Application, advantages and disadvantages of synchronous motor

Application of synchronous motor:

1)     It is used in power houses and sub-stations in parallel to the bus bars to improve power factor. For this purpose, it is run without mechanical load on it and over excited.

2)   Large number of induction motors or transformers operating at lagging power factor, it is used for improving power factor.

3)      Generate electric power at power plants.

4)    Control the voltage at the end of transmission line by varying its excitation (DC supply).

5)        It is used in motor generator sets requiring constant speed.

6)    It is also used in rubber mills, textile mills, cement factories, air compressors, centrifugal pumps which requiring constant speed and Pulp beaters and grinders, steel and metal rolling mills, rock and ore crushers are generally coupled or geared to the motor.

Advantages of synchronous motor:

1)    Synchronous motors can be constructed with wider air gaps than induction motors which makes these motors mechanically more stable.

2)    In this motor, easy to insulate armature winding for high voltage for which alternator is designed.

3)   The ability to control the power factor is one of the major advantage of synchronous motor. An over excited synchronous motor can have leading power factor. It can be operated in parallel to induction motors and other lagging power factor loads thereby improving the system power factor.

4)       In synchronous motor the speed remains constant irrespective of the loads. This characteristic helps in industrial drives where constant speed is required irrespective of the load it is driving.

5)        In synchronous motors electro-magnetic power varies linearly with the voltage.

6)      Synchronous motors usually operate with higher efficiency (more than 90%) especially in low speed and unity power factor applications compared to induction motors.

7)        It also useful when the motor is required to drive another alternator to supply at a different frequency as in frequency changes.

Disadvantages of synchronous motor:

1)    It cannot be used for variable speed job as there is no possibility of speed adjustment.

2)         It requires d. c. excitation which must be supplied from external source.

3)         It cannot be started under loaded condition. Its starting torque is zero.

4)         It is not self-starting. Special methods are adopted to make it self-starting.

5)         Additional damper winding is necessary.

6)         Collector rings and brushes are required.

7)      It has a tendency to hunt.