An electric generator is a device that creates electrical current using the principles of the electromagnetic effect. In the simplest of terms, a generator is actually a very large magnet spinning inside a large number of coils of wire.
Key components of a generator include the following:
- The shaft that is spun by an external force such as a steam turbine, gas turbine, or wind turbine
- The rotor, which is an electromagnet that is turned by the shaft
- The rotor winding, which is wire that covers the rotor
- An exciter, which creates a magnetic field in the rotor winding by applying DC current (called the excitation current)
- Slip rings that carry the current from the rotor winding to the rotor to create the magnetic field in the rotor (a slip ring is a device that makes an electrical connection between a stationary object and a rotating object)
- The stator, which is a stationary metallic ring that surrounds the rotor
- The armature (also called the stator winding), which comprises loops of wire around the stator
When the turbine spins the shaft, the corresponding movement of the rotor creates an induced voltage in the armature. If the armature is connected to a complete circuit, the induced voltage creates an electric current. This current is then fed into a transmission line.
Since utility transmission systems operate as three-phase systems with three wires conducting the electricity, it is necessary to wind three conductors in the stator (indicated by blue, red, and green in the above diagram). The conductors are insulated from each other with the result that three phases of power are created, corresponding to the three phases transmitted on the transmission line. Multiple stator windings increase the magnitude of the generated voltage.