Power Electronics problems
- 1. The number of gates in an SCR is
Options- A. 1
- B. 3
- C. 4
- D. 6 Discuss
Correct Answer: 1
- 2. Assertion (A): A high dv/dt may cause triggering of a thyristor.
Reason (R): A high dv/dt results in charging current in the thyristor.
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:
The charging current may cause triggering.
- 3. A thyristor has maximum allowable junction temperature of 110° C and the ambient temperature is 40°C, If the maximum internal power dissipation is 50 W, the thermal resistance is
Options- A. 2° C/W
- B. 1.4° C/W
- C. 0.7°C/W
- D. 2.2° C/W Discuss
Correct Answer: 1.4° C/W
Explanation:
.
- 4. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
Options- A. about 1350 rpm
- B. about 720 rpm
- C. about 360 rpm
- D. either (b) or (c) Discuss
Correct Answer: about 720 rpm
Explanation:
In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.
- 5. To protect an SCR against high di/dt we connect
Options- A. a capacitance in series with SCR
- B. a capacitance in parallel with SCR
- C. an inductance in parallel with SCR
- D. an inductance in series with SCR Discuss
Correct Answer: an inductance in series with SCR
Explanation:
current through inductance cannot change instantaneously.
- 6. A single phase half wave regulator uses
Options- A. 2 diodes and 2 thyristors
- B. 2 thyristors
- C. 1 diode and 1 thyristor
- D. 2 diodes Discuss
Correct Answer: 1 diode and 1 thyristor
Explanation:
Regulation is possible only in positive half cycle.
- 7. A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20°C. If thermal resistance is 1.6° C/W, the junction temperature is
Options- A. 114°C
- B. 164°C
- C. 94° C
- D. 84° C Discuss
Correct Answer: 84° C
Explanation:
.
- 8. In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is
Options- A. 30°
- B. 60°
- C. 90°
- D. 120° Discuss
Correct Answer: 90°
Explanation:
Vdc ? (1 + cos a). Maximum possible output voltage occurs when a = 0.
- 9. A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ?t. The thyristor will conduct
Options- A. from 0 to 180°
- B. when v > 50 V
- C. from 0 to 90°
- D. When v < 50 V Discuss
Correct Answer: when v > 50 V
Explanation:
Thyristor can conduct only when it is forward biased. This occurs only when v > 50 V.
- 10. Assertion (A): A GTO circuit is more compact than SCR circuit
Reason (R): A GTO can be turned off by negative gate pulse.
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:
Since commutation circuit is not required, GTO circuit is compact.
More in Electronics and Communication Engineering:
Programming
Copyright ©CuriousTab. All rights reserved.