Question

Which of the following is a disadvantage of synchronous motor over induction motor for power requirements from 35 kW up to about 2500 kW?
1. Cost
2. Size
3. Weight
4. Requirement of DC supply for field

Answer 1

Correct Answer - Option 4 : Requirement of DC supply for field

Comparison between Induction Motor and Synchronous Motor for power range 35 kW to 2500 kW:

Particular	Synchronous Motor	Induction Motor
Speed	Constant speed from no load to full load	Speed change with load
Power factor	Can be operated at all power factor	Operate at lagging power factor
Excitation	Required DC excitation at the rotor or filed	No need for excitation
Economy	Economical for speed below 500 RPM	Economical for speed above 600 RPM
Starting	Auxiliary means have to provide for starting	Self-starting
Construction	Complicated	Simple
Starting toque	More	Less