Most ac current motors produce voltage through the use of power-generating systems, ashore and afloat. For this reason a majority of the motors used throughout the world are designed to operate on ac. There are other advantages in the use of ac motors besides the wide availability of ac power. In general, ac motors cost less than dc motors. Some types of ac motors do not use brushes and commutators. This eliminates many problems of maintenance and wear. It also eliminates the problem of dangerous sparking.
AC-current-motors are particularly well suited for constant-speed applications. This is because its speed is determined by the frequency of the ac voltage applied to the motor terminals. The dc motor is better suited than an ac motor for some uses, such as those that require variable- speeds. An ac motor can also be made with variable speed characteristics but only within certain limits.
Industry builds ac motors in different sizes, shapes, and ratings for many different types of jobs. These motors are designed for use with either polyphase or single-phase power systems. It is not possible here to cover all aspects of the subject of ac motors. Only the principles of the most commonly used types are dealt with in this chapter.
In this chapter, ac motors will be divided into (1) series,
(2) synchronous, and (3) induction motors. Single-phase and polyphase motors
will be discussed.
Synchronous motors, for purposes of this chapter, may be
considered as polyphase motors, of constant speed, whose rotors are energized
with dc voltage. Induction motors, single-phase or polyphase, whose rotors are
energized by induction, are the most commonly used ac motor.
The series ac motor, in a sense, is a familiar type of
motor. It is very similar to the dc motor and will serve as a bridge between the
old and the new.
AC phases and rotating magnetic fields
Three phase rotating fields in an ac current motor
Rotor-Behavior in a rotating field and synchronous motors.
Induction-motors in ac current motors
Single-phase and split-phase induction motors
Split-phase, capacitor-phase, and resistance-phase induction ac motors
Shaded-pole and speed of single-phase induction ac motors