characteristics of the synchronous motor is its constant speed
irrespective of the load conditions, and variable power factor
operation. As seen earlier its power factor can be controlled by
controlling its excitation. For overexcitation its power factor is
leading in nature, which is very important from the power factor
correction point of view.
Due to constant speed characteristics, it is used in machine tools,
motor generator sets, synchronous clocks, stroboscopic devices, timing
devices, belt driven reciprocating compressors, fans and blowers,
centrifugal pumps, vacuum pumps, pulp grinders, textile mills, paper
mills line shafts, rolling mills, cement mills etc.
The synchronous motors are often used as a power factor correction
device, phase advancers and phase modifiers for voltage regulation of
the transmission lines. This is possible because the excitation of the
synchronous motor can be adjusted as per the requirement.
The disadvantages of synchronous motor are their higher cost, necessity
of frequent maintenance and a need of d.c. excitation source, auxiliary
device or additional winding provision to make it self starting.
Overall their initial cost is very high.