The rotor in a power generator has a speed limit, in essence, and as a result, can only produce, at most, about 22,000 volts of power (22kV). In order to produce much more voltage, power stations employ the use of a transformer. Transformers “transform” electricity from one voltage to another and are capable of both stepping up the voltage of a generator as well as stepping it down. At the power station, power is stepped up to deliver upwards of 765,000 volts (765 kV) across high power lines (though most high voltage lines in use are 550kV).
A transformers work changes voltages when the incoming wire is wrapped around an iron core – known as the primary winding. This creates a magnetic field through the core. The outgoing wire (the secondary winding) is wrapped around the other side of the core. For a step up transformer where voltage is increased, the outgoing wire is wrapped several more times around the core than the incoming wire. By doubling the windings, the voltage is doubled. In turn, ten times the number of windings on the secondary coil will produce 10 times the voltage.
Thus, a 22kv input from the power station can be stepped up to incredible voltages, though typically not more than 765 kv as the powerlines themselves have capacity limits. These lines can then be run to a high voltage transmission line for delivery across vast distances. Once it is ready for delivery, the power can then be stepped down in a similar manner. To deliver power to homes for instance, power can be stepped down in a serious of substation transformers then finally to a pole transformer for residential use where the power is finally stepped down to a usable 110 to 220 volts.