hi readers, check out this new post on dc generators hope it will be useful to you guys...
1) In a dc machine the armature mmf is
A) stationary with respect to the field poles but rotating with respect to the armature
B) rotating with respect to field poles as well as armature
C) rotating with respect to field poles
D) stationary with respect to armature.
Ans:A
2) In a lap wound dc generator having P poles and Z conductors the maximum number of equalizer rings will be
A) Z/P
B) 2Z/P
C) Z/2P
D) Z/4P
Ans:A
3) Due to magnetic saturation, the flux per pole in a dc machine without brush shift
A) increases in both the generators and the motors with load.
B) decreases in both the generators and the motors with load.
C) increases in generators but decreases in motors with load.
D) decreases in generators but increases in motors with load.
Ans:B
4) In a dc machine, on no load the magnetic neutral axis
A) moves from geometrical neutral axis in the direction of rotation
B) moves from geometrical neutral axis in the opposite direction of rotation
C) coincides with the geometrical neutral axis
D) none of the above
Ans:C
5) Pole shoe of a dc machine is laminated for the purpose of
A) decreasing hysteresis loss
B) decreasing eddy current loss
C) decreasing both hysteresis and eddy current loss
D) manufacturing ease
Ans:B
6) Sparking commutation can be achieved by employing
A) interpoles
B) compensating winding
C) high resistance carbon brushes
D) any one or more of the above methods
Ans:D
7) Under-commutation results in
A) sparking at the middle of the brush
B) sparking at the leading edge of the brush
C) sparking at the trailing edge of the brush
D) no sparking
Ans:C
8) 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) economic on the material required for interpoles and their windings
D) increase the accelerating of commutation
Ans:B
9) The compensating windings are placed in the slots in the pole faces to neutralize the
A) cross-magnetizing effect
B) demagnetizing effect
C) both of the demagnetizing and cross-magnetizing effects
D) armature reaction mmf under the pole faces and avoid flash over between positive and negative brushes
Ans:D
10) In dc machines, the interpoles are provided
A) for mechanical balance of machines
B) to counteract the demagnetizing effect of armature mmf in the commutating zone
C) to counteract the reactance voltage and the cross-magnetizing effect of armature mmf in the commutating zone
D) to make commutation sparkless
E) both (C) and (D)
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1) In a dc machine the armature mmf is
A) stationary with respect to the field poles but rotating with respect to the armature
B) rotating with respect to field poles as well as armature
C) rotating with respect to field poles
D) stationary with respect to armature.
Ans:A
2) In a lap wound dc generator having P poles and Z conductors the maximum number of equalizer rings will be
A) Z/P
B) 2Z/P
C) Z/2P
D) Z/4P
Ans:A
3) Due to magnetic saturation, the flux per pole in a dc machine without brush shift
A) increases in both the generators and the motors with load.
B) decreases in both the generators and the motors with load.
C) increases in generators but decreases in motors with load.
D) decreases in generators but increases in motors with load.
Ans:B
4) In a dc machine, on no load the magnetic neutral axis
A) moves from geometrical neutral axis in the direction of rotation
B) moves from geometrical neutral axis in the opposite direction of rotation
C) coincides with the geometrical neutral axis
D) none of the above
Ans:C
5) Pole shoe of a dc machine is laminated for the purpose of
A) decreasing hysteresis loss
B) decreasing eddy current loss
C) decreasing both hysteresis and eddy current loss
D) manufacturing ease
Ans:B
6) Sparking commutation can be achieved by employing
A) interpoles
B) compensating winding
C) high resistance carbon brushes
D) any one or more of the above methods
Ans:D
7) Under-commutation results in
A) sparking at the middle of the brush
B) sparking at the leading edge of the brush
C) sparking at the trailing edge of the brush
D) no sparking
Ans:C
8) 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) economic on the material required for interpoles and their windings
D) increase the accelerating of commutation
Ans:B
9) The compensating windings are placed in the slots in the pole faces to neutralize the
A) cross-magnetizing effect
B) demagnetizing effect
C) both of the demagnetizing and cross-magnetizing effects
D) armature reaction mmf under the pole faces and avoid flash over between positive and negative brushes
Ans:D
10) In dc machines, the interpoles are provided
A) for mechanical balance of machines
B) to counteract the demagnetizing effect of armature mmf in the commutating zone
C) to counteract the reactance voltage and the cross-magnetizing effect of armature mmf in the commutating zone
D) to make commutation sparkless
E) both (C) and (D)
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