A. no-load and greatly over-excited fields
B. no-load and under-excited fields
C. normal load with minimum excitation
D. normal load with zero excitation
Related Mcqs:
- A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?
A. remain same
B. go down
C. improve
D. none of the above - A synchronous motor can operate at____________?
A. lagging power factor only
B. leading power factor only
C. unity power factor only
D. lagging, leading and unity power factors - The standard full-load power factor ratings for synchronous motors are___________?
A. zero or 0.8 leading
B. unity or 0.8 lagging
C. unity or 0.8 leading
D. unity or zero - If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
A. will become more
B. will become less
C. will remain unchanged
D. none of the above. - If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________?
A. become more
B. become less
C. remain constant
D. none of the above - Synchronous motors are generally not self-starting because:
A. the direction of rotation is not fixed
B. the direction of instantaneous torque reverses after half cycle
C. startes cannot be used on these machines
D. starting winding is not provided on the machines - The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________?
A. zero degree
B. two degrees
C. five degrees
D. ten degrees - Mostly, synchronous motors are of_____________?
A. alternator type machines
B. induction type machines
C. salient pole type machines
D. smooth cylindrical type machines - Synchronous motors are_____________?
A. not-self starting
B. self-starting
C. essentially self-starting
D. none of the above - A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?
A. no change of power factor
B. lagging power factor with over-excitation
C. leading power factor with under-excitation
D. leading power factor with over-excitation
