We know the theory, that when there is relative motion between a conductor and a magnetic field that is magnetic field cuts conductor, then there some voltage is produced in the conductor. This is well known to all as Faraday’s laws of electromagnetic induction.
DC generator basics
Now by Faraday’s law the arrangement of conductor moving in a magnetic filed (that is a generator) produces alternating current and voltage. To avail DC voltage, current some extra mechanical arrangement is added to the output section. With this extra mechanical arrangement, the ac generator become a DC generator producing DC current.
Basic AC generator
Basic machine on Principle of Faraday’s law. It produces by naturally alternating current. The rotating machine supply ac power to static or stationary copper brush that collect current from rotating slip ring. In modern alternator or ac generator this arrangement is not used, as it has stator rotating. In modern machine stator remains stationary as it is heavier and bulkier and the rotor makes to rotate.
How DC generator works:
An special mechanical coupling – the commutator or split rings makes current flows in one direction, thus creating DC current. So the speed rotation of DC generator is a considerable fact and each dc generator has its operating speed.