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Old Posted Oct 1, 2010, 12:18 AM
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MSOE_superforce87 MSOE_superforce87 is offline
Student Engineer
Join Date: Jan 2007
Location: Milwaukee
Posts: 7
About power distribution:

Skyscrapers are different from most buildings because of their height. Because of this, plus the fact that there is a high demand for power, towers often use whats called a "medium" voltage service. What this means is that power is distributed throughout the building using AC voltages between 600V to 35,000V. At strategic locations in the building, these large power risers are tapped in whats called a substation. A typical substation will have a high voltage switch, transformer, and low voltage (480V, 277V, 208V, or 120V) switchboard. The purpose of the substations is to convert the high voltage into usable power (like 120 volt). Each substation can be rated up to 4,000 amps on the low voltage side and draws about 50 amps on the high voltage (600V-35kV) side depending on what voltage is chosen. That is why the large high voltage lines are used, they can provide the same amount of power with lower currents. Furthermore, when a long distance is needed such as a tall buildling, it is easier to manage power losses (cable resistance and high currents) by using higher voltage.

An example of this type of distribution is in a large local building. In the basement, utility service enters the building at 13,200V. Two sets of riser cables operating at 13,200V go up the building to substations located at different levels. The substations take in 13,200V and put out 480V, distributing the bulk power. Additional Transformers take this lower voltage (480V) bulk power down to 208/120V for lighting and smaller loads. Most of the motors and large loads operate on the 480V, and everything else is fed by the 208V transformers.

Hope this helps.
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