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ECE :: Power Electronics

  1. In a dual converter both converters work as rectifiers.

  2. A.
    True
    B.
    False

  3. A single phase full wave regulator feeds R-L load. The best gating signal is

  4. A.
    short duration pulses
    B.
    long duration pulses
    C.
    pulse train
    D.
    either (a) or (b)

  5. A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if

  6. A.
    load torque is constant
    B.
    load torque increases with increase in speed
    C.
    load torque decreases with increase in speed
    D.
    either (a) or (b)

  7. A cycloconverter cannot give a frequency higher than input frequency.

  8. A.
    True
    B.
    False

  9. A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20°C. If thermal resistance is 1.6° C/W, the junction temperature is

  10. A.
    114°C
    B.
    164°C
    C.
    94° C
    D.
    84° C

  11. In a single phase dual converter, a1, and a2 are firing angles of the two converters. Then

  12. A.
    a1 - a2 =
    B.
    a1 + a2 = p
    C.
    a1 - a2 = p
    D.
    a1 + a2 =

  13. The number of gates in an SCR is

  14. A.
    1
    B.
    3
    C.
    4
    D.
    6

  15. The waveshape of output voltage of half bridge inverter is

  16. A.
    sinusoidal
    B.
    square
    C.
    triangular
    D.
    either (a) or (b)

  17. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be

  18. A.
    about 1350 rpm
    B.
    about 720 rpm
    C.
    about 360 rpm
    D.
    either (b) or (c)

  19. The gate current required to turn on an SCR is

  20. A.
    few amperes
    B.
    a few mA
    C.
    almost equal to anode current
    D.
    about 50% of anode current