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Power Electronics problems

  • 1. In the circuit of figure, the waveshape of load current when thyristor conducting is
    Electronics and Communication Engineering Power Electronics: 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
  • 2. 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
  • 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. 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
  • 5. If 4 quadrant operation is required we need

  • Options
  • A. dual converter
  • B. full converter
  • C. semi converter
  • D. none of the above
    • Discuss
  • 6. 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
    • Discuss
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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

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