This arrangement, in use since the
mid-1920s and widely used by many electric utilities, has the
advantage of requiring a minimum of land area per bay and relative
ease of maintenance, and it is ideally suited to a transmission-line
through-connection where a substation must be inserted into a
transmission line.
Inverted Bus.
An alternate arrangement is the
inverted-bus, breaker-and-a-half scheme for EHV substations. With
this arrangement, all outgoing circuit takeoff towers are located in
the outer perimeter of the substation, eliminating the crossover of
line or exit facilities.
Main buses are located in the middle of
the substation, with all disconnecting switches, circuit breakers,
and bay equipment located outboard of the main buses. The end result
of the inverted-bus arrangement presents a very low profile station
with many advantages in areas where beauty and aesthetic qualities
are a necessity for good public relations.
The overall height of the highest bus
in the 230-kV station just indicated reduces from a height of 57 ft
above ground in the conventional arrangement to a height of only 30
ft above ground for the inverted bus low-profile scheme.
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