synchronous motors Mcqs
101. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in______________?
comments icon0
A. armature current

B. back e.m.f.

C. power factor

D. torque angle

102. The maximum power developed in a synchronous motor occurs at a coupling angle of____________?
comments icon0

A. 180

B. 90

C. 30

D. 60

103. The speed regulation of a synchronous motor is always___________?
comments icon0

A. 1%

B. zero

C. positive

D. 0.50%

104. The size of a synchronous motor decreases with the increase in___________?
comments icon0

A. all of the above

B. flux density

C. speed

D. horse power rating

105. In a synchronous motor, the damping winding is generally used to______________?
comments icon0

A. reduce noise level

B. provide starting torque only

C. none of the above

D. reduce the eddy currents

E. prevent hunting and provide the starting torque
106. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
comments icon0

A. power factor as well as armature current will increase

B. power factor as well as armature current will decrease

C. power factor will increase but armature current will decrease

D. power factor will decrease and armature current will increase
107. If one-phase of a 3-phase synchronous motor is short-circuited, motor will ______________?
comments icon0

A. will overheat in spots

B. will refuse to start

C. will not come upto speed

D. will fail to pull into step

108. The ratio of starting torque to running torque in a synchronous motor is____________?
comments icon0
A. zero

B. infinity

C. one

D. two

109. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________?
comments icon0

A. load on the motor

B. d.c. excitation only

C. both the speed and rotor flux

D. none of the above

110. The speed of a synchronous motor:
comments icon0

A. decreases as the load decreases

B. none of the above

C. increases as the load increases

D. always remains constant
111. A synchronous motor can be used as a synchronous capacitor when it is____________?
comments icon0

A. under-loaded

B. over-loaded

C. over-excited

D. under-excited

112. The rotor copper losses, in a synchronous motor, are met by____________?
comments icon0

A. armature input

B. supply lines

C. motor input

D. d.c. source
113. A three-phase synchronous motor will have_____________?
comments icon0
A. two slip-rings

B. three slip-rings

C. one slip-ring

D. no slip-rings

114. The oscillations in a synchronous motor can be damped out by_______________?
comments icon0

A. oscillations cannot be damped

B. providing damper bars in the rotor pole faces

C. maintaining constant excitation

D. running the motor on leading power factors

115. The standard full-load power factor ratings for synchronous motors are___________?
comments icon0

A. unity or zero

B. unity or 0.8 leading

C. zero or 0.8 leading

D. unity or 0.8 lagging

116. The magnitude of field flux in a 3-phase synchronous motor?
comments icon0

A. varies with speed

B. varies with the load

C. remains constant at all loads

D. varies with power factor

117. The effect of increasing the load on a synchronous motor running with normal excitation is to___________?
comments icon0

A. decrease both armature current and power factor

B. decrease armature current but increase power factor

C. increase armature current but decrease power factor

D. increase both its armature current and power factor

118. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
comments icon0
A. All of the above

B. Stator winding to earthed frame

C. Rotor winding to earthed shaft

D. Phase to phase winding resistance

119. The induced e.m.f. in a synchronous motor working on leading power factor will be_____________?
comments icon0

A. equal to the supply voltage

B. None of these

C. less than the supply voltage

D. more than the supply voltage
120. In which of the following motors the stator and rotor fields rotate simultaneously?
comments icon0

A. D.C. motor

B. Induction motor

C. Universal motor

D. Reluctance motor

E. Synchronous motor
121. The synchronous motor is not inherently self-starting because_______________?
comments icon0

A. the rotating magnetic field is produced by only 50 Hz frequency currents

B. the force required to accelerate the rotor to the synchronous speed in an instant is absent

C. the starting device to accelerate the rotor to near synchronous speed is absent

D. a rotating magnetic field does not have enough poles

122. As the load is applied to a synchronous motor, the motor takes more armature current because
comments icon0

A. the rotor strengthens the rotating field casuing more motor current

B. the rotor by shifting its phase backward causes motor to take more current

C. the increased load has to take more current

D. the back e.m.f. decreases causing an increase in motor current