Difference Between Synchronous Motor And Induction Motor On the Basis Of Different Factor,
Synchronous Speed
Synchronous Motor: Operate at RPM=120f/p
Induction Motor: Operate at less than synchronous speed (RPM=120f/p – slip)
DC Excitation
Synchronous motors require DC excitation to be supplied to the rotor windings
Induction motors don’t require DC excitation to be supplied to the rotor windings
DC Power Source
Synchronous motors require a DC power source for the rotor excitation.
Induction motors don’t require a DC power source for the rotor excitation.
Rotor Excitation
Synchronous motors require slip rings and brushes to supply rotor excitation.
induction motors don’t require slip rings, but some induction motors have them for soft starting or speed control.
Rotor Winding
Synchronous motors require rotor windings
Induction motors are most often constructed with conduction bars in the rotor that are shorted together at the ends to form a “squirrel cage.”
Starting Mechanism
Synchronous motors require a starting mechanism in addition to the mode of operation that is in effect once they reach synchronous speed.
Three phase induction motors can start by simply applying power, but single phase motors require an additional starting circuit.
Power factor
The power factor of a synchronous motor can be adjusted to be lagging, unity or leading
Induction motors must always operate with a lagging power factor.
Efficiency
Synchronous motors are generally more efficient than induction motors.
Induction motors are generally less efficient than synchronous motors.
Slip
Synchronous motors can be constructed with permanent magnets in the rotor eliminating the slip rings, rotor windings, DC excitation system and power factor adjustability.
Induction motors contain slip.
Size
Synchronous motors are usually built only is sizes larger than about 1000 Hp (750 kW) because of their cost and complexity. However, permanent magnet synchronous motors and electronically controlled permanent synchronous motors called brushless DC motors are available in smaller sizes.
Smaller induction motors are built and commonly in household applications.
Application
Synchronous motor: Timing applications such as in synchronous clocks, timers in appliances, tape recorders, and precision servomechanisms
induction motor: Three-phase squirrel-cage induction motors are widely used in industrial drives because they are rugged, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans.
