Electrical Power Systems Technology

Operational Power Control Systems 445

such as electric drills, sewing machines, electric mixers, and industrial ap-

plications.

FREQUENCY-CONVERSION SYSTEMS

The power system frequency used in the United State is 60 hertz, or

60 cycles per second. However, there are specific applications that require

other frequencies in order to operate properly. Mechanical frequency con-

verters may be used to change an incoming frequency into some other fre-

Figure 16-18. Dynamic braking circuit for a DC shunt motor

Figure 16-19. Dynamic braking circuit for a single-phase AC induction motor