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ECE :: Power Electronics

  1. In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is

  2. A.
    30°
    B.
    60°
    C.
    90°
    D.
    120°

  3. A high frequency series inverter consists of

  4. A.
    a number of series inverters in series
    B.
    a number of series inverters in parallel
    C.
    a number of parallel inverters in parallel
    D.
    a number of parallel inverters in series

  5. In an SCR, the anode current consists of

  6. A.
    only holes
    B.
    only electrons
    C.
    both electrons and holes
    D.
    either electrons or holes

  7. In the below figure, the average value of load current is 15 A. The load is highly inductive. The peak value of thyristor current is

  8. A.
    15 A
    B.
    152 A
    C.
    D.
    30 A

  9. A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load

  10. A.
    rectification efficiency will be more than 0.6 and TUF will be more than 0.35
    B.
    rectification efficiency will be more than 0.6 but TUF will be less than 0.35
    C.
    rectification efficiency will be less than 0.6 and TUF will be less than 0.35
    D.
    rectification efficiency will be less than 0.6 but TUF will be more than 0.35

  11. Assertion (A): A high dv/dt may cause triggering of a thyristor.

    Reason (R): A high dv/dt results in charging current in the thyristor.

  12. 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

  13. Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V.

    Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

  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

  15. When the core of a saturable reactor is saturated, the inductance is high.

  16. A.
    True
    B.
    False

  17. In controlled heating circuits, thyristors act as

  18. A.
    rectifier
    B.
    inverter
    C.
    ac regulator
    D.
    chopper

  19. In a fully controlled bridge converter feeding a resistive load the waveshapes of output voltage and output current

  20. A.
    are always similar
    B.
    can never be similar
    C.
    may be similar or dissimilar
    D.
    are similar only if a = 0