Multiple choice questions on dc generator # 14

                            Hi friends, this is objectives on dc generator which has been asked in IES previous papers check out and comment if you have any doubts....

1) The interpoles in dc machine have a tapering shape in order to
A) Reduce the overall weight
B) Reduce the saturation in the interpole
C) Economies on the material required for interpoles and their winding
D) Increase the acceleration of commutation

Ans:B

2) A dc shunt motor is excited from an alternating power frequency voltage source. Its brush axis is rotated by an angle 𝞪 from geometrical neutral axis. The torque developed will be proportional to which one of the following?
A) sin 𝞪
B) cos 𝞪
C) tan 𝞪
D) cos 2𝞪

Ans: B

3) To have sparkless commutation, the armature reaction effect in a dc machine is neutralized by
A) compensating winding and commutating poles
B) shifting the brush axis from geometrical neutral axis to magnetic neutral axis
C) fixing the brush axis in line with the pole axis
D) increasing the field excitation

Ans:A

4) In large sized dc machine the compensating winding are provided to
A) compensate for the decrease in speed due to increase of load
B) neutralize the voltage induced in the coil due to high fluctuation of load
C) reduce eddy current losses by providing local short-circuits
D) none of the above

Ans:B

5) If the brushes are given a small amount of forward shift  in case of a dc generator, the armature reaction effect will be
A) totally demagnetizing
B) totally cross-magnetizing
C) partly demagnetizing and partly cross-magnetizing
D) totally magnetizing

Ans:C

6) Armature reaction in a dc shunt generator, running at full load with the brushes not shifted from the geometrical neutral plane and saturation neglected is
A) absent
B) cross-magnetizing
C) demagnetizing
D) magnetizing

Ans:B

7) In a dc machine without any brush shift, the shift of the magnetic neutral axis owing to armature reaction is
A) in the direction of rotation for both the generator and the motor
B) against the direction of rotation for both the generator and the motor
C)  in the direction of rotation for  the generator and against the direction of rotation for the motor
D) against the direction of rotation for the generator and in the direction of rotation of motor

Ans:C

8) The armature mmf of a dc machine has
A) triangular space distribution and rotates at the speed of armature
B) trapezoidal space distribution and is stationary in space
C) stepped distribution and rotates at the speed of armature
D) triangular space distribution and is stationary in space

Ans:D

9) A 6 pole lap wound dc machine has 720 conductors and it draws 50 A from supply mains. what is the flux distribution produced by the armature reaction per pole?
A) Rectangular in wave shape with a peak of 500 AT
B) Rectangular in wave shape with a peak of 100 AT
C) Triangular in wave shape with a peak of 500 AT
D) Triangular in wave shape with a peak of 1000 AT

Ans:C

10) A frog-leg winding is used in a dc machine to eliminate
A) the use of equalizers in lap winding
B) the use of compensating winding
C) the use of interpole winding
D) reactance voltage produced due to commutation

Ans:A

      If you have any doubts please refer this posts...

• what is armature reaction?
• how to reduce armature reaction?
• Brief description about compensating winding

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