mcq of cycloconverter

                                                                      

 1.Which of the following statements are correct for cyclo converters?

1. Step-down cyclo converter c works on natural commutation 2. Step-up cc requires forced commutation 3. Load commutated cc works online commutation

4.Load commutated cc requires a generated emf in the load circuit.

2, 3,4 1,2, 4 1,2 1,2, 3

Correct answers: 1,2, 4

2.A 3-phase to single-phase conversion device employs a 6-pulse bridge cyclo converter. For an input voltage of 200 V per phase, the fundamental RMS value of output voltage is

600√3/π V 300/π V 600/π V 300√3/π V Correct answers: 600√3/π V

3.Consider the following statements regarding cyclo converters: 1. In 1-phase to 1-phase CC, firing angle may be varied 2. In 3-phase to 1-phase CC, firing angle may be kept constant 3. In 1-phase to 1-phase CC, firing angle may be kept constant 4. In 3-phase to 1-phase CC, firing angle may be varied 5. In 3-phase to 1-phase CC, firing angle must be varied From these, the correct statements 2,3, 5 1, 3,5 2,4, 5 2, 3 4

Correct answers: 1, 3,5

4.In three-phase cyclo converters, the reduction factor is (input frequency/output frequency) -1 (input frequency/output frequency) -1/2 (input frequency/output frequency) 1/2 input frequency/output frequency

Correct answers: (input frequency/output frequency) -1

5.The single-phase bridge type cycloconverter uses __________ number of SCR none of the mentioned 4 6 8

Correct answers: 8

6.How many switches are used to build a three-phase to three-phase cyclo converter? 18 24 10 14 Correct answers: 18

7. A single-phase full controlled converter with RLE load will act like a line-commutated inverter when the firing angle α α > 90° α > 180° α < 90> 90°

α=90° correct answer is; α > 90°

8. In a 1-Φ full converter, the number of SCRs conducting during overlap is

1 3 4 2

Correct answers: 4

9.Calculate the value of the Crest factor if Vpeak=789 V and Vr.m.s=489 V. 1.61 1.26 1.63 1.54 Correct answers: 1.61

10.In a B-2 type full controlled bridge converter

four SCRs conduct at a time two SCRs conduct at a time one SCR conducts at a time three SCRs conduct at a time Correct answers: two SCRs conduct at a time

11.A single-phase uncontrolled-converter is a _________ quadrant converter uses 4 diodes 4 SCRs 4 SCRs and 2 diodes 4 SCRs and 2 diodes Correct answers: 4 diodes

12. In a single-phase semi converter, if output voltage has peak and average values of 400 and 200 V respectively, the firing angle is 55.15° 73.4° 80.9° 140.3° Correct answers: 55.15°

13.In a three-phase bridge rectifier, the maximum conduction of each thyristor is..... 90° 30° 120° 60° Correct answers: 120°

14.In a 1-Φ full converter, for continuous conduction, each pair of SCRs conduct for angle

π + α α π – α π

Correct answers: π

15.In a single-phase full converter if output voltage has peak and average values of 350 V and 150V respectively, then the firing angle is 50.0° 47.7° 140.8° 130.5° Correct answers: 47.7°

16.A single-phase fully controlled-converter is a _________ quadrant converter one none two, one & two Correct answers: two,

17.Applications of cyclo converters include static VAr compensation induction heating all of the mentioned speed control of ac drives

Correct answers: all of the mentioned