136. 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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137. When the firing angle α of a single phase, fully controlled rectifier feeding constant d.c. current into a load is 30°, the displacement power factor of the rectifier is ______ .

1. 1. 0.5

   
   
   

   2. 1.5

   
   
   

   3. 5

   
   
   

   4. 15

   
   
   

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   NA

   Correct Option: A

   NA

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138. If in a 3-phase, half-wave rectifier, if per phase input voltage is 200 V, then average output voltage is ______ V.

1. 1. 233.91

   
   
   

   2. 33.91

   
   
   

   3. 333.91

   
   
   

   4. None of the above

   
   
   

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   Since V_t = 200 V, therefore
   table>V_o =

   3 √2 V_ph = 3 √2 × 200 = 233.91 Vπ3.1414

   Correct Option: A

   Since V_t = 200 V, therefore
   table>V_o =

   3 √2 V_ph = 3 √2 × 200 = 233.91 Vπ3.1414

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139. A dc source of 100 V supplies a purely inductive load 0.1 H. The controller is a thyristor in series with the source and load. The latching current specified is 100 mA. The minimum width of the gating pulse to ensure thyristor turn ON is ______ s .
     

1. 1. 100

   
   
   

   2. 200

   
   
   

   3. 500

   
   
   

   4. 1000

   
   
   

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   For an inductive load,
   

   V = L	di	=	LI
   	dt		T

   
   

   ⇒ T =	LI	=	0.1 × 100 × 10-3	= 0.1 ms or 100 μs
   	V		100

   
   

   Correct Option: A

   For an inductive load,
   

   V = L	di	=	LI
   	dt		T

   
   

   ⇒ T =	LI	=	0.1 × 100 × 10-3	= 0.1 ms or 100 μs
   	V		100

   
   

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140. The circuit in the figure shows zener regulated dc power supply. The zener diode is ideal. The minimum value of RL down to which the output voltage remain constant, is ______ Ω .
     

1. 1. 15

   
   
   

   2. -45

   
   
   

   3. 45

   
   
   

   4. 90

   
   
   

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   I =	24 - 15	=	1	A ; and VL = 15 V
   	27		3

   
   

   ∴ RL =	VL	=	15	= 45 Ω
   	I		1 / 3

   Correct Option: C

   I =	24 - 15	=	1	A ; and VL = 15 V
   	27		3

   
   

   ∴ RL =	VL	=	15	= 45 Ω
   	I		1 / 3

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