In principle, how is an alternating current waveform generated by a hydro-electric generator?
A DC current is applied to the field windings of the rotor. This DC current produces a magnetic field about the rotor. As the rotor turns, the magnetic field rotates and induces a voltage in the stator. The voltage induced in the stator causes current to flow out of the stator to the load connected to the generator. The magnitude of the voltage induced in the stator is determined by the strength of the DC current applied to the rotor field winding.