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All questions of DC Machines for Electrical Engineering (EE) Exam
If the DC machine is held constant at 3000 rpm. The DC voltage is 250V and speed is 2950. If the field is held constant with 250V. Is this machine generator or motor?
- a)Motor
- b)Generator
- c)None of the mentioned
- d)Any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
If the DC machine is held constant at 3000 rpm. The DC voltage is 250V and speed is 2950. If the field is held constant with 250V. Is this machine generator or motor?
a)
Motor
b)
Generator
c)
None of the mentioned
d)
Any of the mentioned
|
Sravya Khanna answered |
From the speed and emf relation, E = 250*2950/3000
= 245.8 V
This is less than the terminal voltage. Hence it is a motor.
= 245.8 V
This is less than the terminal voltage. Hence it is a motor.
Which of the following equations represents the RMS value of the generated EMF in a short-pitched N-turn armature coil of an AC machine ____________- a)E = √2πkpfrNΦ
- b)E = 2πkpfrNΦ
- c)E = NΦωrkpsinωrt
- d)None of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Which of the following equations represents the RMS value of the generated EMF in a short-pitched N-turn armature coil of an AC machine ____________
a)
E = √2πkpfrNΦ
b)
E = 2πkpfrNΦ
c)
E = NΦωrkpsinωrt
d)
None of the mentioned
|
Sanvi Kapoor answered |
EMF induced = NΦωrkpsinωrt,
Emax = NΦωrkp when sinωrt = 1
RMS value, E = Emax/√2 = √2πfrkpNΦ
Emax = NΦωrkp when sinωrt = 1
RMS value, E = Emax/√2 = √2πfrkpNΦ
A shunt generator has an induced voltage on open circuit of 127 V. When the machine is on load the terminal voltage is 120 V. The load current if the field resistance be 15 ohm and armature resistance be 15 ohm- a)342 A
- b)350 A
- c)358 A
- d)8 A
Correct answer is option 'A'. Can you explain this answer?
A shunt generator has an induced voltage on open circuit of 127 V. When the machine is on load the terminal voltage is 120 V. The load current if the field resistance be 15 ohm and armature resistance be 15 ohm
a)
342 A
b)
350 A
c)
358 A
d)
8 A
|
Rajeev Menon answered |
Ia*Ra = E-V
= 127 – 120
= 7 V
Ia = 350 A
Ish = 120/15
= 8 A
I = 350 – 8
= 342 A
Which of the following statements is/are correct regarding the generation of EMF in rotating electrical machines in the armature winding? EMF is generated ____________- a)by rotating armature windings through a magnetic field
- b)by rotating magnetic field with respect to the armature windings
- c)by designing the magnetic circuit to have variable reluctance with rotor rotation
- d)any of the mentioned
Correct answer is option 'D'. Can you explain this answer?
Which of the following statements is/are correct regarding the generation of EMF in rotating electrical machines in the armature winding? EMF is generated ____________
a)
by rotating armature windings through a magnetic field
b)
by rotating magnetic field with respect to the armature windings
c)
by designing the magnetic circuit to have variable reluctance with rotor rotation
d)
any of the mentioned
|
Bijoy Kapoor answered |
Any of the above mentioned methods will produce EMF in the armature windings.
The voltage drop at brush-commutator contact is variable (1-2V) and dependent of armature current.- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
The voltage drop at brush-commutator contact is variable (1-2V) and dependent of armature current.
a)
True
b)
False
|
Sagarika Patel answered |
The voltage drop at brush-commutator contact is variable (1-2V) and independent of armature current.
Consider a DC generator running at the rated speed of 2000 rpm, suddenly there is an insulator falls on the field circuit and breaks it. Then- a)the motor stops in a few rounds
- b)it continues to run, but as dc motor
- c)it continues to run as a motor
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Consider a DC generator running at the rated speed of 2000 rpm, suddenly there is an insulator falls on the field circuit and breaks it. Then
a)
the motor stops in a few rounds
b)
it continues to run, but as dc motor
c)
it continues to run as a motor
d)
none of the mentioned
|
Lakshmi Desai answered |
As the field circuit gets broken there is interruption in the flux to the dc machine, and as a result the motor stops in few seconds.
What losses occur in the teeth of dc generator?- a)To reduce hysteresis loss
- b)To reduce eddy current loss
- c)To reduce eddy current as well as hysteresis losses
- d)To achieve high permeability
Correct answer is option 'C'. Can you explain this answer?
What losses occur in the teeth of dc generator?
a)
To reduce hysteresis loss
b)
To reduce eddy current loss
c)
To reduce eddy current as well as hysteresis losses
d)
To achieve high permeability
|
Avinash Mehta answered |
Copper Losses or Electrical Losses in DC Machine or Winding Loss. The copper losses are the winding losses taking place during the current flowing through the winding. These losses occur due to the resistance in the winding. In DC machine, there are only two winding, armature and field winding As we know “Energy neither can be created nor it can be destroyed, it can only be transferred from one form to another”. In DC machine, mechanical energy is converted into the electrical energy. During this process, the total input power is not transformed into output power.The copper losses are the winding losses taking place during the current flowing through the winding. These losses occur due to the resistance in the winding. In DC machine, there are only two winding, armature and field winding.To reduce eddy current as well as hysteresis losses
The shaft power at the DC Generator is- a)sum of mechanical power and rotational losses
- b)only mechanical losses
- c)no-load losses and mechanical power
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The shaft power at the DC Generator is
a)
sum of mechanical power and rotational losses
b)
only mechanical losses
c)
no-load losses and mechanical power
d)
any of the mentioned
|
Swara Dasgupta answered |
Explanation: The shaft power is sum of mechanical power and rotational losses.
correct answer is option A
Inspite of heavy initial investments, dc motors are used due to- a)flexibility and ease of control
- b)lower losses
- c)improved power factor of the system
- d)all of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Inspite of heavy initial investments, dc motors are used due to
a)
flexibility and ease of control
b)
lower losses
c)
improved power factor of the system
d)
all of the mentioned
|
|
Arya Mukherjee answered |
The control of dc machines is very much simplified when compared to other machines. So this makes it very useful when compared.
PMDC had no ________ excited machine.- a)electrically
- b)magnetically
- c)none of the mentioned
- d)least
Correct answer is option 'A'. Can you explain this answer?
PMDC had no ________ excited machine.
a)
electrically
b)
magnetically
c)
none of the mentioned
d)
least
|
Bhavana Reddy answered |
It has no electrical excitation.
The critical resistance refers to- a)the resistance above which machine does not excite
- b)the resistance below which machine does not excite
- c)the resistance at which machine does not excite
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The critical resistance refers to
a)
the resistance above which machine does not excite
b)
the resistance below which machine does not excite
c)
the resistance at which machine does not excite
d)
any of the mentioned
|
Lavanya Menon answered |
After taking a glance at the magnetization curve, it can be concluded that the emf will not build up if the resistance is greater than critical resistance.
Small DC motors have best speed control by- a)armature voltage control
- b)field resistance control
- c)any of the methods
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Small DC motors have best speed control by
a)
armature voltage control
b)
field resistance control
c)
any of the methods
d)
none of the mentioned
|
Yash Patel answered |
For the small dc motors it is difficult to vary the speed using their field control.
The manufacturer has mentioned a medium starting torque and 15% speed regulation. The most appropriate motor for his requirement is- a)dc shunt motor
- b)induction motor
- c)differential motor
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The manufacturer has mentioned a medium starting torque and 15% speed regulation. The most appropriate motor for his requirement is
a)
dc shunt motor
b)
induction motor
c)
differential motor
d)
none of the mentioned
|
Uday Saini answered |
The dc shunt motor provides a medium values of the torque.
Centrifugal pumps, fans-blowers use- a)shunt as well as induction motor
- b)only shunt motors
- c)only induction motor
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Centrifugal pumps, fans-blowers use
a)
shunt as well as induction motor
b)
only shunt motors
c)
only induction motor
d)
none of the mentioned
|
|
Yash Patel answered |
Centrifugal pumps, fans-blowers use shunt as well as induction motor.
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 possible causes of overheating of commutator in a DC machine.
- a)Any of the mentioned
- b)Restricted ventilation
- c)Shorted winding
- d)Overload
Correct answer is option 'A'. Can you explain this answer?
Mark the possible causes of overheating of commutator in a DC machine.
a)
Any of the mentioned
b)
Restricted ventilation
c)
Shorted winding
d)
Overload
|
|
Lavanya Menon answered |
All the factors can cause the overheating of commutator.
In the hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as motor?
- a)B
- b)A
- c)A,B
- d)None of the mentioned
Correct answer is option 'A'. Can you explain this answer?
In the hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as motor?
a)
B
b)
A
c)
A,B
d)
None of the mentioned
|
Sushant Mukherjee answered |
Correct answer is option A.
Ea/Eb = 1.4/1.3
Ea= 1.077 Eb > Eb
So, the machine will act as motor.
Ea/Eb = 1.4/1.3
Ea= 1.077 Eb > Eb
So, the machine will act as motor.
Why is armature of a dc machine made of silicon steel stampings?- a)To reduce hysteresis loss
- b)To reduce eddy current loss
- c)For the ease with which slots can be created
- d)To achieve high permeability
Correct answer is option 'A'. Can you explain this answer?
Why is armature of a dc machine made of silicon steel stampings?
a)
To reduce hysteresis loss
b)
To reduce eddy current loss
c)
For the ease with which slots can be created
d)
To achieve high permeability
|
|
Arya Mukherjee answered |
The silicon steel has very high permeability and makes the flux past consistent. Thereby making lesser losses.
If the electromagnetic torque in a DC shunt-generator is opposite, what can be further concluded?- a)Mechanical power is absorbed by the machine
- b)Mechanical power is delivered by the machine
- c)Electromagnetic torque is in same direction of prime mover
- d)None of the mentioned
Correct answer is option 'A'. Can you explain this answer?
If the electromagnetic torque in a DC shunt-generator is opposite, what can be further concluded?
a)
Mechanical power is absorbed by the machine
b)
Mechanical power is delivered by the machine
c)
Electromagnetic torque is in same direction of prime mover
d)
None of the mentioned
|
|
Sanvi Kapoor answered |
When the electromagnetic torque is in opposite direction, it is of motoring nature.
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
Interpoles provide mmf more than armature mmf in a dc machine.
- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
Interpoles provide mmf more than armature mmf in a dc machine.
a)
True
b)
False
|
|
Gaurav Chauhan answered |
Interpoles nullify armature cross magnetizing flux and the reactance voltage. So it is more than the armature mmf for a good efficient machine.
For a four pole, 16 slot armature with two coil-side/slot having wave connected progressive winding has single turn coils has simplex winding.The number of current paths- a)2
- b)6
- c)3
- d)4
Correct answer is option 'A'. Can you explain this answer?
For a four pole, 16 slot armature with two coil-side/slot having wave connected progressive winding has single turn coils has simplex winding.The number of current paths
a)
2
b)
6
c)
3
d)
4
|
|
Sakshi Tiwari answered |
The number of parallel path for a wave wound machine is equal to two.
If the speed of rotation for a four pole, 220V dc machine is 1 m/s, flux density as 2T having length of bore as 0.1m and radius of 0.5m.The emf induced under pole faces will be- a)0.2 V
- b)0.1 V
- c)0.2*pi V
- d)220 V
Correct answer is option 'A'. Can you explain this answer?
If the speed of rotation for a four pole, 220V dc machine is 1 m/s, flux density as 2T having length of bore as 0.1m and radius of 0.5m.The emf induced under pole faces will be
a)
0.2 V
b)
0.1 V
c)
0.2*pi V
d)
220 V
|
|
Partho Saha answered |
E = B*l*v
= 2*0.1*1
= 0.2 Volts.
= 2*0.1*1
= 0.2 Volts.
The effect of fringing increases as we- a)increase air gap
- b)decrease air gap
- c)increase in flux density
- d)introduce more ferric core material
Correct answer is option 'A'. Can you explain this answer?
The effect of fringing increases as we
a)
increase air gap
b)
decrease air gap
c)
increase in flux density
d)
introduce more ferric core material
|
|
Naveen Mukherjee answered |
Fringing is the effect in which the magnetic flux lines bulge out of the the flux. and it is introduced at the air gaps.
The effect of short pitched coil on the generated EMF is _____________- a)increasing
- b)decreasing
- c)either increasing or decreasing
- d)none of the mentioned
Correct answer is option 'B'. Can you explain this answer?
The effect of short pitched coil on the generated EMF is _____________
a)
increasing
b)
decreasing
c)
either increasing or decreasing
d)
none of the mentioned
|
|
Ashutosh Majumdar answered |
The effect of short pitched coil is to reduce the generated EMF and this reduction factor is cosε/2 and is referred to as coil pitch factor.
The brushes of a dc motor, are shifted by 5′, from the main field axis, then- a)demagnetizing or magnetizing effect may occur depending on machine
- b)cross-magnetization will be pronounced
- c)both cross-magnetization as well as magnetization and demagnetization will occur
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The brushes of a dc motor, are shifted by 5′, from the main field axis, then
a)
demagnetizing or magnetizing effect may occur depending on machine
b)
cross-magnetization will be pronounced
c)
both cross-magnetization as well as magnetization and demagnetization will occur
d)
none of the mentioned
|
|
Sakshi Tiwari answered |
When the brushes are shifted from GNA, there will either be magnetizing or demagnetizing effect will be observed.
Which of the following cannot reduce the terminal voltage of a dc shunt generator?- a)Commutation
- b)Armature reaction
- c)Armature ohmic losses
- d)Any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Which of the following cannot reduce the terminal voltage of a dc shunt generator?
a)
Commutation
b)
Armature reaction
c)
Armature ohmic losses
d)
Any of the mentioned
|
|
Rajeev Menon answered |
Commutation ideally does not reduce the terminal voltage of a dc machine. If it takes place properly at desired timings, the losses can be avoided. Armature reaction, ohmic losses contribute to the losses in the terminal voltage.
Ward-Leonard system of system of speed control is not recommended for- a)constant speed operation
- b)Wide speed
- c)frequent-motor reversed
- d)very slow speed
Correct answer is option 'A'. Can you explain this answer?
Ward-Leonard system of system of speed control is not recommended for
a)
constant speed operation
b)
Wide speed
c)
frequent-motor reversed
d)
very slow speed
|
|
Abhishek Chauhan answered |
Ward-Leonard system of system of speed control is not recommended for constant speed operation.
Most commercial compound dc generator are normally supplied by manufacturers as ______ compounded machines.- a)over
- b)under
- c)level
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Most commercial compound dc generator are normally supplied by manufacturers as ______ compounded machines.
a)
over
b)
under
c)
level
d)
none of the mentioned
|
|
Raghav Nambiar answered |
Most commercial compound dc generator are normally supplied by manufacturers as over compounded.
The method needed to limit cross-magnetizing effect is- a)by increasing reluctance of cross flux path
- b)by chamfering the pole faces
- c)by compensating winding
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The method needed to limit cross-magnetizing effect is
a)
by increasing reluctance of cross flux path
b)
by chamfering the pole faces
c)
by compensating winding
d)
any of the mentioned
|
Pankaj Mehta answered |
By ultimately increasing the reluctance of the magnetic circuit at the pole tips so that the armature reaction effect is neutralized.
In a short pitched coil, the coil pitch factor kp, is given by ____________- a)kp = cosε
- b)kp = cosε/2
- c)kp = √2πfrNΦcosε
- d)kp = cosε/2cosωrt
Correct answer is option 'B'. Can you explain this answer?
In a short pitched coil, the coil pitch factor kp, is given by ____________
a)
kp = cosε
b)
kp = cosε/2
c)
kp = √2πfrNΦcosε
d)
kp = cosε/2cosωrt
|
|
Ritika Mukherjee answered |
The effect of short pitched coil is to reduce the generated EMF, and this reduction factor is cosε/2, and is referred to as coil pitch factor.
For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.- a)2.788
- b)3.038
- c)2.688
- d)2.588
Correct answer is option 'A'. Can you explain this answer?
For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.
a)
2.788
b)
3.038
c)
2.688
d)
2.588
|
|
Rajeev Sharma answered |
Full load current = 7460/(200*0.85) = 43.88 A
Starting current = 1.5*43.88 = 65.883 A
R = V/I = 200/65.883
= 3.038 ohms
Starting resistance = 3.038 – 0.25 = 2.788 ohms.
A dc shunt motor is connected to the source through 3-point starter. If the field id kept open and starter handle is moved from off to on position, then- a)motor will not start
- b)armature will draw large current from source
- c)no sparking would occur
- d)all of the mentioned
Correct answer is option 'D'. Can you explain this answer?
A dc shunt motor is connected to the source through 3-point starter. If the field id kept open and starter handle is moved from off to on position, then
a)
motor will not start
b)
armature will draw large current from source
c)
no sparking would occur
d)
all of the mentioned
|
|
Ashutosh Majumdar answered |
Leaving the field winding open, the machine will not start as the exciting flux is zero.
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.
In an alternator, frequency per revolution is equal to- a)number of poles
- b)twice the number of poles
- c)speed in rps
- d)number of pole-pairs
Correct answer is option 'D'. Can you explain this answer?
In an alternator, frequency per revolution is equal to
a)
number of poles
b)
twice the number of poles
c)
speed in rps
d)
number of pole-pairs
|
Sakshi Roy answered |
For a P-pole machine, in n rev/sec, P/2n cycles/second are generated and cycles per second is referred to as frequency f of the EMF wave. Here in this question n=1
⇒ frequency per revolution = P/2
⇒ number of pole pairs.
⇒ frequency per revolution = P/2
⇒ number of pole pairs.
Mark the correct option which affects the terminal voltage of a dc shunt motor.- a)Armature reaction
- b)Source voltage variations
- c)Compensating winding
- d)Any of the mentioned
Correct answer is option 'C'. Can you explain this answer?
Mark the correct option which affects the terminal voltage of a dc shunt motor.
a)
Armature reaction
b)
Source voltage variations
c)
Compensating winding
d)
Any of the mentioned
|
|
Kiran Iyer answered |
The correct option that affects the terminal voltage of a DC shunt motor is c) Compensating winding.
A DC shunt motor consists of a field winding connected in parallel with the armature winding. The field winding is connected to a constant source of voltage, typically a DC power supply. The armature winding is connected to the load and produces the mechanical power output.
The terminal voltage of a DC shunt motor is the voltage measured across the armature terminals. It is influenced by various factors, and one of these factors is the compensating winding.
1. **Armature reaction:** Armature reaction is the magnetic field produced by the armature current that interacts with the field flux produced by the field winding. This interaction leads to a distortion of the field flux and can affect the terminal voltage of the motor. However, armature reaction does not directly affect the terminal voltage.
2. **Source voltage variations:** Variations in the source voltage can affect the terminal voltage of the motor. If the source voltage decreases, the terminal voltage will also decrease, and vice versa. However, source voltage variations are not the correct option in this scenario.
3. **Compensating winding:** A compensating winding is an additional winding connected in series with the armature winding. It is wound in the opposite direction to the armature winding and is placed in the pole shoes of the motor. The purpose of the compensating winding is to counteract the armature reaction and maintain a more stable field flux. By counteracting the armature reaction, the compensating winding helps to regulate the terminal voltage of the motor. When the armature reaction causes a drop in voltage, the compensating winding produces a voltage in the opposite direction to compensate for the drop. Conversely, when the armature reaction causes an increase in voltage, the compensating winding produces a voltage in the same direction to limit the increase. Thus, the compensating winding plays a crucial role in maintaining a stable terminal voltage in a DC shunt motor.
Therefore, the correct option that affects the terminal voltage of a DC shunt motor is c) Compensating winding.
A DC shunt motor consists of a field winding connected in parallel with the armature winding. The field winding is connected to a constant source of voltage, typically a DC power supply. The armature winding is connected to the load and produces the mechanical power output.
The terminal voltage of a DC shunt motor is the voltage measured across the armature terminals. It is influenced by various factors, and one of these factors is the compensating winding.
1. **Armature reaction:** Armature reaction is the magnetic field produced by the armature current that interacts with the field flux produced by the field winding. This interaction leads to a distortion of the field flux and can affect the terminal voltage of the motor. However, armature reaction does not directly affect the terminal voltage.
2. **Source voltage variations:** Variations in the source voltage can affect the terminal voltage of the motor. If the source voltage decreases, the terminal voltage will also decrease, and vice versa. However, source voltage variations are not the correct option in this scenario.
3. **Compensating winding:** A compensating winding is an additional winding connected in series with the armature winding. It is wound in the opposite direction to the armature winding and is placed in the pole shoes of the motor. The purpose of the compensating winding is to counteract the armature reaction and maintain a more stable field flux. By counteracting the armature reaction, the compensating winding helps to regulate the terminal voltage of the motor. When the armature reaction causes a drop in voltage, the compensating winding produces a voltage in the opposite direction to compensate for the drop. Conversely, when the armature reaction causes an increase in voltage, the compensating winding produces a voltage in the same direction to limit the increase. Thus, the compensating winding plays a crucial role in maintaining a stable terminal voltage in a DC shunt motor.
Therefore, the correct option that affects the terminal voltage of a DC shunt motor is c) Compensating winding.
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 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 induced emf in the armature of a 4-pole dc machine is- a)directly proportional to speed and field strength applied to it
- b)directly proportional to speed
- c)directly proportional to field strength applied to it
- d)inversely proportional to speed and inversely proportional to field strength applied to it
Correct answer is option 'A'. Can you explain this answer?
The induced emf in the armature of a 4-pole dc machine is
a)
directly proportional to speed and field strength applied to it
b)
directly proportional to speed
c)
directly proportional to field strength applied to it
d)
inversely proportional to speed and inversely proportional to field strength applied to it
|
|
Sanskriti Kaur answered |
Emf is proportional to speed of rotation and flux.
For a given dc generator, the external characteristic is plotted . Without using further plots, how can we obtain internal characteristic?
- a)By adding the IaRa drop to the plot
- b)By adding armature reaction
- c)By reducing IaRa drop
- d)All of the mentioned
Correct answer is option 'A'. Can you explain this answer?
For a given dc generator, the external characteristic is plotted . Without using further plots, how can we obtain internal characteristic?
a)
By adding the IaRa drop to the plot
b)
By adding armature reaction
c)
By reducing IaRa drop
d)
All of the mentioned
|
|
Prasad Verma answered |
To obtain the internal characteristic, you can:
- Add the IaRa drop to the plot
- Subtract from E0 the values of voltage drops due to armature reaction for different loads
- At large armature current, field current increases sharply to compensate for the voltage drop caused by armature reaction
The quantity which make rotating amplifier applicable in large power levels is/are- a)high power gain and favourable transient conditions
- b)favourable transient conditions
- c)high power gain
- d)favourable steady state conditions
Correct answer is option 'A'. Can you explain this answer?
The quantity which make rotating amplifier applicable in large power levels is/are
a)
high power gain and favourable transient conditions
b)
favourable transient conditions
c)
high power gain
d)
favourable steady state conditions
|
Manoj Chaudhary answered |
High Power Gain and Favorable Transient Conditions
The key factor that makes rotating amplifiers applicable in large power levels is the combination of high power gain and favorable transient conditions. Let's break down why this is the case:
High Power Gain:
- Rotating amplifiers are known for their ability to provide high power gain, which allows them to efficiently amplify signals to large power levels. This high power gain is crucial in applications where large power levels are required, such as in industrial settings or power systems.
Favorable Transient Conditions:
- In addition to high power gain, rotating amplifiers also offer favorable transient conditions. This means that they are able to handle sudden changes in input signals or load conditions without significant distortion or instability. This is important in applications where rapid changes in power levels occur, as rotating amplifiers can adapt quickly and maintain stability.
By combining high power gain with favorable transient conditions, rotating amplifiers become a reliable and efficient choice for large power level applications. Their ability to amplify signals effectively and handle dynamic changes in conditions makes them well-suited for demanding power systems and industrial settings.
Metadyne is _________ feedback with respect to main ___________- a)negative, current
- b)negative, voltage
- c)positive, current
- d)positive, voltage
Correct answer is option 'A'. Can you explain this answer?
Metadyne is _________ feedback with respect to main ___________
a)
negative, current
b)
negative, voltage
c)
positive, current
d)
positive, voltage
|
|
Lakshmi Desai answered |
Metadyne is negative feedback with respect to main current flowing in the second stage set of motors.
In an AC machine, the effect of distributing the turns in different slots, results in a further reduction of generated EMF by the factor kd. This factor is called ____________- a)distribution/speed factor
- b)coil pitch factor
- c)winding factor
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
In an AC machine, the effect of distributing the turns in different slots, results in a further reduction of generated EMF by the factor kd. This factor is called ____________
a)
distribution/speed factor
b)
coil pitch factor
c)
winding factor
d)
any of the mentioned
|
|
Alok Roy answered |
Introduction:
In an AC machine, the distribution of turns in different slots plays a crucial role in determining the generated electromotive force (EMF). The arrangement of turns in the slots affects the flux distribution and the resulting EMF. This effect is quantified by a factor called the distribution/speed factor (kd).
Explanation:
1. Distribution/Speed Factor:
The distribution/speed factor (kd) is a measure of the effect of distributing the turns in different slots of an AC machine. It represents the reduction in the generated EMF due to this distribution.
2. Flux Distribution:
When the turns are distributed in different slots, the flux produced by each turn is not uniform across the machine. The distribution of turns affects the magnetic field distribution and hence the flux distribution. This non-uniform flux distribution leads to a reduction in the generated EMF.
3. Effect on EMF:
The distribution of turns in different slots results in variations in the flux linkage with the armature conductors. Due to these variations, the EMF generated in each coil is not the same. This leads to a reduction in the overall generated EMF of the machine.
4. Calculation of Distribution/Speed Factor:
The distribution/speed factor (kd) is given by the formula kd = √(1 - s/sd), where s is the slot pitch and sd is the coil pitch. The slot pitch is the distance between the centers of two adjacent slots, and the coil pitch is the distance between the centers of two adjacent coils.
5. Significance of Distribution/Speed Factor:
The distribution/speed factor (kd) is an important parameter in the design and analysis of AC machines. It helps in determining the effect of distributing the turns in different slots on the generated EMF. By considering the distribution/ speed factor, engineers can optimize the coil and slot arrangements to achieve the desired EMF characteristics.
Conclusion:
In an AC machine, the distribution of turns in different slots has a significant impact on the generated EMF. The distribution/speed factor (kd) quantifies this effect and represents the reduction in the generated EMF due to the distribution of turns. By considering the distribution/speed factor, engineers can optimize the machine design to achieve the desired EMF performance.
In an AC machine, the distribution of turns in different slots plays a crucial role in determining the generated electromotive force (EMF). The arrangement of turns in the slots affects the flux distribution and the resulting EMF. This effect is quantified by a factor called the distribution/speed factor (kd).
Explanation:
1. Distribution/Speed Factor:
The distribution/speed factor (kd) is a measure of the effect of distributing the turns in different slots of an AC machine. It represents the reduction in the generated EMF due to this distribution.
2. Flux Distribution:
When the turns are distributed in different slots, the flux produced by each turn is not uniform across the machine. The distribution of turns affects the magnetic field distribution and hence the flux distribution. This non-uniform flux distribution leads to a reduction in the generated EMF.
3. Effect on EMF:
The distribution of turns in different slots results in variations in the flux linkage with the armature conductors. Due to these variations, the EMF generated in each coil is not the same. This leads to a reduction in the overall generated EMF of the machine.
4. Calculation of Distribution/Speed Factor:
The distribution/speed factor (kd) is given by the formula kd = √(1 - s/sd), where s is the slot pitch and sd is the coil pitch. The slot pitch is the distance between the centers of two adjacent slots, and the coil pitch is the distance between the centers of two adjacent coils.
5. Significance of Distribution/Speed Factor:
The distribution/speed factor (kd) is an important parameter in the design and analysis of AC machines. It helps in determining the effect of distributing the turns in different slots on the generated EMF. By considering the distribution/ speed factor, engineers can optimize the coil and slot arrangements to achieve the desired EMF characteristics.
Conclusion:
In an AC machine, the distribution of turns in different slots has a significant impact on the generated EMF. The distribution/speed factor (kd) quantifies this effect and represents the reduction in the generated EMF due to the distribution of turns. By considering the distribution/speed factor, engineers can optimize the machine design to achieve the desired EMF performance.
The air gap line represents- a)magnetic behaviour of the air gap of the dc machine
- b)magnetic behaviour of the air gap of the induction machine
- c)magnetic behaviour of the iron core
- d)all of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The air gap line represents
a)
magnetic behaviour of the air gap of the dc machine
b)
magnetic behaviour of the air gap of the induction machine
c)
magnetic behaviour of the iron core
d)
all of the mentioned
|
|
Snehal Rane answered |
Air gap line in the magnetization curve represents the ideal nature of the machine considering no saturation for the dc machine.
The main concern before doing hopkinson’s test for finding efficiency is- a)needs one motor and one generator is that it
- b)ignores iron and stray losses
- c)needs one motor
- d)requires identical shunt machines
Correct answer is option 'D'. Can you explain this answer?
The main concern before doing hopkinson’s test for finding efficiency is
a)
needs one motor and one generator is that it
b)
ignores iron and stray losses
c)
needs one motor
d)
requires identical shunt machines
|
|
Samridhi Bose answered |
It is must that both the machines are identical as required by the calculations.
The shunt motor starters that can be used is/are- a)3-point and 4-point starter
- b)5-point starter
- c)4-point starter
- d)5-point and 3-point starter
Correct answer is option 'A'. Can you explain this answer?
The shunt motor starters that can be used is/are
a)
3-point and 4-point starter
b)
5-point starter
c)
4-point starter
d)
5-point and 3-point starter
|
|
Aditya Deshmukh answered |
Both 4 point and 3 point starters are almost similar and are also used for the similar purpose i.e. for limiting the starting current and protecting the DC shunt wound and DC compound wound motors.
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.
Run-away for large DC machine is avoided by using- a)a turn or two of cumulative compounding
- b)compensating winding
- c)stablizer winding
- d)any of the mentioned
Correct answer is option 'B'. Can you explain this answer?
Run-away for large DC machine is avoided by using
a)
a turn or two of cumulative compounding
b)
compensating winding
c)
stablizer winding
d)
any of the mentioned
|
|
Debanshi Iyer answered |
The runaway in large machine is avoided by using compensating winding.
PMMDC offers ______ characteristics.- a)shunt
- b)series
- c)armature
- d)cumulative
Correct answer is option 'A'. Can you explain this answer?
PMMDC offers ______ characteristics.
a)
shunt
b)
series
c)
armature
d)
cumulative
|
|
Jyoti Basak answered |
As the field remains constant due to the constant field, it has shunt characteristic.
Chapter doubts & questions for DC Machines - 6 Months Preparation for GATE Electrical 2025 is part of Electrical Engineering (EE) exam preparation. The chapters have been prepared according to the Electrical Engineering (EE) exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Electrical Engineering (EE) 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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