The work on the principle of Faraday’s law of electromagnetic induction whenever the conductor cuts the magnetic flux and emf in induced in it. This emf is dimensionally induced emf. The direction of emf is found by Fleming Right hand Rule.
The nature of this emf is A.C. so it called A.C. generator. Instate of commentator the slip ring and brushes are given.
The system of stationary magnetic field and rotating conductor is adopted for very small capacity generators. It is not so popular for high voltage generator. The other most popular generator is the armature conductors are stationary and magnetic field is related mechanically.