Question { Jindal, 6066 }

Difference between induction motor and synchronous motor?

i Think Synchronous motors operate at synchronous speed
(RPM=120f/p) while induction motors operate at less than
synchronous speed (RPM=120f/p – slip). Slip is nearly zero
at zero load torque and increases as load torque increases

am a right pls guide & send Other Comments

Answer

Forget about slip first of all..
In synchronous motor the stator and room are magnetically locked, means production of exact opposite pole on room with respect to stator are produced.
Stator speed=rotor speed


But in case of indication motor it works on induction principle..
I.e to rotating rotor same poles will create on both stator and rotor. Thus stator opposite the rotor thus it will starts to rotating.
Stator speed =/>/< rotor speed. Based on application

Question { NTPC, 8319 }

why the transformer has no starter

Answer

Basically starter is used for purpose of limiting the starting current ther by it protect the equipment ( motor and generator)from high current , thus the windings of equipment are protected.
 
If no starter is used then the starting current will be huge which damage winding.
            I.e  v=ir, 
                    I= v/r
                    I=220/0.2 
                    I=1100Amp. which is dangerously high  

Where as in case of transformer to protect it from high inrush currents the windings are mechanically braced to with stand these forces.
That's way no starter is used.

                    AND 
Starter is used where breaking and starting operations occurred mostly.
     But if once we start the transformer we can't break it until any abnormal condition occurred.