396 Electrical Power Systems Technology
cific signal polarity is applied. Also, the amount of torque developed by a
servomotor must be quite high. As a general rule, the torque developed is
a function of the voltage and current source.
Of the two distinct types of servomotors in use today, an AC type of
motor, called a synchronous motor, is commonly used in low-power ap-
plications. Excessive amounts of heat developed during starting condi-
tions normally limit this motor to rather low-output-power applications.
DC stepping motors are also used as servomotors.
ELECTRIC MOTOR APPLICATIONS
Certain factors must be considered when an electric motor is selected
for a specific application. Among these considerations are (1) the source
voltage and power capability available, (2) the effect of the power factor
and efficiency of the motor on the overall system, (3) the effect of the start-
ing current of the motor on the system, (4) the effect of the power system
on the operation of the motor, (5) the type of mechanical load, and (6) the
expected maintenance the motor will require.
Motor Performance
The major consumer of electrical power is the electric motor. It is es-
timated that electric motors account for 50 percent of the electrical power
consumed in industrial usage, and that 35 percent of all the electrical pow-
er used is used by electrical motors. For these reasons, we must consider
the efficient operation of motors to be a major part of our energy conserva-
tion efforts.
Both efficiency and the power factor must be considered in order
to determine the effect of a motor, in terms of efficient power conversion.
Remember the following relationships. First,
Pout × 100
Efficiency (%) = ——————
Pin
where:
Pin = the power input in horsepower, and
Pout = the power output in watts.
(To convert horsepower to watts, remember that 1 horsepower = 746