Difference Between Synchronous and Asynchronous Motor

The difference between synchronous motor and the asynchronous motor is explained considering some factors using its type, slip, power source, the requirement of slip ring and brushes, cost, power factor, efficiency, speed, self stating, the current supply, various application, operational speed are listed below by using their comparisons. 


Definition of synchronous motor:


A synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. N = NS = 120f/P. Synchronous motor is not self-starting. 


Definition of asynchronous motor:


An asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous motor. N< NS. An asynchronous motor is self-starting.


The main key difference between  synchronous and an asynchronous motor is listed below:


  • A  synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. While the asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed.
  • The synchronous motor does not have a slip. The value of slip is zero. The asynchronous motor has slip therefore the value of slip is not equal to zero.
  • Synchronous motor is costly as compared to an asynchronous motor.
  • The efficiency of a synchronous motor is greater than the asynchronous motor.
  • The current is given to the rotor of the synchronous motor. The rotor of the asynchronous motor does not require any current.
  • Slip ring and brushes are required in a synchronous motor, whereas an asynchronous motor does not require a slip ring and brushes. Only would type induction motor require both slip ring and brushes are required.
  • Synchronous motor is not self-starting,  Asyncnous motor is self-starting.
  • The speed of the synchronous motor does not depend on the variation in the load. The speed of the asynchronous motor decreases with some load is increasing.
  • The synchronous motor requires an additional DC power source to initially rotate the rotor near to the synchronous speed. The asynchronous motor does not require any additional starting source.
  • Brushless motor, variable reluctance motor, switched reluctance motor, and hysteresis motor is the type of synchronous motor. AC induction motor is a type of asynchronous motor.
  • By changing excitation the power of the synchronous motor can be adjusted accordingly as lagging, leading, or unity, whereas the asynchronous motor runs only at lagging power factor.
  • Synchronous motor-operated smoothly and relatively good at low speed that is below 300 rpm, while the asynchronous motor-operated 600 rpm speed motor operation is excellent.
  • Synchronous motor is used in power stations, manufacturing industries, etc. It is also used, voltage controller. The asynchronous motor used in centrifugal pumps and fans, paper blowers, textile mills, compressors, and lifts, etc.
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