Synchronous motors

31. The rotor copper losses, in a synchronous motor, are met by

d.c. source
armature input
motor input
supply lines

Detailed SolutionThe

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

32. While starting a synchronous motor by induction motor action, field winding is usually

connected to D.C. supply
short-circuited by low resistance
supply B. short-circuited by low resistance C. kept open-circuited
none of the above

Detailed SolutionWhile

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

33. The back e.m.f. in the stator of a synchronous motor depends on

number of poles
flux density
rotor speed
rotor excitation

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synchronous motor depends on"
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class="read-more button" href="https://exam.pscnotes.com/mcq/the-back-e-m-f-in-the-stator-of-a-synchronous-motor-depends-on/#more-45131">Detailed SolutionThe back e.m.f. in the stator of a synchronous motor depends on

34. A synchronous motor can develop synchronous torque

when under loaded
while over-excited
only at synchronous speed
below or above synchronous speed

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class="read-more button" href="https://exam.pscnotes.com/mcq/a-synchronous-motor-can-develop-synchronous-torque/#more-45120">Detailed SolutionA synchronous motor can develop synchronous torque

35. The efficiency of a properly designed synchronous motor will usually fall in range

60 to 70%
75 to 80%
85 to 95%
99 to 99.5%

Detailed Solution

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class="screen-reader-text">The efficiency of a properly designed synchronous motor will usually fall in range

36. Synchronous motors are generally not self-starting because

the direction of rotation is not fixed
the direction of instantaneous torque reverses after half cycle
starting winding is not provided on the machines

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class="read-more-container">Detailed SolutionSynchronous motors are generally not self-starting because

37. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is

supplied with unbalanced voltage
under-loaded
over-loaded
none of the above

Detailed SolutionIn a 3-phase synchronous

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motor, the negative phase sequence exists when the motor is

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

augments it directly
directly opposes it
cross-magnetises it
none of the above

Detailed Solution

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class="screen-reader-text">When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way

39. The power developed by a synchronous motor will be maximum when the load angle is

zero
45°
90°
120°

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is" class="read-more button" href="https://exam.pscnotes.com/mcq/the-power-developed-by-a-synchronous-motor-will-be-maximum-when-the-load-angle-is/#more-44418">Detailed SolutionThe power developed by a synchronous motor will be maximum when the load angle is

40. To limit the operating temperature an electrical machine should have proper

voltage rating
current rating
power factor
speed

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href="https://exam.pscnotes.com/mcq/to-limit-the-operating-temperature-an-electrical-machine-should-have-proper/#more-44374">Detailed SolutionTo limit the operating temperature an electrical machine should have proper

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