Construction of AC generator (Not for examination) Stator core Slot Rectangular loop Outlet terminal Stator core Stator winding Figure(c): Stator core with armature windings Salient pole Magnetic yoke Figure(d): -pole rotor Magnetic lines Salient pole Slip ring Brushes Excitation coil DC supply input Figure(e): -pole rotor with field windings, slip rings and brushes ± Figure(f): Stator core and rotor ii) Rotor Rotor contains magnetic field windings, slip rings and brushes mounted on the same shaft. Figure(a): Stator core with empty slots Figure(b): Stator core with rectangular loop Alternator consists of two major parts, namely stator and rotor. (This box is given for better understanding of constructional details) i) Stator Stator has two components, namely stator core and armature winding. 12th - 12th - - - - - Unit ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT The initial position of the field magnet is horizontal and field direction is perpendicular to the plane of the coil .
As it is seen in single phase AC generator, when field magnet is rotated from that position in clockwise direction, alternating emf ε in coil begins a cycle from origin O. This is shown in Figure . . The corresponding cycle for alternating emf ε in coil starts at point A after field magnet has rotated through °.
Therefore, the phase difference between ε and ε is °. Similarly, emf ε in coil would begin its cycle at point B after ° rotation of field magnet from initial position. Thus these emfs produced in the three phase AC generator have ° phase difference between one another. ° ° ° ° ° ° For coil , field magnet is in initial position at t= For coil , field magnet has to rotate through For coil , rotation of field magnet is required t t t Te dotted lines represent emfs induced in previous cycle Figure .
Variation of emfs ε ε ε , and with time angle. . . Advantages of three- phase alternator Three-phase system has many advantages