Electric motors provide the driving power for a large and still increasing
part of our modern industrial economy. The range of sizes and types of
motors is large and the number and diversity of applications continues
to expand. The computer on which this book is typed, for example, has
several electric motors inside, in the cooling fan and in the disk drives.
There is even a little motor that is used to eject the removable disk from
All around us there are electrical devices that move things around.
Just about everything in one’s life that whine, whirrs or clicks does so
because an electric motor caused the motion.
At the small end of the power scale are motors that drive the hands
in wristwatches, a job that was formerly done by a mechanical spring
mechanism. At the large end of the power scale are motors, rated in the
hundreds of megawatts (MW), that pump water uphill for energy storage.
Somewhat smaller motors, rated in the range of 12 to 15 MW, have
taken over the job of propulsion for cruise ships—a job formerly done by
steam engines or very large, low speed diesel engines.
The flexibility of electric motors and generators and the possibility of
transmitting electric power from place to place makes the use of electric
motors in many drive mechanisms attractive. Even in situations in which
the prime mover is aboard a vehicle, as in diesel-electric locomotives or
passenger ships, electric transmission has displaced most mechanical
or hydraulic transmission. As well, because electric power can be delivered over sliding contacts, stationary power plants can provide
motive power for rail vehicles. The final drive is, of course, an electric
The expansion of the use of electric motors’ industrial, commercial
and consumer applications is not at an end. New forms of energy storage
systems, hybrid electric passenger vehicles, and other applications not
yet envisioned will require electric motors, in some cases motors that
have not yet been invented.
This book provides a basic and in-depth explanation for the operation
of several different classes of electric motor. It also contains information
about motor standards and application. The book is mostly concerned
with application of motors, rather than on design or production. It takes,
however, the point of view that good application of a motor must rely on
understanding of its operation.