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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