single phase motors
Chapter (9)
Single-Phase Motors
Introduction
As the name suggests, these motors are used on single-phase supply. Singlephase motors are the most familiar of all electric motors because they are extensively used in home appliances, shops, offices etc. It is true that singlephase motors are less efficient substitute for 3-phase motors but 3-phase power is normally not available except in large commercial and industrial establishments. Since electric power was originally generated and distributed for lighting only, millions of homes were given single-phase supply. This led to the development of single-phase motors. Even where 3-phase mains are present, the single-phase supply may be obtained by using one of the three lines and the neutral. In this chapter, we shall focus our attention on the construction, working and characteristics of commonly used single-phase motors.
9.1 Types of Single-Phase Motors
Single-phase motors are generally built in the fractional-horsepower range and may be classified into the following four basic types:
1.
Single-phase induction motors
(i) split-phase type
(iii) shaded-pole type
(ii) capacitor type
2.
A.C. series motor or universal motor
3.
Repulsion motors
(i) Repulsion-start induction-run motor
(ii) Repulsion-induction motor
4.
Synchronous motors
(i) Reluctance motor
(ii) Hysteresis motor
9.2 Single-Phase Induction Motors
A single phase induction motor is very similar to a 3-phase squirrel cage induction motor. It has (i) a squirrel-cage rotor identical to a 3-phase motor and
(ii) a single-phase winding on the stator.
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Unlike a 3-phase induction motor, a single-phase induction motor is not selfstarting but requires some starting means. The single-phase stator winding produces a magnetic field that pulsates in strength in a sinusoidal manner. The field polarity reverses after each half cycle but the field does not rotate.
Consequently, the alternating flux cannot
Single-Phase Motors
Introduction
As the name suggests, these motors are used on single-phase supply. Singlephase motors are the most familiar of all electric motors because they are extensively used in home appliances, shops, offices etc. It is true that singlephase motors are less efficient substitute for 3-phase motors but 3-phase power is normally not available except in large commercial and industrial establishments. Since electric power was originally generated and distributed for lighting only, millions of homes were given single-phase supply. This led to the development of single-phase motors. Even where 3-phase mains are present, the single-phase supply may be obtained by using one of the three lines and the neutral. In this chapter, we shall focus our attention on the construction, working and characteristics of commonly used single-phase motors.
9.1 Types of Single-Phase Motors
Single-phase motors are generally built in the fractional-horsepower range and may be classified into the following four basic types:
1.
Single-phase induction motors
(i) split-phase type
(iii) shaded-pole type
(ii) capacitor type
2.
A.C. series motor or universal motor
3.
Repulsion motors
(i) Repulsion-start induction-run motor
(ii) Repulsion-induction motor
4.
Synchronous motors
(i) Reluctance motor
(ii) Hysteresis motor
9.2 Single-Phase Induction Motors
A single phase induction motor is very similar to a 3-phase squirrel cage induction motor. It has (i) a squirrel-cage rotor identical to a 3-phase motor and
(ii) a single-phase winding on the stator.
227
Unlike a 3-phase induction motor, a single-phase induction motor is not selfstarting but requires some starting means. The single-phase stator winding produces a magnetic field that pulsates in strength in a sinusoidal manner. The field polarity reverses after each half cycle but the field does not rotate.
Consequently, the alternating flux cannot