# Working Principle & Starting Methods Of Synchronous Motor - MCQs

## Working Principle & Starting Methods Of Synchronous Motor - MCQs

Q1. If a three phase windings displaced in space by 120 degree in a synchronous motor then the magnitude of resultant flux when it is rotated by Θ = 0 degree and Θ = 60 degree is

a. 0, 1.5 times the magnitude of maximum flux
b. 1.5 times the magnitude of maximum flux, 0
c. 0.866 times the magnitude of maximum flux, 1.5 times the magnitude of maximum flux
d. 1.5 times the magnitude of maximum flux, 1.5 times the magnitude of maximum flux

ANSWER: d. 1.5 times the magnitude of maximum flux, 1.5 times the magnitude of maximum flux

Q2. For a half cycle of fluxes in a synchronous motor, the resultant flux has rotated through

a. 0 degree
b. 90 degree
c. 180 degree
d. 360 degree

ANSWER: c. 180 degree

Q3. For a two pole, 50 Hz, 3 phase synchronous motor the speed of rotating magnetic field is

a. 1000 rpm
b. 2000 rpm
c. 3000 rpm
d. 3500 rpm

ANSWER: c. 3000 rpm

Q4. A synchronous motor draws 2 MVA at a power factor of 0.8 leading. If the efficiency developed in the motor is 90% then the power developed is equal to

a. 1212 kW
b. 1440 kW
c. 1676 kW
d. 1767 kW

ANSWER: b. 1440 kW

Q5. Synchronous motor works on the principle of

a. Mutual induction
b. Electromagnetic induction
c. Magnetic locking
d. None of these

ANSWER: c. Magnetic locking

Q6. Synchronous motors are

a. Self starting
b. Not self starting

ANSWER: b. Not self starting

Q7. Can synchronous motor rotate at any speed other than the synchronous speed?

a. Yes
b. No

Q8. The method used for starting synchronous motor is/are

a. Using pony motors
b. Using damper windings
c. As a slip ring induction motor
d. All of the above

ANSWER: d. All of the above

Q9. A synchronous motor is started by using damper winding. When the motor will run at synchronous speed then the induced emf in the damper winding will be

a. Zero
b. Maximum
c. Half of the terminal voltage
d. None of these