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Power Electronics Part- 5 Objective Questions with Answers

Power Electronics Objective Questions with Answers: Part-5

1. SCR is the solid state equivalent of
(a) Transistor
(b) Thyratron
(c) Vacuum diode
(d) Crystal diode

Answer: B
2. With gate open, if the supply voltage exceeds the breakover voltage of SCR, then SCR will conduct
(a) False
(b) True
(c) For DC
(d) For AC

Answer: B
3. The SCR is turned off when the anode current falls below
(a) Forward current rating
(b) Break over voltage
(c) Holding current
(d) Latching current

Answer: C
4. In a SCR circuit, the angle of conduction can be changed by changing
(a) Anode voltage
(b) Anode current
(c) Forward current rating
(d) Gate current

Answer: D
5. The normal way to close a SCR is by appropriate
(a) Gate current
(b) Cathode current
(c) Anode current
(d) Forward current

Answer: A
6. An SCR has ......PN junctions
(a) Two
(b) Four
(c) Three
(d) One

Answer: C
7. If gate current is increased, the anode-cathode voltage at which SCR closes is.....
(a) Increased
(b) Decreased
(c) Maximum
(d) Least

Answer: B
8. A conducting SCR can be opened by reducing ..... to zero
(a) Supply voltage
(b) Grid voltage
(c) Grid current
(d) Anode current

Answer: A
9. With gate open, a SCR can be turned-on by making supply voltage....
(a) Minimum
(b).Reverse
(c) Equal to cathode voltage
(d) Equal to breakover voltage

Answer: D
10. If firing angle in a SCR rectifier is increased, output is....
(a) Increased
(b) Maximum
(c) Decreased
(d) Unaffected

Answer: C
11. A SCR is a ...switch
(a) Two directional
(b) Unidirectional
(c) Three directional
(d) Four directional

Answer: B
12. The anode of SCR is always maintained at........potential with respect to cathode
(a) Positive
(b) Zero
(c) negative
(d) Equipotential

Answer: A
13. IF the chopper switching frequency is 200Hz and Ton time is 2ms, the duty cycle is
(a) 0.4
(b) 0.8
(c) 0.6
(d) None of the above

Answer: A
14. Speed control of induction motor can be effected by varying
(a) Flux
(b) Voltage input to stator
(c) Keeping rotor coil open
(d) None of the above

Answer: B
15. In a Dc motor if the field coil gets opened, the speed of the motor will
(a) Decrease
(b) Come to stop
(c) Increase
(d) None of the above

Answer: C

 Solution Hint:
[11] SCR will conduct in one direction only. So it act as a unidirectional switch.
[13] T=1/f, D = TON/T
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