All Free Electrical Engineering MCQs with Answers
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3,143 questions · page 138 of 158
- A. equal division of voltage across each thyristor
- B. equal division of current through each thyristor in parallel
- C. equal division of voltage across each thyristor in parallel
- D. equal division of current through each thyristor in series
Explanation: A dynamic equalizing circuit, typically an RC snubber, is connected across series thyristors to equalize transient voltage sharing during…
Correct answer: equal division of voltage across each thyristor- A. 60
- B. 70
- C. 80
- D. 90
Explanation: With a 0.1 derating factor, only 90% of the parallel string capacity is usable. Thus, n × 1 × 0.9 = 72, giving n = 80 SCRs.
Correct answer: 80- A. 76.3 %
- B. 91.6 %
- C. 83.3 %
- D. 90.9 %
Explanation: Each of the 6 parallel paths contains 10 series thyristors, giving rated capacity of 12 kV and 6 kA.
Correct answer: 76.3 %- A. 5, 7
- B. 4, 6
- C. 7, 5
- D. 6, 4
Explanation: The required series count is 11/(1.8 × 0.9) = 6.79, so 7 SCRs are needed in series.
Correct answer: 7, 5- A. R and C in series but with diode across C
- B. R and C in series but with diode across R
- C. Series R and diode with C across R
- D. Series R and diode with C across R
Explanation: A dynamic equalising network uses a series R-C circuit across each SCR, with a diode across the resistor.
Correct answer: R and C in series but with diode across R- A. String efficient
- B. Reliability factor
- C. Factor of safety
- D. Derating factor
Explanation: The derating factor indicates how far a thyristor string is operated below its ideal rated capacity, allowing for unequal sharing and…
Correct answer: Derating factor- A. series connection.
- B. parallel connection.
- C. anti parallel connection.
- D. both B and C.
Explanation: Parallel SCRs share the load current, so their combined current rating meets a high-current demand.
Correct answer: parallel connection.- A. To limit di / dt of SCR
- B. To limit dV / dt of SCR
- C. For voltage equalisation
- D. Both B and C
Explanation: The dynamic equalising circuit limits rapid voltage changes across an SCR and promotes equal transient voltage sharing among…
Correct answer: Both B and C- A. high current demand
- B. low voltage demand
- C. low current demand
- D. high voltage demand
Explanation: Series-connected SCRs add their voltage-blocking capabilities, making the arrangement suitable for high-voltage operation.
Correct answer: high voltage demand- A. 0 - 0.5 V.
- B. 0.5 - 1 V.
- C. 1 - 1.5 V.
- D. 1.5 - 2 V.
Explanation: A conducting SCR typically has an on-state voltage drop of about 1 to 1.5 V, caused by the forward-biased junctions and semiconductor…
Correct answer: 1 - 1.5 V.- A. IGBTs
- B. COOLMOS
- C. TRIAC
- D. SITS
Explanation: IGBTs, COOLMOS devices, and SITs are transistor-type power semiconductor devices.
Correct answer: TRIAC- A. SIT
- B. BJT
- C. TRIAC
- D. IGBT
Explanation: A SIT, or static induction transistor, is normally ON because its gate controls and can pinch off the conducting channel.
Correct answer: SIT- A. 3 - 10 µs
- B. 3 - 50 µs
- C. 3 - 100 µs
- D. 3 - 500 µs
Explanation: The typical turn-off time of a thyristor is commonly taken as approximately 3 to 100 microseconds, although the exact value depends on the…
Correct answer: 3 - 100 µs- A. B.JTs
- B. MOSFETs
- C. IGBTs
- D. All of above
Explanation: Power transistors include power BJTs, power MOSFETs, and IGBTs, each designed to handle substantial voltage and current.
Correct answer: All of above- A. charge carriers of J2 junction recombined
- B. charge carriers of J2 junction is swept out
- C. charge carrier of J1 junction removed
- D. charge carriers of J3 junction is removed
Explanation: During gate recovery, the remaining charge carriers around the central J2 junction recombine, restoring its blocking capability.
Correct answer: charge carriers of J2 junction recombined- A. charge carrier of junction J2 recombined
- B. charge carrier of junction J1 is swept out
- C. charge carrier of junction J3 is swept out
- D. both B and C
Explanation: During reverse recovery of an SCR, stored carriers are swept out from the outer junction regions J1 and J3, allowing reverse current to…
Correct answer: both B and C- A. SIT is a high power, high frequency device
- B. SIT is a high power, low frequency device
- C. SIT is a high power, high voltage device
- D. SIT is a low power, high frequency device
Explanation: A SIT combines high power-handling capability with high-frequency operation because its majority-carrier conduction avoids the long…
Correct answer: SIT is a high power, high frequency device- A. Delay time
- B. Spread time
- C. Rise time
- D. Same for every case
Explanation: Conduction spreading occurs during the spread time, when the conducting region expands through the thyristor junction area.
Correct answer: Spread time- A. Positive gate signal
- B. Positive drain signal
- C. Positive source signal
- D. None of these
Explanation: A GTO turns on with a positive gate current or voltage relative to its cathode, just like an SCR.
Correct answer: Positive gate signal- A. 10 - 20 µs
- B. 40 - 60 µs
- C. 1 - 4 µs
- D. 90 - 100 µs
Explanation: The typical SCR rise time is in the microsecond range, commonly about 1 to 4 μs.
Correct answer: 1 - 4 µs