Properties of Saturated Steam Data. Honeywell AUTOMATIC CONTROL SI Edition

GENERAL ENGINEERING DATA

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.

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.

Motor Type

Universal

(Series)

Table 18. Single-Phase Motor Characteristics and Applications.

Characteristics

Armature and field connected in series. Operates on dc or ac with approximately the same speed and torque.

Split-Phase

Starting

Capacitor

Starting

Shaded-Pole

Starting

Repulsion

Starting

Uses a pair of field windings for starting with one winding slightly lagging. One winding is disconnected by a centrifugal switch when running speed is reached.

Same as split-phase with a capacitor connected to the winding that stays on line. Provides greater starting torque with high efficiency and power factor.

A short-circuited winding is used on each pole piece along with a normal winding. Magnetic flux in the shorted turn produces starting torque. Torque is low.

Operates as a repulsion motor on starting and a centrifugal 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.

Application

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.

VOLTAGE CONVERSION

Existing Voltage

EMS Effective

Average

Peak

Peak-to-Peak

EMS Effective

—

1.110

0.707

0.354

Table 19. Voltage Conversion Multipliers.

Average

0.900

—

0.637

0.318

Desired Voltage

Peak

1.414

1.570

—

0.500

Peak-to-Peak

2.828

3.141

2.000

—

ENGINEERING MANUAL OF AUTOMATIC CONTROL

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