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ECE :: Power Electronics

Power Electronics - Section 1
Power Electronics - Section 2
Power Electronics - Section 3
Power Electronics - Section 4
Power Electronics - Section 5
Power Electronics - Section 6
Power Electronics - Section 7
Power Electronics - Section 8
Power Electronics - Section 9

  1. An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be

    2. A.
    50 A
    B.
    25 A
    C.
    less than 50 A but more than 25 A
    D.
    less than 25 A

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  2. The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes

    3. A.
    about 100 times
    B.
    about 10 times
    C.
    about 3 times
    D.
    about twice

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  3. In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is

    4. A.
    333.33
    B.
    250
    C.
    500
    D.
    1000

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  4. Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.

    5. A.
    True
    B.
    False

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  5. Assertion (A): Inverters and choppers use fast switching thyristors

    Reason (R): Fast switching SCR has low turn off time.

    6. 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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  6. The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by

    7. A.
    forward characteristics of thyristors
    B.
    reverse recovery characteristics of thyristors
    C.
    both forward and reverse recovery characteristics of thyristors
    D.
    none of the above

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  7. A chopper

    8. A.
    converts constant voltage dc into ac and then into variable voltage dc
    B.
    converts constant voltage dc into variable voltage dc directly
    C.
    converts ac of one frequency into ac of another frequency
    D.
    converts ac to dc

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  8. Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous

    Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.

    9. 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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  9. In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally

    10. A.
    equal
    B.
    different
    C.
    equal or different
    D.
    different but sometimes equal

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  10. An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is

    11. A.
    16% maximum
    B.
    40% of maximum
    C.
    60% of maximum
    D.
    84% of maximum

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