Synchronous motors

[amp_mcq option1=”voltage booster” option2=”phase advancer” option3=”noise generator” option4=”mechanical synchronizer” correct=”option1″]

Detailed SolutionA synchronous motor working at leading power factor can be used as

[amp_mcq option1=”no slip-rings” option2=”one slip-ring” option3=”two slip-rings” option4=”three slip-rings” correct=”option1″]

Detailed SolutionA three-phase synchronous motor will have

[amp_mcq option1=”flux density” option2=”horse power rating” option3=”speed” option4=”all of the above” correct=”option4″]

Detailed SolutionThe size of a synchronous motor decreases with the increase in

[amp_mcq option1=”stator frame” option2=”rotor shaft” option3=”pole faces” option4=”none of the above” correct=”option3″]

Detailed SolutionIn a synchronous motor, damper windings are provided on

[amp_mcq option1=”will become more” option2=”will become less” option3=”will remain unchanged” option4=”none of the above.” correct=”option1″]

Detailed SolutionIf 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

[amp_mcq option1=”pull-up torque” option2=”pull-in torque” option3=”pull-out torque” option4=”none of the above” correct=”option2″]

Detailed SolutionThe maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as

[amp_mcq option1=”the synchronous speed” option2=”less than synchronous speed” option3=”more than synchronous speed” option4=”none of the above” correct=”option1″]

Detailed SolutionSynchronous motor always runs at

[amp_mcq option1=”the stator current will be zero” option2=”the stator current will be very small” option3=”the stator current will be very high” option4=”the back e.m.f. will be more than the supply voltage” correct=”option1″]

Detailed SolutionIf the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

[amp_mcq option1=”no-load and greatly over-excited fields” option2=”no-load and under-excited fields” option3=”normal load with minimum excitation” option4=”normal load with zero excitation” correct=”option1″]

Detailed SolutionFor power factor correction, synchronous motors operate at

[amp_mcq option1=”the force required to accelerate the rotor to the synchronous speed in an instant is absent” option2=”the starting device to accelerate the rotor to near synchronous speed is absent” option3=”a rotating magnetic field does not have enough poles” option4=”the rotating magnetic field is produced by only 50 Hz frequency currents” correct=”option1″]

Detailed SolutionThe synchronous motor is not inherently self-starting because