A single phase semiconverter has a freewheeling diode. If the firing angle is a

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Question
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

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.

Power Electronics problems

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1. 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

2. Two semiconverters are connected in series to form a single phase series converter. The input v = V_m 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.

3. In integral cycle control the period of on-off control should be more than mechanical time constant of load.
Options
A. True
B. False

4. 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

7. 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

8. 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

9. A single phase half wave controlled rectifier circuit is feeding on RL load. The circuit has a freewheeling diode. The input voltage is v = V_m sin ?t. If I₀ is the load current during the conduction of freewheeling diode, the KVL equation during the conduction of free wheeling diode is
Options
A.
B.
C.
D.

10. A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is
Options
A. 3
B. 4
C. 6
D. 10

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