Electrical Power Systems Technology

Alternating Current Power Systems 149

source through a slip ring/brush assembly to the windings of the rotor.

The magnetic polarities of the rotor, as shown, are north at the top and

south at the bottom of the illustration. The magnetic lines of force develop

around the outside of the electromagnetic rotor assembly.

Through electromagnetic induc-

tion, a current can be induced into

each of the stationary (stator) coils

of the generator. Since the beginning

of phase A is physically located 120°

from the beginning of phase B, the

induced currents will be 120° apart.

Likewise, the beginnings of phase B

and phase C are located 120° apart.

Thus, the voltages developed as a re-

sult of electromagnetic induction are

1200 apart, as shown in Figure 6-9.

Figure 6-8. Simplified drawing showing the basic construction of a three-phase

AC generator

Figure 6-9. Output waveforms

of a three-phase AC generator