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- Question
Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin ?t and a1 = a2 are the firing angles of the two converters. If a1 = a2 = 0, the dc output voltage is
Options- A.
- B.
- C.
- D.
- Correct Answer
-
ExplanationOutput voltage is for each.
Power Electronics problems
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- 1. In integral cycle control the period of on-off control should be more than mechanical time constant of load.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
It should be less than mechanical time constant.- 2. Assertion (A): The gate current of an SCR is always in the form of pulses.
Reason (R): The gate losses, in pulse triggering, are low.
Options- 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 Discuss
Correct Answer: Both A and R are correct and R is correct explanation of A
Explanation:
Gate current in the form of pulses is commonly used because gate losses are low.- 3. A reactor is used in a dual converter operating in non-circulating current mode.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Reactor is used only for circulating current mode.- 4. Current chopping leads to
Options- A. over voltage
- B. over current
- C. both over voltage and over current
- D. either over voltage or over current Discuss
Correct Answer: over voltage
Explanation:
e = L
. In current chopping is high. Hence e is high.
- 5. A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is
Options- A. zero
- B. about 1 V
- C. same as input voltage
- D. twice the input voltage Discuss
Correct Answer: same as input voltage
Explanation:
Before triggering the whole of applied voltage is across SCR and load current is zero.- 6. In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be
Options- A. 400 V
- B. about 100 V
- C. about 20 V
- D. zero Discuss
Correct Answer: zero
Explanation:
In a three-phase full wave regulator, output voltage is zero if a ? 150°.- 7. 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
Options- A. p - a and 0
- B. p - a and a
- C. p + a and 0
- D. p + a and a Discuss
Correct Answer: p - a and 0
Explanation:
Freewheeling diode conducts only when load is inductive. If load is purely resistive free wheeling diode does not come into operation.- 8. A cycloconverter is
Options- A. ac-dc converter
- B. dc-ac converter
- C. dc-dc converter
- D. ac-ac converter Discuss
Correct Answer: ac-ac converter
Explanation:
It changes ac at frequency f into ac at a frequency different from f.- 9. During forward blocking state of SCR, the voltage and current respectively are
Options- A. high and high
- B. low and low
- C. high and low
- D. low and high Discuss
Correct Answer: high and low
Explanation:
Voltage is high but current is nearly zero.- 10. A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 ? per phase. The peak value of load current is
Options- A. 40 A
- B. 20 A
- C. 10 A
- D. 5 A Discuss
Correct Answer: 20 A
Explanation:
Two resistances are in series at any time.
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