Synchronous Motor | MCQ November 23, 2018Ajay Sharma 1. In a synchronous motor, damper winding is provided in order to stabilize rotor motion suppress rotor oscillations develop necessary starting torque suppress rotor oscillations and develop necessary starting torque Continue >>2. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on speed of the motor load on the motor both the speed and rotor flux d.c. excitation only Continue >>3. An electric motor in which both the rotor and stator fields rotates with the same speed is called a/an ........motor. d.c. charge synchronous universal Continue >>4. While running, a synchronous motor is compelled to run at synchronous speed because of damper winding in its pole faces magnetic locking between stator and rotor poles induced e.m.f. in rotor field winding by stator flux compulsion due to Lenz’s law Continue >>5. The direction of rotation of a synchronous motor can be reversed by reversing current to the field winding supply phase sequence polarity of rotor poles none of the above Continue >>6. When running under no-load condition and with normal excitation, armature current Ia drawn by a synchronous motor leads the back e.m.f. Eb by a small angle is large lags the applied voltage V by a small angle lags the resultant voltage ER by 90º. Continue >>7. The angle between the synchronously-rotating stator flux and rotor poles of a synchronous motor is called........ angle. synchronizing torque power factor slip Continue >>8. If load angle of a 4-pole synchronous motor is 8º (elect), its value in mechanical degrees is 4 2 0.5 0.25 Continue >>9. The maximum value of torque angle a in a synchronous motor is ........degrees electrical. 45 90 between 45 and 90 below 90 Continue >>10. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in its power factor torque angle back e.m.f. armature current. Continue >>11. When load on a synchronous motor running with normal excitation is increased, armature current drawn by it increases because back e.m.f. Eb becomes less than applied voltage V power factor is decreased net resultant voltage ER in armature is increased motor speed is reduced Continue >>12. When load on a normally-excited synchronous motor is increased, its power factor tends to approach unity become increasingly lagging become increasingly leading remain unchanged. Continue >>13. The effect of increasing load on a synchronous motor running with normal excitation is to increase both its Ia and p.f. decrease Ia but increase p.f. increase Ia but decrease p.f. decrease both Ia and p.f. Continue >>14. Synchronous capacitor is an ordinary static capacitor bank an over-excited synchronous motor driving mechanical load an over-excited synchronous motor running without mechanical load none of above Continue >>15. If the field of a synchronous motor is underexcited, the power factor will be lagging leading unity more than unity Continue >>16. Ignoring the effects of armature reaction, if excitation of a synchronous motor running with constant load is decreased from its normal value, it leads to increase in Eb but decrease in Ia increase in both Ia and p.f. which is lagging increase in both Ia and φ increase in Ia and Eb Continue >>17. A synchronous motor connected to infinite busbars has at constant full-load, 100% excitation and unity p.f. On changing the excitation only, the armature current will have leading p.f. with under-excitation leading p.f. with over-excitation lagging p.f. with over-excitation no change of p.f. Continue >>18. The V-curves of a synchronous motor show relationship between excitation current and back e.m.f. field current and p.f. d.c. field current and a.c. armature current armature current and supply voltage. Continue >>19. When load on a synchronous motor is increased, its armature currents is increased provided it is normally-excited over-excited under-excited all of the above Continue >>20. If main field current of a salient-pole synchronous motor fed from an infinite bus and running at no-load is reduced to zero, it would come to a stop continue running at synchronous speed run at sub-synchronous speed run at super-synchronous speed Continue >>21. In a synchronous machine when the rotor speed becomes more than the synchronous speed during hunting, the damping bars develop synchronous motor torque d.c. motor torque induction motor torque induction generator torque Continue >>22. In a synchronous motor, the rotor Cu losses are met by motor input armature input supply lines d.c. source Continue >>23. A synchronous machine is called a doubly-excited machine because it can be overexcited it has two sets of rotor poles both its rotor and stator are excited it needs twice the normal exciting current. Continue >> Synchronous Motor | MCQResult PLAY AGAIN !Please share it, your one share can change my life.