13 Rotating Machines
13.1 Elementary Concepts of Rotating Machines
13.2 Induction Machines
13.3 Synchronous Machines
13.4 Direct-Current Machines
13.5 Learning Objectives
13.6 Practical Application: A Case Study—Wind-Energy-Conversion Systems
Problems
The most widely used electromechanical device is a rotating machine, which utilizes the magnetic
field to store energy. The main purpose of most rotating machines is to convert electromechanical
energy, i.e., to convert energy between electrical and mechanical systems, either for electric power
generation (as in generators or sources) or for the production of mechanical power to perform
useful tasks (as in motors or sinks). Rotating machines range in size and capacity from small motors
that consume only a fraction of a watt to large generators that produce several hundred megawatts.
In spite of the wide variety of types, sizes, and methods of construction, all such machines operate
on the same principle, namely, the tendency of two magnets to align themselves.
Most space is devoted to induction, synchronous, and direct-current machines. In spite of the
distinguishing features peculiar to each class of machines, there are several striking similarities
among the main kinds of machines.
13.1 ELEMENTARY CONCEPTS OF ROTATING MACHINES
Some of the basic features of conventional ac (particularly synchronous) and dc machines have
been introduced in Chapter 12. More will be presented in this section. Three modes of operation of
a rotating electric machine—motoring, generating,andbraking—are illustrated in Figure 13.1.1.
- Themotoring modehas electric power input and mechanical power output. The electro-
magnetic torqueTedrives the machine against the load torqueT. The input voltagevdrives the
current into the winding against the generated emfe.
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