Polyphase system: How Three phase sytem works?

Three Phase system

   A three phase circuit is energized by three alternating emf's of the same frequency and differing in time phase by 120 .The emfs are generated in three sets of armature coils in an ac generator. These three sets are 120 degree apart on the generator armature. The coils may all be brought of the generator to form three separate single phase circuits. however the coils are ordinarily interconnected either internally or externally to form  a three-wire or four wire system.

shows the generation of induced emf in 3 spaced coils with 120 degree phase difference

    The voltage in red coil  reaches a maximum cycle first,followed by coil in yellow, and then coil in blue for sequence ABC.The figure also shows the sine wave developed as the coil rotates.

the voltage phase sequence of the three phase system can be determined by the rotation of the alternator coils. At  counterclockwise rotation of the coils, the phase sequence is ABC. The opposite rotation gives the sequence CBA