Synchronous motors

[amp_mcq option1=”d.c. source” option2=”armature input” option3=”motor input” option4=”supply lines” correct=”option2″]

Detailed SolutionThe rotor copper losses, in a synchronous motor, are met by

[amp_mcq option1=”connected to D.C. supply” option2=”short-circuited by low resistance” option3=”supply B. short-circuited by low resistance C. kept open-circuited” option4=”none of the above” correct=”option1″]

Detailed SolutionWhile starting a synchronous motor by induction motor action, field winding is usually

[amp_mcq option1=”number of poles” option2=”flux density” option3=”rotor speed” option4=”rotor excitation” correct=”option2″]

Detailed SolutionThe back e.m.f. in the stator of a synchronous motor depends on

[amp_mcq option1=”when under loaded” option2=”while over-excited” option3=”only at synchronous speed” option4=”below or above synchronous speed” correct=”option3″]

Detailed SolutionA synchronous motor can develop synchronous torque

[amp_mcq option1=”60 to 70%” option2=”75 to 80%” option3=”85 to 95%” option4=”99 to 99.5%” correct=”option3″]

Detailed SolutionThe efficiency of a properly designed synchronous motor will usually fall in range

[amp_mcq option1=”the direction of rotation is not fixed” option2=”the direction of instantaneous torque reverses after half cycle” option3=”startes cannot be used on these machines” option4=”starting winding is not provided on the machines” correct=”option2″]

Detailed SolutionSynchronous motors are generally not self-starting because

[amp_mcq option1=”supplied with unbalanced voltage” option2=”under-loaded” option3=”over-loaded” option4=”none of the above” correct=”option1″]

Detailed SolutionIn a 3-phase synchronous motor, the negative phase sequence exists when the motor is

[amp_mcq option1=”augments it directly” option2=”directly opposes it” option3=”cross-magnetises it” option4=”none of the above” correct=”option3″]

Detailed SolutionWhen a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way

[amp_mcq option1=”zero” option2=”45°” option3=”90°” option4=”120°” correct=”option3″]

Detailed SolutionThe power developed by a synchronous motor will be maximum when the load angle is

[amp_mcq option1=”voltage rating” option2=”current rating” option3=”power factor” option4=”speed” correct=”option1″]

Detailed SolutionTo limit the operating temperature an electrical machine should have proper