Electric Motors; Voltage Conversion - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

ELECTRIC MOTORS

Single-phase electric motors are classified by the method used
to start the motor. Table 18 describes the characteristics and
typical applications of single-phase motors by classification.
No special means of starting is required for three-phase motors,
since starting (rotational) torque is inherent in three-phase
motors. A three-phase motor can be reversed by switching any
two phases.
Motor Type
Universal Armature and field connected in series. Operates on dc or
(Series) ac with approximately the same speed and torque.
Split-Phase Uses a pair of field windings for starting with one winding
Starting slightly lagging. One winding is disconnected by a
centrifugal switch when running speed is reached.
Capacitor Same as split-phase with a capacitor connected to the
Starting winding that stays on line. Provides greater starting torque
with high efficiency and power factor.
Shaded-Pole A short-circuited winding is used on each pole piece along
Starting with a normal winding. Magnetic flux in the shorted turn
produces starting torque. Torque is low.
Repulsion Operates as a repulsion motor on starting and a centrifugal
Starting switch converts it to an induction motor when running speed
is reached. Motor has a commutator as in a dc motor.
Provides high starting torque.

VOLTAGE CONVERSION

Existing Voltage
EMS Effective
Average
Peak
Peak-to-Peak
ENGINEERING MANUAL OF AUTOMATIC CONTROL
Table 18. Single-Phase Motor Characteristics and Applications.
Characteristics
Table 19. Voltage Conversion Multipliers.
EMS Effective
—
1.110
0.707
0.354
Motors have two current ratings locked rotor (LRA) and full
load (FLA). Locked rotor current is drawn at the instant power
is applied and before the motor starts rotating. It is also drawn
if the motor is stalled. Full load current is drawn when the motor
is running at its full load rating.
Where either ac or dc may be available. Used for
portable tools, vacuum cleaners, electric
typewriters, etc.
Where starting torque and varying load are not
excessive. Used for oil burners, washing
machines, grinding wheels, etc.
Where high starting torque and heavy varying
loads exist. Used for air conditioners,
refrigerators, air compressors, etc.
Where starting torque is low and less than 1/20
horsepower is required. Used for electric clocks.
Where high starting torque is required. Used in
machine shops.
Desired Voltage
Average Peak
0.900 1.414
— 1.570
0.637
0.318 0.500
475
GENERAL ENGINEERING DATA
Application
Peak-to-Peak
2.828
3.141
— 2.000
—