Synchronous machines - Applications, Advantages and Disadvantages

We have already discussed Introduction to Synchronous Machines , Constructional Features of Synchronous Machines and Types of Synchronous Machines . in current article we are going to discuss applications, advantages and disadvantages of synchronous machines.

Application of Synchronous Machines

Synchronous machines are very important machinery in electrical engineering. Following are the important applications of a synchronous motors or machines : -

• 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.
• In factories having large number of induction motors or transformers operating at lagging power factor, it is used for improving power factor.
• It is used to generate electric power at power station, one of the most important application of synchronous machines.
• it is used to control the voltage at the end of transmission line by varying its excitation.
• It is also used in rubber mills, textile mills, cement factories, air compressors, centrifugal pumps which requiring constant speed.
• It is used in motor generator sets requiring constant speed.

Synchronous motors are mostly use to drive continuously operating and constant speed equipment such as centrifugal pumps, fans, blowers, ammonia and air compressors, motor-generator sets etc.

Advantages of Synchronous Machine

Being power factor improvement appliance synchronous machines posses lots of positive points. Some very important advantages are : -

• There motors can be made to operate at a leading power factor and thereby improve the power factor of an industrial plant from lagging to one that is close to unity.
• It gives constant speed from no load to full load.
• Electro-magnetic power varies linearly with voltage.
• These motors can be constructed with wider air gaps than induction motors, which make then better mechanically.
• These motors operates at higher efficiency, especially in the low speed unity power factor range.

Disadvantages of Synchronous Machines

Everything has its own advantages and disadvantages and Synchronous machine is not an exception. Synchronous machines has some disadvantages. Some of noticeable disadvantages or demerits of synchronous machines are as : -

• It cannot be used for variable speed job as there is no possibility of speed adjustment.
• It requires d. c. excitation which must be supplied from external source.
• It cannot be started under loaded condition. Its starting torque is zero.
• It has a tendency to hunt.
• It is not possible for places where frequent starting is required.
• It may fall out of synchronism and stop when over loaded.
• Collector rings and brushes are required.