power-electronics electronics-and-communication-engineering question and answers -Page 9

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Power Electronics problems

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

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 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

4. 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

6. 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

7. 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

8. 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.

9. 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

10. Which of these triggering methods for series connected SCRs use LASCR in the gate circuit?
Options
A. Resistance triggering
B. Simultaneous triggering
C. Sequential triggering
D. Optical triggering

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