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AC Single Phase Motors

Single phase motors are the most familiar of all electric motors because they are extensively used in home appliances, shops, offices etc. It is true that single phase 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. Here, we shall focus our attention on the construction, working and characteristics of commonly used single-phase motors.

Types of Single Phase AC Motors

Single-phase motors are generally built in the fractional-horsepower range and may be classified into the following  types:

I. Induction Type Motors 
  1. Split Phase Induction Motor
    1. Resistance Start
    2. Capacitor Start
    3. Capacitor Start Capacitor Run
    4. Permanent Capacitor 
  2. Shaded Pole Induction Motor
  3. Repulsion Start Induction Motor
II. Commutator Motors
  1. AC Series Motor
  2. Universal Motor
  3. Repulsion Type Motors
    1. Repulsion Start Induction Run
    2. Repulsion Induction Motor
III. Synchronous Motors
  1. Reluctance Motor
  2. Hysteresis Motor
Types of AC Single Phase Motors

Single Phase and Three Phase Motors - Comparison

A brief comparison between three phase and single phase motors are given below.
  1. Single phase induction motors are simple in construction, reliable and economical for small power rating as compared to three phase induction motors.
  2. The electrical power factor of single phase induction motors is low as compared to three phase induction motors.
  3. For same size, the single phase induction motors develop about 50% of the output as that of three phase induction motors.
  4. The starting torque is also low for asynchronous motors.
  5. The efficiency of single phase induction motors is less as compare it to the three phase induction motors.