Electrical power travels along transmission wires from power plants to homes and businesses. Along the way, transformers raise or "step up" and lower or "step down" the voltage.
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Electric Power Delivery System

Electric power supplied to homes and businesses is typically AC (alternating current). The electrons do not travel along the power lines overhead but vibrate back and forth at 60 times per second within these lines. The AC outlet in your home delivers energy not electrons. When you plug in an appliance, the outlet supplies the power to move electrons that are already in the wiring of the appliance, around a closed circuit to produce a current. The energy is supplied to your home as a voltage through a large and very complex power distribution network. After electric power is generated within a power station, it is sent through a network of power lines to consumers. This is done in several steps.

  • Electric power leaves the power plant at very high current levels and with voltages of several thousand volts.
  • The voltage is "stepped up" (increased) to several hundred thousand volts because less energy is lost during the trip along the overhead power lines at these high voltages.
  • Before the power is distributed to industrial users, the voltage is "stepped down" (decreased) to several thousand volts again.
  • For home use, the voltage is stepped down even further to 110 volts.

Each time the voltage is stepped down, a transformer is used. Transformers are devices that work only with alternating current flows to either step up or step down voltages. They begin to behave badly when direct currents (DC) are superimposed on the normal AC currents that are handled routinely in the power grid. This is the main reason that power grids can be compromised by space weather events.

Last modified February 17, 2009 by Randy Russell.

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