SYNCHRONOUS GENERATOR CONSTRUCTION

A direct current is applied to the rotor winding of a synchronous generator to produce the rotor magnetic field. A prime mover causes the generator rotor to rotate the magnetic field in the machine. A three-phase set of voltages is induced in the stator windings by the rotating magnetic field.

The rotor is a large electromagnet. Its magnetic poles can be salient (protruding or sticking out from the surface of the rotor), as shown in Fig. 12.1 or nonsalient (flush with the surface of the rotor), as shown in Fig. 12.2. Two-and four-pole rotors have normally nonsalient poles, while rotors with more than four poles have salient-pole rotors.

Figure 12.1: ( a) A salient six-pole rotor for a synchronous machine. ( b) Photograph of a salient eightpole synchronous machine rotor showing the windings on the individual rotor poles. ( Courtesy of General Electric Company.) ( c) Photograph of a single salient pole from a rotor with the field windings not yet in place. ( Courtesy of General Electric Company.) ( d) A single salient pole shown after the field windings are installed but before it is mounted on the rotor. ( Courtesy of Westinghouse Electric Company.)

Figure 12.2: A nonsalient two-pole rotor for a synchronous machine.

Small generator rotors are constructed of thin laminations to reduce eddy current losses, while large rotors are...