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EC-604 (C) · POWER ELECTRONICS/Unsolved PYQ Paper

EC-604 (C) Power Electronics - May 2024 Question Paper

  1. Unit 1
    7 Marks
    aDescribe LASCR. Give its industrial applications. With neat circuit diagram explain how UJT firing circuit will generate pulse for an SCR.
  2. Unit 1
    7 Marks
    bWhat are "dv/dt" and "di/dt" ratings of SCRs? What happens if these ratings are exceeded?
  3. Unit 1
    7 Marks
    aSCRs with a rating of $1000\,\text{V}$ and $200\,\text{A}$ are available to be used in a string to handle $6\,\text{kV}$ and $1\,\text{kA}$. Calculate the number of series and parallel units required. Assume the derating factor is $0.1$.
  4. Unit 2
    7 Marks
    bExplain the working of three phase full converter for a firing angle of $45^{\circ}$.
  5. Unit 2
    7 Marks
    aA single phase full converter bridge is connected to RLE load. The supply voltage is $230\,\text{V}$, $50\,\text{Hz}$. The average load current of $10\,\text{A}$ is constant over the working range. For R = $0.4\,\Omega$ and L = $2\,\text{mH}$, compute the firing angle delay for E = $120\,\text{V}$.
  6. Unit 2
    7 Marks
    bDescribe how a freewheeling diode improves power factor in a converter system.
  7. Unit 3
    7 Marks
    aWhat is an inverter? List a few industrial applications of inverter.
  8. Unit 3
    7 Marks
    bDraw and explain the operation of three-phase series-inverter circuit.
  9. Unit 3
    7 Marks
    aExplain in detail about $180^{\circ}$ Conduction Mode of 3-\(\Phi\) Voltage Source Inverters.
  10. Unit 3
    7 Marks
    bA square-wave inverter has a dc source of $125\,\text{V}$, an output frequency of $60\,\text{Hz}$ and an RL series load with $R = 20\,\Omega$ and $L = 25\,\text{mH}$. Determine i) an expression for load current ii) rms load current iii) average source current
  11. Unit 4
    7 Marks
    aExplain the operation of step-up chopper with a neat circuit diagram and necessary output waveforms and also derive expression for output voltage.
  12. Unit 4
    7 Marks
    bThe step-down dc chopper has a resistive load, R = $20\,\Omega$ and input voltage, $V_s = 220\,\text{V}$. When the chopper remains on, its voltage drop, $V_{on} = 1.5\,\text{V}$ and chopping frequency, $f = 10\,\text{kHz}$. If the duty cycle is $80\%$. Estimate the: i) average output voltage ii) rms output voltage iii) Chopper efficiency
  13. Unit 4
    7 Marks
    aDescribe the Morgan chopper with associated voltage and current waveforms.
  14. Unit 5
    7 Marks
    bDescribe the operating principle of single-phase to single-phase step-up cyclo converter with the help of mid-point and bridge type configuration. Illustrate your answer with appropriate circuit and waveforms.
  15. Unit 1
    7 Marks
    aExplain the various modes of operation of TRIAC with the help of equivalent circuits and relevant waveforms.
  16. Unit 5
    7 Marks
    bA single phase half wave AC voltage controller has a resistive load of R = $40\,\Omega$ and the input voltage is $V_s = 230\,\text{V}$, $50\,\text{Hz}$. The Delay angle of thyristor is $50^{\circ}$. Determine i) The rms value of output voltage $V_0$ ii) The input power factor iii) The average input current
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