PRINCIPLES, CHARACTERISTICS, AND MANAGEMENT OF AC GENERATORS (ALTERNATORS)

96. Types of ac generators. The different types of ac generators (alternators), classified according to the method of producing the voltage, are listed below:

1. Synchronous alternators

   1. Revolving field

   2. Revolving armature

2. Induction alternators

   1. Stator winding

   2. Rotor winding

3. Inductor alternators

97. Synchronous ac generators are discussed in an elementary way in Secs. 73, 115, 144, 145, 148, and 152 of Div. 1. These generators may be constructed with either the armature or the field structure as the revolving member. Small generators up to 50 kW are commonly made with the revolving-armature construction. The required magnetic field is produced by dc electromagnets, which are excited as a small dc generator or exciter. The fundamental construction and connections for a revolving-field alternator are shown in Fig. 7.49.

FIGURE 7.49: Elementary diagram of an ac generator and exciter.

98. The emfin a synchronous alternator is generated as suggested in Fig. 7.50. As each field coil, D for instance, sweeps past the armature coils, the lines of flux from the field coil cut the armature coils. As coil D passes from A to C,an alternating emf represented by the curve ABC will be generated in the armature. It should be understood that in commercial alternators the armature coils are set in slots and arranged differently from those shown in Fig. 7.50, which only illustrate a principle.

FIGURE 7.50: Armature and field...