71. A 3 phase, fully controlled, converter is feeding power into a d.c. load at a constant current of 150 A. The rms current through each thyristor of the converter is ______ A .

1. 1. 	150
      	√3

      
      

   
   
   

   2. 150 √3

   
   
   

   3. √3

   
   
   

   4. None of the above

   
   
   

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   NA

   Correct Option: A

   NA

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72. In the single phase diode bridge rectifier shown in the given figure, the load resistor is R = 50 Ω; source voltage is v = 200 sinωt, where ω2π × 50 radians per second. The power dissipated in the load resistor R is ______ W.
    
    

1. 1. 40

   
   
   

   2. 200

   
   
   

   3. 400

   
   
   

   4. 800

   
   
   

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   NA

   Correct Option: C

   NA

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73. A six pulse thyristor rectifier bridge is connected t o a balanced 50 Hz, three phase ac source. Assuming that the dc output current of the rectifier is constant, the lowest frequency harmonic component in the ac source line current is ______ Hz

1. 1. 150

   
   
   

   2. 250

   
   
   

   3. 450

   
   
   

   4. 550

   
   
   

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   NA
   

   Correct Option: B

   NA
   

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74. A 3-phase full converter has an average output voltage of 200 V for zero degree firing angle and for resistive load. For a firing angle of 90°, the output voltage would be ______V
    

1. 1. 0

   
   
   

   2. 1

   
   
   

   3. 2

   
   
   

   4. 3

   
   
   

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   Vo =	3 Vmc	cos α
   	n

   
   For α = 90° , V_o = 0V

   Correct Option: A

   Vo =	3 Vmc	cos α
   	n

   
   For α = 90° , V_o = 0V

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75. In dc-chopper, per unit ripple is maximum when duty cycle α is ______ .
    

1. 1. 0.5

   
   
   

   2. 5

   
   
   

   3. 0.05

   
   
   

   4. 1.5

   
   
   

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   NA

   Correct Option: A

   NA

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