111. The fully controlled thyristor converter in the given figure is fed from a single-phase source. When the firing angle is 0°, the dc output voltage of the converter is 300 V. What will be the output voltage for a firing angle of 60°, assuming continuous conduction?
     
     

1. 1. 150 V

   
   
   

   2. 210 V

   
   
   

   3. 300 V

   
   
   

   4. 100 π V

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   For Fully Controlled Converter (FCC)
   

   Average output voltage, V0 =	2 √2 V	cos α (V = rms)
   	π

   
   For α = 0, V₀ = 300
   

   ∴ 300 =	2 √2	.V
   	π

   
   

   ⇒ V =	300 π
   	2 √2

   
   

   A α = 60 , V0 =	2 √2		300π		.cos 60
   	π		2 √2

   
   

   = 300 ×	1	= 150 V
   	2

   Correct Option: A

   
   For Fully Controlled Converter (FCC)
   

   Average output voltage, V0 =	2 √2 V	cos α (V = rms)
   	π

   
   For α = 0, V₀ = 300
   

   ∴ 300 =	2 √2	.V
   	π

   
   

   ⇒ V =	300 π
   	2 √2

   
   

   A α = 60 , V0 =	2 √2		300π		.cos 60
   	π		2 √2

   
   

   = 300 ×	1	= 150 V
   	2

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112. The power electronic converter shown in the figure given below has a single-pole double-throw switch. The pole P of the switch is connected alternately to throws A and B. The converter shown is a
     
     

1. 1. step-down chopper (buck converter)

   
   
   

   2. half-wave rectifier

   
   
   

   3. step-up chopper (boost converter)

   
   
   

   4. full-wave rectifier

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   Let Duty cycle be ‘D’.
   When at A : t = 0
   

   Vin = L	di	+ Vout , (iL)in =	(Vin - V0)	DT
   	dt		L

   
   When at B : At t = DT
   

   Vout = -VL =	-LdiL
   	dt

   
   

   (iL)off =	-Vout	(1 - D)T
   	L

   
   (V_in – V_out) DT + (– V_out) (1 – D)T = 0
   ⇒ (V_in – V_out) D = V_out(1 – D)
   ⇒ V_out = DV_in and D < 1
   So, step down chopper.
   

   Correct Option: A

   
   Let Duty cycle be ‘D’.
   When at A : t = 0
   

   Vin = L	di	+ Vout , (iL)in =	(Vin - V0)	DT
   	dt		L

   
   When at B : At t = DT
   

   Vout = -VL =	-LdiL
   	dt

   
   

   (iL)off =	-Vout	(1 - D)T
   	L

   
   (V_in – V_out) DT + (– V_out) (1 – D)T = 0
   ⇒ (V_in – V_out) D = V_out(1 – D)
   ⇒ V_out = DV_in and D < 1
   So, step down chopper.
   

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113. A voltage commutated chopper circuit, operated at 500 Hz, is shown below.
     
     If the maximum value of load current is 10 A, then the maximum current through the main (M) and auxiliary (A) thyristors will be
     

1. 1. i _{M max} = 12 A and i_{A max} = 10 A

   
   
   

   2. i _{M max} = 12 A and i_{A max} = 2 A

   
   
   

   3. i _{M max} = 10 A and i_{A max} = 12 A

   
   
   

   4. i _{M max} = 10 A and i_{A max} = 8 A

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   i_Amax = I_o = 10 A

   Correct Option: A

   
   i_Amax = I_o = 10 A

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114. A lossy capacitor C_x, rated operation at 5 kV, 50 Hz is represented by an equivalent circuit with an ideal capacitor C_p is parallel with a resistor R_p. The value of C_p is found to be 0.102 μF and the value of R_p = 1.25 MΩ. Then the power loss and tan δ of the lossy capacitor operating at the rated voltage, respectively, are
     

1. 1. 10 W and 0.0002

   
   
   

   2. 10 W and 0.0025

   
   
   

   3. 20 W and 0.025

   
   
   

   4. 20 W and 0.04

   
   
   

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1. View Hint View Answer Discuss in Forum

   Power - loss =	V2		(5 KV)2	= 20 W
   	RP		1.25 MΩ

   
   

   tan δ =	1
   	ωCP RP

   
   

   =	1	= 0.025
   	(2π 50)(0.102 × 10-6)(1.25 × 106)

   
   
   

   Correct Option: C

   Power - loss =	V2		(5 KV)2	= 20 W
   	RP		1.25 MΩ

   
   

   tan δ =	1
   	ωCP RP

   
   

   =	1	= 0.025
   	(2π 50)(0.102 × 10-6)(1.25 × 106)

   
   
   

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115. Circuit turn-off time of an SCR is defined as the time
     (a)
     (b)
     (c)
     (d)
     

1. 1. taken by the SCR to turn off

   
   
   

   2. required for the SCR current to become zero

   
   
   

   3. for which the SCR is reverse biased by the commutation circuit

   
   
   

   4. for which the SCR is reverse biased to reduce its current below the holding current

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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