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  • Question

  • Which of these commutation methods uses an auxiliary SCR?


  • Options
  • A. Class A
  • B. Class B
  • C. Class C
  • D. Class D

  • Correct Answer
  • Class C 

    Explanation
    Class C commutation uses an auxiliary SCR and it is also called auxiliary commutation.
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    Power Electronics problems

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    • 1. In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time.

    • Options
    • A. True
    • B. False
      • Discuss
    • 2. If ton and toff are the turn on and turn off times of a thyristor, then

    • Options
    • A. ton and toff are almost equal
    • B. ton >> toff
    • C. toff >> ton
    • D. ton is about twice toff
      • Discuss
    • 3. In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be

    • Options
    • A. 30 A
    • B. 152 A
    • C. 15 A
    • D.
      • Discuss
    • 4. A dc circuit breaker must use

    • Options
    • A. natural commutation
    • B. forced commutation
    • C. both natural and forced commutation
    • D. either natural or forced commutation
      • Discuss
    • 5. The number of doped regions in a SCR is

    • Options
    • A. 2
    • B. 3
    • C. 4
    • D. 5
      • Discuss
    • 6. In an SCR, the anode current is controlled by

    • Options
    • A. gate current only
    • B. external circuit only
    • C. both gate current and external circuit
    • D. none of the above
      • Discuss
    • 7. A single phase half wave controlled rectifier circuit has an R-L load. A freewheeling diode is also in the circuit. When freewheeling diode is conducting the SCR

    • Options
    • A. is forward biased
    • B. is reverse biased
    • C. may be forward biased or reverse biased
    • D. forward biased initially but reverse biased afterwards
      • Discuss
    • 8. A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is

    • Options
    • A. a
    • B. 2 a
    • C. 4 a
    • D. 0.5 a
      • Discuss
    • 9. A DIAC has two terminals, anode and cathode.

    • Options
    • A. True
    • B. False
      • Discuss
    • 10. The rated current of a thyristor is 40 A. The holding current will be about :

    • Options
    • A. 20 A
    • B. 1 A
    • C. 100 mA
    • D. 10 mA
      • Discuss

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