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The armature reaction is produced mainly by- a)load current in armature
- b)load current in field
- c)any of the mentioned
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The armature reaction is produced mainly by
a)
load current in armature
b)
load current in field
c)
any of the mentioned
d)
none of the mentioned
|
Sandeep Saha answered |
The armature reaction is initiated by the loaded conditions of the machine because an unloaded dc machine does not armature flux to get distorted.
Mark the most incorrect. In dc generator, commutation can be improved by- a)using interpoles
- b)using carbon brushes
- c)shifting brush axis in direction of armature rotation
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Mark the most incorrect. In dc generator, commutation can be improved by
a)
using interpoles
b)
using carbon brushes
c)
shifting brush axis in direction of armature rotation
d)
none of the mentioned
|
Pranjal Datta answered |
All the given measures are used to eliminate the effect of armature reaction and hence improves commutation also.
Each of the following is valid for interpoles except- a)they are connected in parallel with the armature so that they carry part of armature current
- b)they are small yoke fixed poles spaced in between main poles
- c)their polarity, in case of generator is same as that of main poles ahead
- d)they automatically neutralize not only reactance voltage but cross-magnetization also
Correct answer is option 'A'. Can you explain this answer?
Each of the following is valid for interpoles except
a)
they are connected in parallel with the armature so that they carry part of armature current
b)
they are small yoke fixed poles spaced in between main poles
c)
their polarity, in case of generator is same as that of main poles ahead
d)
they automatically neutralize not only reactance voltage but cross-magnetization also
|
Tanvi Rane answered |
All the options are valid for the interpoles except a because they are connected in series not in parallel.
The compensating winding in dc generator is provided to- a)neutralize cross-magnetizing flux
- b)neutralize demagnetizing flux
- c)neutralize armature mmf
- d)maintain magnetizing mmf
Correct answer is option 'A'. Can you explain this answer?
The compensating winding in dc generator is provided to
a)
neutralize cross-magnetizing flux
b)
neutralize demagnetizing flux
c)
neutralize armature mmf
d)
maintain magnetizing mmf
|
Muskaan Nair answered |
The compensating winding functions such that to nullify the cross magnetization effects in the armature.
The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation.- a)forward
- b)reverse to rotation
- c)any of the mentioned
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation.
a)
forward
b)
reverse to rotation
c)
any of the mentioned
d)
none of the mentioned
|
|
Sandeep Chatterjee answered |
For the generator, the electromagnetic torque produced is in the opposite direction and so the induced current. So to eliminate the sparking the brushes should be shifted in the forward direction of rotation.
The brushes are placed- a)along geometrical neutral axis
- b)perpendicular to geometrical neutral axis
- c)along magnetic neutral axis
- d)perpendicular to magnetic neutral axis
Correct answer is option 'A'. Can you explain this answer?
The brushes are placed
a)
along geometrical neutral axis
b)
perpendicular to geometrical neutral axis
c)
along magnetic neutral axis
d)
perpendicular to magnetic neutral axis
|
Rahul Chatterjee answered |
In order to achieve the sparkless commutation, the brushes on the commutator should be placed at the points known as neutral point where no voltage exists between adjacent segments. The conductors connected to these segments lie between the poles in position of zero magnetic flux which is termed as magnetic neutral axis (MNA).
The absence of compensating winding lead to- a)statically induced emf in armature
- b)fluctuations in supply
- c)reduction in the flux
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The absence of compensating winding lead to
a)
statically induced emf in armature
b)
fluctuations in supply
c)
reduction in the flux
d)
any of the mentioned
|
Harshad Singh answered |
The static emf induced inside gets reduced due to the armature reaction in large machines when there is no compensating winding present.
The coil under going commutation lies along _____ while the coil getting short circuited lies along ____ for a practical dc machine.- a)gna, mna
- b)mna, gna
- c)gna, gna
- d)mna, mna
Correct answer is option 'A'. Can you explain this answer?
The coil under going commutation lies along _____ while the coil getting short circuited lies along ____ for a practical dc machine.
a)
gna, mna
b)
mna, gna
c)
gna, gna
d)
mna, mna
|
Madhurima Das answered |
In a practical dc machine, the coil undergoing commutation lies along GNA so as the brushes and the coils which actually get short circuited lies along mna. This lead to sparking as a voltage difference is created at the coils.
With no commutating poles used the brushes are given backward lead in the dc motor.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
With no commutating poles used the brushes are given backward lead in the dc motor.
a)
True
b)
False
|
Poulomi Ahuja answered |
The armature reaction flux at the trailing edge weakens the flux and at the leading edge is strengthens the flux in the dc motor.
The number of compensating conductors/pole faces is _______ where Z is the number of active armature conductors/pole; A is number of parallel paths;(Ia is the armature current)- a)Z/A*Ia
- b)2*A*Ia/Z
- c)Z*Ia/A
- d)Z/2A*Ia
Correct answer is option 'A'. Can you explain this answer?
The number of compensating conductors/pole faces is _______ where Z is the number of active armature conductors/pole; A is number of parallel paths;(Ia is the armature current)
a)
Z/A*Ia
b)
2*A*Ia/Z
c)
Z*Ia/A
d)
Z/2A*Ia
|
|
Naveen Kapoor answered |
Compensating conductors per pole face is Z/A*Ia.
The commutation process involves basically reversal of current in armature coil as it crosses MNA.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
The commutation process involves basically reversal of current in armature coil as it crosses MNA.
a)
True
b)
False
|
|
Sandeep Chatterjee answered |
By reversing the current direction in the MNA the current can be limited in the coils to avoid sparking.
A 400-V, 1000-A, lap wound dc machine has 10 poles, 860 armature conductors. The number of conductors in the pole face to give full compensation if pole face covers 70% of pole span is- a)3010
- b)4300
- c)2400
- d)2800
Correct answer is option 'A'. Can you explain this answer?
A 400-V, 1000-A, lap wound dc machine has 10 poles, 860 armature conductors. The number of conductors in the pole face to give full compensation if pole face covers 70% of pole span is
a)
3010
b)
4300
c)
2400
d)
2800
|
|
Anuj Rane answered |
AT/pole for the compensating winding = 0.7*(Z*I/2P)
= 0.7*(860*100/2*10)
= 3010 AT.
= 0.7*(860*100/2*10)
= 3010 AT.
If the critical commutation time is 2 ms but it was observed that the practical commutation took 2.5 ms. This is the case of- a)under commutation
- b)over commutation
- c)critical commutation
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
If the critical commutation time is 2 ms but it was observed that the practical commutation took 2.5 ms. This is the case of
a)
under commutation
b)
over commutation
c)
critical commutation
d)
none of the mentioned
|
Avik Saha answered |
Since the time taken is more than the prescribed time limit for the commutation, it is under commutation.
The principle contributors to magneto motive force is/are- a)field current and armature current
- b)field excitation
- c)electromagnetic torque
- d)all of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The principle contributors to magneto motive force is/are
a)
field current and armature current
b)
field excitation
c)
electromagnetic torque
d)
all of the mentioned
|
|
Isha Singh answered |
The interaction between the field excitation and armature supply create the mmf and the interconnected behaviour creates the emf.
If the magnetic circuit of the dc machine is in the saturation region, the armature reaction- a)does not affect flux/pole
- b)increases the flux/pole
- c)decreases flux/pole
- d)affects the flux/pole only when armature current is small
Correct answer is option 'A'. Can you explain this answer?
If the magnetic circuit of the dc machine is in the saturation region, the armature reaction
a)
does not affect flux/pole
b)
increases the flux/pole
c)
decreases flux/pole
d)
affects the flux/pole only when armature current is small
|
|
Vaibhav Mukherjee answered |
In the saturation region the flux will be constant.
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