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All questions of Basics for Electrical Engineering (EE) Exam
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 'D'. 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
 | EduRev GATE answered |
d) none of the mentioned
Let's break down each option:
- a) using interpoles: Interpoles (or commutating poles) are used in DC generators to improve commutation by neutralizing the effect of armature reaction. This option is correct.
- b) using carbon brushes: Carbon brushes are used to ensure good electrical contact with the commutator. Using carbon brushes is a standard practice and can contribute to improving commutation, so this option is correct.
- c) shifting brush axis in direction of armature rotation: Shifting the brush axis in the direction of armature rotation can also help in improving commutation, as it compensates for the armature reaction and minimizes sparking. This is also correct.
- d) none of the mentioned: Since options a), b), and c) are correct methods of improving commutation, this option is incorrect.
Thus, the most incorrect option is:
d) none of the mentioned
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.
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.
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.
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).
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.
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 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 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 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.
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 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
 | Raghav Nambiar answered |
The coil undergoing commutation and the coil getting short circuited are two different coils in a practical DC machine. These coils have different positions relative to the armature core and the commutator segments.
The coil undergoing commutation is the coil that is connected to the commutator segments at the moment when the brushes make contact with the segments. This coil is in the process of transferring the current from the armature winding to the external circuit. During this process, the coil experiences a change in the direction of current flow, which is known as commutation.
On the other hand, the coil getting short circuited is the coil that is connected to the brushes at the moment when the brushes lose contact with the commutator segments. This coil is short circuited and does not contribute to the output of the machine.
To summarize, in a practical DC machine:
- The coil undergoing commutation lies along the commutator segments.
- The coil getting short circuited lies along the brushes.
These positions are crucial for the proper operation of the machine and to ensure smooth commutation. The coil undergoing commutation must be in contact with the commutator segments to transfer the current to the external circuit effectively. The coil getting short circuited is disconnected from the external circuit to prevent any short circuiting and to allow the commutation process to occur smoothly.
Proper commutation is essential for the efficient operation of a DC machine. It ensures that the current in the armature winding remains unidirectional and the machine generates a steady output. The coil undergoing commutation and the coil getting short circuited play crucial roles in achieving this proper commutation.
The coil undergoing commutation is the coil that is connected to the commutator segments at the moment when the brushes make contact with the segments. This coil is in the process of transferring the current from the armature winding to the external circuit. During this process, the coil experiences a change in the direction of current flow, which is known as commutation.
On the other hand, the coil getting short circuited is the coil that is connected to the brushes at the moment when the brushes lose contact with the commutator segments. This coil is short circuited and does not contribute to the output of the machine.
To summarize, in a practical DC machine:
- The coil undergoing commutation lies along the commutator segments.
- The coil getting short circuited lies along the brushes.
These positions are crucial for the proper operation of the machine and to ensure smooth commutation. The coil undergoing commutation must be in contact with the commutator segments to transfer the current to the external circuit effectively. The coil getting short circuited is disconnected from the external circuit to prevent any short circuiting and to allow the commutation process to occur smoothly.
Proper commutation is essential for the efficient operation of a DC machine. It ensures that the current in the armature winding remains unidirectional and the machine generates a steady output. The coil undergoing commutation and the coil getting short circuited play crucial roles in achieving this proper commutation.
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.
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.
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