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  • Question

  • A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be


  • Options
  • A. 0.9
  • B. 0.8
  • C. 0.75
  • D. 0.6

  • Correct Answer
  • 0.75 

    • Power Electronics problems

    Search Results

    • 1. If 4 quadrant operation is required we need

    • Options
    • A. dual converter
    • B. full converter
    • C. semi converter
    • D. none of the above
      • Discuss
    • 2. In a step down chopper using time ratio control, the input voltage is V and duty cycle is a. The load is purely resistive having resistance R. The average and rms load currents are

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 3. In brushless excitation system of modern alternators, the main exciter is

    • Options
    • A. dc generator
    • B. ac generator
    • C. either dc or ac generator
    • D. induction generator
      • Discuss
    • 4. An n pulse rectifier is fed by a source having an inductance L. If load current is I0, the voltage drop due to overlap is

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 5. In the circuit of figure, the waveshape of load current when thyristor conducting is

    • Options
    • A. constant
    • B. increasing exponentially
    • C. decreasing exponentially
    • D. either (b) or (c)
      • Discuss
    • 6. In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage

    • Options
    • A. will have positive part only
    • B. will have both positive and negative parts
    • C. may have both positive and negative parts
    • D. will have negative part if load is inductive
      • Discuss
    • 7. As compared to BJT, MOSFET has

    • Options
    • A. lower switching losses and higher conduction losses
    • B. higher switching losses and higher conduction losses
    • C. higher switching losses and lower conduction losses
    • D. lower switching losses and lower conduction losses
      • Discuss
    • 8. In pulse width modulation of chopper

    • Options
    • A. T is kept constant and Ton is varied
    • B. Ton is kept constant T is varied
    • C. both T and Ton are varied
    • D. either T or Ton is varied
      • Discuss
    • 9. All other parameters remaining the same, a 3 phase bridge inverter with 180° mode of operation

    • Options
    • A. has the same peak thyristor current as in 120° mode of operation
    • B. has higher peak thyristor current than in 120° mode of operation
    • C. has lower peak thyristor current than in 120° mode of operation
    • D. any of the above
      • Discuss
    • 10. A class D chopper

    • Options
    • A. can operate in first quadrant only
    • B. can operate in second quadrant only
    • C. can operate in either first or fourth quadrant
    • D. can operate in all the quadrants
      • Discuss

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