1. ln a synchronous motor which loss varies with load ?

Windage loss

Bearing friction loss

Copper loss

Core loss

Answer: Copper loss

Explanation:


2. A synchronous motor will always stop when ?

supply voltage fluctuates

load in motor varies

excitation winding gets disconnected

supply voltage frequency changes

Answer: excitation winding gets disconnected

Explanation:


3. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor ?

remains same as the original value

decreases to half the original value

tends to becomes zero

increases to two times the original value

Answer: increases to two times the original value

Explanation:


4. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?

Stator flux

Pull in torque

Both (a) and (b)

None of the above

Answer: None of the above

Explanation:


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

connected to D.C. supply

short-circuited by low resistance

kept open-circuited

none of the above

Answer: short-circuited by low resistance

Explanation:


6. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because ?

speed of the motor is reduced

power factor is decreased

Eb (back e.m.f.) becomes less than V (applied voltage)

Er (net resultant voltage) in armature is increased

Answer: Er (net resultant voltage) in armature is increased

Explanation:


7. If one-phase of a 3-phase synchronous motor is short-circuited, motor ?

will refuse to start

will overheat in spots

will not come up to speed

will fail to pull into step

Answer: will refuse to start

Explanation:


8. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will ?

stop

run as induction motor

function as static condenser

burn with dense smoke

Answer: stop

Explanation:


9. Exciters of synchronous machines are ?

d.c. shunt machines

d.c. series machines

d.c. compound machines

any of the above

Answer: d.c. shunt machines

Explanation:


10. In a synchronous motor, V-curves represent relation between ?

armature current and field current

power factor and speed

field current and speed

field current and power factor

Answer: armature current and field current

Explanation: