Power Electronics problems
- 1. In a series inverter
Options- A. the commutating elements carry full load current
- B. the commutating elements carry upto 50% of load current
- C. the commutating elements do not carry load current
- D. any of the above Discuss
Correct Answer: the commutating elements carry full load current
- 2. When a UJT is used as a relaxation oscillator the current should be
Options- A. less than Ip
- B. more than Iv
- C. more than Ip but less than Iv
- D. negative Discuss
Correct Answer: more than Ip but less than Iv
- 3. Two single phase semi-converters are connected in series to form a series converter. The input is v = Vm sin ?t and a1, a2 are the firing angles. If a1 = 0, the dc output voltage is
Options- A.
(1 + cos a2) - B. (2 + cos a2)
- C. (3 + cos a2)
- D. (4 + cos a2)
Discuss
Correct Answer:
(3 + cos a2) - 4. If we connect two silicon unilateral switches in anti- parallel we get
Options- A. SCR
- B. SBS
- C. SCS
- D. UJT Discuss
Correct Answer: SBS
- 5. When UJT is used for thyristor gate signal, the output of UJT is
Options- A. sine wave
- B. square wave
- C. saw tooth wave
- D. either (a) or (c) Discuss
Correct Answer: saw tooth wave
- 6. In a single phase full wave regulator feeding a resistive load, the average current over one full cycle
Options- A. is always zero
- B. cannot be zero
- C. may be sometimes zero
- D. is always positive Discuss
Correct Answer: is always zero
- 7. A UJT exhibits negative resistance characteristics when
Options- A. Current is less than valley current
- B. Current is less than peak current
- C. Current is more than peak current but less than valley current
- D. None of the above Discuss
Correct Answer: Current is more than peak current but less than valley current
- 8. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque
Options- A. will be less than 100 N-m
- B. will be more than 100 N-m
- C. may be more or less than 100 N-m depending on motor parameters
- D. very small Discuss
Correct Answer: will be more than 100 N-m
- 9. In a single phase semi-converter the number of thyristors is
Options- A. 16
- B. 8
- C. 4
- D. 2 Discuss
Correct Answer: 2
- 10. A NAND gate has 3 inputs and one output. The number of thyristors required for this gate are
Options- A. 1
- B. 2
- C. 3
- D. 3 or 4 Discuss
Correct Answer: 3
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