文档介绍：Massachusetts Institute of Technology
Department of Electrical Engineering puter Science
Electric Machines
Class Notes 1: ic Forces February 11, 2004
c 2003 James L. Kirtley Jr.
1 Introduction
Stator
Bearings
Stator
Conductors
Rotor
Air
Gap
Rotor
Shaft End Windings Conductors
Figure 1: Form of Electric Machine
This section of notes discusses some of the fundamental processes involved in electric machinery.
In the section on energy conversion processes we examine the two major ways of estimating elec-
ic forces: those involving thermodynamic arguments (conservation of energy) and field
methods (Maxwell’s Stress Tensor). But first it is appropriate to introduce the topic by describing
a notional rotating electric machine.
Electric es in many different types and a strikingly broad range of sizes, from
those little machines that cause cell telephones and pagers to vibrate (yes, those are rotating electric
machines) to turbine generators with ratings upwards of a Gigawatt. Most of the machines with
which we are familiar are rotating, but linear electric motors are widely used, from shuttle drives in
weaving machines to equipment handling and amusement park rides. Currently under development
are large linear induction machines to be used to launch aircraft. It is our purpose in this subject
to develop an analytical basis for understanding how all of these different machines work. We start,
however, with a picture of perhaps the mon of electric machines.
2 Electric Machine Description:
Figure 1 is a cartoon drawing of a conventional induction motor. This is a mon type
of electric machine and will serve as a reference point. Most other electric machines operate in
1
a fashion which is the same as the induction machine or which differ in ways which are easy to
reference to the induction machine.
Most (but not all!) machines we will be studying have essentially this morphology. The rotor
of the machine is mounted on a shaft