What is the differences between synchronous and asynchronous motor?

• Synchronous motor runs only at one speed ((i.e) synchronous speed) which is determined by the number of poles in the machine and the frequency of power supply. If load exceeds the maximum value that the motor can take, it will come to halt.
• Asynchronous motor also known as induction motor runs at a lower speed than the synchronous speed depending on the load on the motor.

Sysnchronus Motors have constant magnetic field in the rotor these cannot use induction windings for starting. These motors require a variable-frequency power source to start. The main difference between a permanent magnet synchronous motor and an asynchronous motor is the rotor

Synchronous motor always runs at a speed equal to its synchronous speed i.e speed of rotation of magnetic field of stator.Induction motor always runs at a speed which is less than the synchronous speed.

Synchronous motor always runs at a speed equal to its synchronous speed.Induction motor always runs at a speed which is less than the synchronous speed.

• Synchronous motors require an additional DC power source for energizing rotor winding. Induction motors do not require any additional power source. Synchronous motors require additional starting mechanism to initially rotate the rotor near to the synchronous speed. No starting mechanism is required in induction motors.The power factor of a synchronous motor can be adjusted to lagging, unity or leading by varying the excitation, whereas, an induction motor always runs at lagging power factor.

All induction motors are asynchronous motors. The asynchronous nature of induction-motor operation comes from the slip between the rotational speed of the stator field and somewhat slower speed of the rotor. A more-specific explanation of how this slip arises gets into details of the motor internals.

A synchronous motor runs at a speed which is synchronised to the frequency of the AC voltage that supplies it, i.e  the rotor and stator run at the same speed.

but An asynchronous motor generally runs rotor slower than the stator.there is a slip resulting from different losses(copper,iron,friction,air gap,...etc.) for examle

3-phase induction motor

A synchronous motor has a special rotor construction that lets it rotate at the same speed — that is, in synchronization — with the stator field.

AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.called asynchronous motor.

synchronous motor drive in constant speed ,but asynchronous motor decrees some speed with load variation

a)The self-energized synchronous engine, additionally called an exchanged hesitance engine, contains a rotor cast of steel that incorporates indents or teeth, named remarkable shafts. It is the indents that let the rotor lock in and keep running at the same pace as the pivoting attractive field.

b)asynchronous motor run slower than the above with the rate that normally changes

• Synchronous motors require an additional DC power source for energizing rotor winding. Induction motors do not require any additional power source.
• Slip rings and brushes are required in synchronous motors, but not in Induction motors (except wound type induction motor in which slip ring motors are used to add external resistance to the rotor winding).
• Synchronous motors require additional starting mechanism to initially rotate the rotor near to the synchronous speed. No starting mechanism is required in induction motors.
• The power factor of a synchronous motor can be adjusted to lagging, unity or leading by varying the excitation, whereas, an induction motor always runs at lagging power factor.
• Synchronous motors are generally more efficient than induction motors.
• Synchronous motors are costlier.

 a synchronous motor run at a speed which is synchronised to frequency of ac voltage supplied to it ex: motor is supplied at frequency 60 hz then it will run at 603020 etc rev/sec depend on number of magnetic pole (246)

a asynchronous motor run slower than the above with the speed that usually varies