Electronics and Communication Engineering - Power Electronics

46. 

If Vdc1 is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and Vdc2 is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then

A. Vdc1 = 0.5 Vdc2 for all values of firing angle
B. Vdc1 = Vdc2 for all values of firing angle
C. Vdc1 ≤ 0.5 Vdc2 for all values of firing angle
D. Vdc1 ≥ 0.5 Vdc2 for all values of firing angle

Answer: Option A

Explanation:

and Vdc = (1 + cos a).


47. 

A semi converter operates in two quadrants.

A. True
B. False

Answer: Option B

Explanation:

It operates only in quadrant.


48. 

Figure shows a chopper feeding RLE load, The free wheeling diode conducts when

A. thyristor is on
B. thyristor is off
C. both when thyristor is on and thyristor is off
D. partly when thyristor is off and partly when thyristor is on

Answer: Option B

Explanation:

FD is forward biased only when thyristor is off.


49. 

Assertion (A): An ideal rectifier should have unity harmonic factor

Reason (R): An ideal rectifier should have unity displacement factor.

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

Answer: Option D

Explanation:

Ideal rectifier should have zero harmonic factor and unity displacement factor.


50. 

A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30°, the dc output voltage will be about

A. 127 V
B. 120 V
C. 110 V
D. 100 V

Answer: Option B

Explanation:

Using Eq

= 0.933.

Hence Vdc for 30° firing angle = 0.933 x 127 = ≈ 120 V.


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