Synchronous motors

[amp_mcq option1=”2″ option2=”3″ option3=”4″ option4=”6″ correct=”option1″]

Detailed SolutionIf load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is

[amp_mcq option1=”load on the motor” option2=”d.c. excitation only” option3=”both the speed and rotor flux” option4=”none of the above” correct=”option3″]

Detailed SolutionIn a synchronous motor, the magnitude of stator back e.m.f. Eb depends on

[amp_mcq option1=”zero degree” option2=”two degrees” option3=”five degrees” option4=”ten degrees” correct=”option2″]

Detailed SolutionThe mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of

[amp_mcq option1=”leading” option2=”lagging” option3=”unity” option4=”zero” correct=”option2″]

Detailed SolutionWhen the field of a synchronous motor is under-excited, the power factor will be

[amp_mcq option1=”the motor is said to be fully loaded” option2=”the torque generated is maximum” option3=”the excitation is said to be zero per cent” option4=”the excitation is said to be hundred per cent” correct=”option3″]

Detailed SolutionIn a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

[amp_mcq option1=”Damper winding” option2=”Star-delta starter” option3=”Damper winding in conjunction with star-delta starter” option4=”Resistance starter in the armature circuit” correct=”option3″]

Detailed SolutionWhich of the following methods is used to start a synchronous motor ?

[amp_mcq option1=”direct current” option2=”alternating current” option3=”no current” option4=”all of the above” correct=”option1″]

Detailed SolutionSlip-rings in a synchronous motor carry

[amp_mcq option1=”45°” option2=”60°” option3=”90°” option4=”120°” correct=”option1″]

Detailed SolutionA synchronous motor develops maximum power when load angle is

[amp_mcq option1=”the motor stops” option2=”it runs as a reluctance motor at the same speed” option3=”it runs as a reluctance motor at a lower speed” option4=”none of the above” correct=”option3″]

Detailed SolutionWhen the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected

[amp_mcq option1=”zero power factor leading” option2=”unity power factor” option3=”0.707 power factor lagging” option4=”0.707 power factor leading” correct=”option1″]

Detailed SolutionThe minimum armature current of the synchronous motor corresponds to operation at