[amp_mcq option1=”Not-self starting” option2=”Self-starting” option3=”Essentially self-starting” option4=”None of the above” correct=”option1″]
Synchronous motors
22. If the field of a synchronous motor is underexcited, the power factor will be
[amp_mcq option1=”zero” option2=”unity” option3=”lagging” option4=”leading” correct=”option3″]
Detailed SolutionIf the field of a synchronous motor is underexcited, the power factor will be
23. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
[amp_mcq option1=”increase in both armature current and power factor angle” option2=”increase in back e.m.f. but decrease in armature current” option3=”increase in both armature current and power factor which is lagging” option4=”increase in torque angle but decrease in back e.m.f.” correct=”option1″]
24. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
[amp_mcq option1=”One-third” option2=”Twice” option3=”Thrice” option4=”Six times” correct=”option3″]
25. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
[amp_mcq option1=”Eddy current losses in the conductors” option2=”Iron losses in the stator” option3=”Copper losses in the slot portion of the conductors” option4=”Windage losses” correct=”option4″]
26. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
[amp_mcq option1=”Stator flux” option2=”Pull in torque” option3=”Both (A) and (B)” option4=”None of the above” correct=”option3″]
27. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
[amp_mcq option1=”induction motor torque in field winding” option2=”induction motor torque in damper winding” option3=”eddy current and hysteresis torque in pole faces” option4=”reHetance motor torque due to saliency of the rotor E. all of the above methods” correct=”option3″]
28. The coupling angle or load angle of synchronous motor is defined as the angle between the
[amp_mcq option1=”rotor and stator teeth” option2=”rotor and the stator poles of opposite polarity” option3=”rotor and the stator poles of the same polarity” option4=”none of the above” correct=”option3″]
29. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
[amp_mcq option1=”synchronous motor has no slip” option2=”stator supply is not required to produce magnetic field” option3=”mechanical load on the rotor remains constant” option4=”synchronous motor has large airgap” correct=”option1″]
30. The power factor of a synchronous motor is better than that of induction motor because
[amp_mcq option1=”stator supply is relieved of responsibility of producing magnetic field” option2=”mechanical load on the motor can be adjusted” option3=”synchronous motor runs at synchronous speed” option4=”synchronous motor has large air gap” correct=”option1″]