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Which of the following methods of speed control of D.C. machine will offer minimum efficiency?
- a)Voltage control method
- b)Field control method
- c)Armature control method
- d)All of the above method
Correct answer is option 'C'. Can you explain this answer?
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Most Upvoted Answer
Which of the following methods of speed control of D.C. machine will o...
Armature Control Method
The armature control method is a method of speed control of a DC machine in which the voltage applied to the armature is varied by means of a variable resistance in series with it. This method is used when a wide range of speed control is required with a constant-torque load. However, this method offers minimum efficiency due to the following reasons:
Increased I2R losses
When the armature voltage is reduced, the current through the armature increases, resulting in an increase in I2R losses in the armature. These losses reduce the efficiency of the machine.
Reduced back EMF
The back EMF of a DC machine is directly proportional to the speed of the machine. When the armature voltage is reduced to decrease the speed, the back EMF also decreases. This results in a reduction in the overall efficiency of the machine.
Increased copper losses
The copper losses in the armature of a DC machine are directly proportional to the square of the current flowing through it. When the current through the armature is increased due to a decrease in the armature voltage, the copper losses also increase, reducing the efficiency of the machine.
Conclusion
Thus, the armature control method offers minimum efficiency due to the increased I2R losses, reduced back EMF, and increased copper losses. The other methods of speed control, such as the field control method and the voltage control method, are more efficient as they do not result in such losses.
The armature control method is a method of speed control of a DC machine in which the voltage applied to the armature is varied by means of a variable resistance in series with it. This method is used when a wide range of speed control is required with a constant-torque load. However, this method offers minimum efficiency due to the following reasons:
Increased I2R losses
When the armature voltage is reduced, the current through the armature increases, resulting in an increase in I2R losses in the armature. These losses reduce the efficiency of the machine.
Reduced back EMF
The back EMF of a DC machine is directly proportional to the speed of the machine. When the armature voltage is reduced to decrease the speed, the back EMF also decreases. This results in a reduction in the overall efficiency of the machine.
Increased copper losses
The copper losses in the armature of a DC machine are directly proportional to the square of the current flowing through it. When the current through the armature is increased due to a decrease in the armature voltage, the copper losses also increase, reducing the efficiency of the machine.
Conclusion
Thus, the armature control method offers minimum efficiency due to the increased I2R losses, reduced back EMF, and increased copper losses. The other methods of speed control, such as the field control method and the voltage control method, are more efficient as they do not result in such losses.
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Which of the following methods of speed control of D.C. machine will o...
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Which of the following methods of speed control of D.C. machine will offer minimum efficiency?a)Voltage control methodb)Field control methodc)Armature control methodd)All of the above methodCorrect answer is option 'C'. Can you explain this answer?
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