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ECE :: Power Electronics

  1. A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct

  2. A.
    from 0 to 180°
    B.
    when v > 50 V
    C.
    from 0 to 90°
    D.
    When v < 50 V

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  3. The symbol in figure is for

  4. A.
    DIAC
    B.
    P-N junction diode
    C.
    Schottky diode
    D.
    None of the above

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  5. In a 3 phase semiconverter, the firing frequency is

  6. A.
    equal to line frequency
    B.
    3 times the line frequency
    C.
    6 times the line frequency
    D.
    12 times the line frequency

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  7. Present day HVDC converters are all

  8. A.
    3 pulse converters
    B.
    6 pulse converters
    C.
    12 pulse converters
    D.
    either 6 pulse or 12 converters

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  9. A single phase full converter gives maximum and minimum output voltage at firing angles of

  10. A.
    0 and 180° respectively
    B.
    180° and 0° respectively
    C.
    0 and 90° respectively
    D.
    90° and 0° respectively

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  11. A thyristor has its gate current zero. To start conduction the forward voltage must exceed

  12. A.
    about 0.5 V
    B.
    forward breakover voltage
    C.
    on state voltage
    D.
    peak working off state forward voltage

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  13. Assertion (A): Snubber circuit has an RC series circuit in parallel with SCR

    Reason (R): Voltage across a capacitor can not change instantaneously.

  14. A.
    Both A and R are correct and R is correct explanation of A
    B.
    Both A and R correct but R is not correct explanation of A
    C.
    A is correct but R is wrong
    D.
    A is wrong but R is correct

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  15. In dielectric heating, the thyristor circuits consist of

  16. A.
    rectifier-chopper combination
    B.
    controlled rectifier
    C.
    ac regulator
    D.
    rectifier-inverter combination

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  17. On load tap changer using thyristors can have a maximum of two taps.

  18. A.
    True
    B.
    False

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  19. Assertion (A): A cycloconverter may be line commutated or forced commutated

    Reason (R): A step up cycloconverter requires forced commutation.

  20. A.
    Both A and R are correct and R is correct explanation of A
    B.
    Both A and R correct but R is not correct explanation of A
    C.
    A is correct but R is wrong
    D.
    A is wrong but R is correct

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