Page 28 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

Source: ELECTRICAL EQUIPMENT HANDBOOK

CHAPTER 2
INTRODUCTION TO

MACHINERY PRINCIPLES

ELECTRIC MACHINES AND TRANSFORMERS

An electric machine is a device that can convert either mechanical energy to electric energy
or electric energy to mechanical energy. Such a device is called a generator when it con-
verts mechanical energy to electric energy. The device is called a motor when it converts
electric energy to mechanical energy. Since an electric machine can convert power in either
direction, such a machine can be used as either a generator or a motor. Thus, all motors and
generators can be used to convert energy from one form to another, using the action of a
magnetic field.
A transformer is a device that converts ac electric energy at one voltage level to ac elec-
tric energy at another voltage level. Transformers operate on the same principles as gener-
ators and motors.

COMMON TERMS AND PRINCIPLES

angular position of an object. It is the angle at which it is oriented. It is mea-
sured from one arbitrary reference point (units: rad or deg).
angular velocity d /dt. It is the rate of variation of angular position with time
(units: rad/s or deg/s).
f angular velocity, expressed in revolutions per second /2 .
m m
angular acceleration d /dt. It is the rate of variation of angular velocity with
2
time (units: rad/s ).
torque (force applied) (perpendicular distance). Units are newton-meters
(N m)
Newton’s law of rotation:
J
2
where J is the moment of inertia of the rotor (units: kg m ).
W work T , if T is constant (units: J).
P power dW/dt. It is the rate of variation of work with time (units: W):
P T

2.1
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