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The speed of an induction motor is increased by increasing the frequency by 20%. If the magnetising current of the machine is to remain constant, then
  • a)
    slip must be increased by 20%
  • b)
    supply voltage must be increased by 20%
  • c)
    supply voltage must be decreased by 20%
  • d)
    supply voltage must be increased by 10%
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
The speed of an induction motor is increased by increasing the frequen...
Explanation:

Increasing the frequency:
When the frequency of the supply to an induction motor is increased by 20%, the speed of the motor will also increase by 20%. This is because the synchronous speed of the motor is directly proportional to the frequency of the power supply.

Constant magnetising current:
In order to keep the magnetising current of the motor constant, the supply voltage needs to be adjusted accordingly. The magnetising current is responsible for establishing the magnetic field in the motor, and keeping it constant ensures stable operation.

Supply voltage adjustment:
To compensate for the increase in frequency and maintain the magnetising current constant, the supply voltage must be increased by 20%. This adjustment ensures that the motor continues to operate efficiently and within its design parameters.
Therefore, the correct answer is option B) supply voltage must be increased by 20%. This adjustment will allow the motor to run at the increased speed without affecting its performance or efficiency.
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Community Answer
The speed of an induction motor is increased by increasing the frequen...
Voltage of 3 - ϕ induction motor is given by
V = 4.44 ϕ f N
N remains constant for the same motor, then
also ϕ ∝ Im
Where ϕ = Air gap flux in Weber
V = Terminal voltage in volt
N = Number of turns
f = Supply frequency in Hz
Im =  Magnetising current
So that to keep air gap flux constant, voltage and frequency must be increased and decreased in the same proportion.
Solution:
For magnetising current to remain constant, we need to maintain the V/f ratio constant.
Given that the supply frequency is increased by 20%.
Hence the supply voltage must be increased by 20%
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The speed of an induction motor is increased by increasing the frequency by 20%. If the magnetising current of the machine is to remain constant, thena)slip must be increased by 20%b)supply voltage must be increased by 20%c)supply voltage must be decreased by 20%d)supply voltage must be increased by 10%Correct answer is option 'B'. Can you explain this answer?
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