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ECE :: Power Electronics

  1. A dc circuit breaker must use

  2. A.
    natural commutation
    B.
    forced commutation
    C.
    both natural and forced commutation
    D.
    either natural or forced commutation

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  3. In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero.

  4. A.
    True
    B.
    False

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  5. An RC snubber circuit is used to protect a thyristor against :

  6. A.
    false triggering
    B.
    failure to turn on
    C.
    switching transients
    D.
    failure to commutate

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  7. A DIAC has two terminals, anode and cathode.

  8. A.
    True
    B.
    False

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  9. A single phase semiconverter has a freewheeling diode. If the firing angle is a and the load is purely resistive, the periods of conduction and freewheeling respectively are

  10. A.
    p - a and 0
    B.
    p - a and a
    C.
    p + a and 0
    D.
    p + a and a

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  11. A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be

  12. A.
    about 300 rpm
    B.
    about 150 rpm
    C.
    about 75 rpm
    D.
    about zero

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  13. A static induction thyristor

  14. A.
    is a majority carrier device
    B.
    is a minority carrier device
    C.
    either a majority carrier or minority carrier device
    D.
    has a total number of 2 leads

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  15. A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to

  16. A.
    one half wave of output
    B.
    one full wave of output
    C.
    two full waves of output
    D.
    either (b) or (c)

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  17. Which of these triggering methods for series connected SCRs use LASCR in the gate circuit?

  18. A.
    Resistance triggering
    B.
    Simultaneous triggering
    C.
    Sequential triggering
    D.
    Optical triggering

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  19. A 3 phase ac regulator uses

  20. A.
    3 thyristors
    B.
    6 thyristors
    C.
    9 thyristors
    D.
    12 thyristors

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