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  • Question

  • A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be


  • Options
  • A. about 1350 rpm
  • B. about 720 rpm
  • C. about 360 rpm
  • D. either (b) or (c)

  • Correct Answer
  • about 720 rpm 

    Explanation
    In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.

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    • Options
    • A. True
    • B. False
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    • Options
    • A. True
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    • Options
    • A. do not require any supply
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    • Options
    • A. A, B, C, D, E, F, H
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    • A. A
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    • Options
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    • Options
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    • C. 5 x 10-3
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    • Options
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    • Options
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