Question 51 : What is the expression for the value of the capacitor in the voltage commutation circuit? Let tc be the circuit turn off time and Io be the constant load current.
1. Io x (dv/dt)
2. Vs/Io
3. (tc x Io)/Vs
4. none of the mentioned
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Question 52 : A voltage commutated chopper feeds power to an electric car (battery-powered). The battery voltage is 60 V. Starting current is 60 A and the SCR turn-off time is 20 μs. Calculate the value of inductance (L) required for the commutating circuit.
1. 400 μH
2. 40 nH
3. 40 μH
4. 0.4 mH
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Question 53 : In case of a constant frequency system, Ton = (1/4)T. If the chopping frequency 2 kHz, find the value of Toff.
1. (1/8) ms
2. (3/8) ms
3. (1/8) μs
4. (3/8) μs
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Question 54 : A type D chopper is a
1. two quadrant type-B chopper
2. two quadrant type-A chopper
3. two quadrant type-C chopper
4. none of the mentioned
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Question 55 : Which type of commutation circuit does not work on no load?
1. Voltage commutation
2. Current commutation
3. Both voltage and current commutation
4. None of the mentioned
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Question 56 : In case of TRC (Time Ratio Control), _________ is varied
1. duty cycle
2. firing angle
3. supply frequency
4. supply voltage magnitude
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Question 57 : Find the average output voltage for a type D chopper if it is given a dc supply of 220 V. Chopper frequency is 2 kHz and both the chopper switches are operated for 0.3 ms.
1. 220 V
2. 108 V
3. 98 V
4. 44 V
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Question 58 : In current commutated copper circuit
1. the capacitor cannot charge on no load
2. the auxiliary thyristor is turned on automatically
3. the auxiliary thyristor is naturally commutated
4. the commutation is not reliable
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Question 59 : A step down chopper has input dc voltage of 220 V and R = 10 Ω in series with L = 65 mH. If the load current varies linearly between 11 A and 17 A, then find the duty cycle α.
1. 1
2. 0.4
3. 0.6
4. 0.7
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Question 60 : Which type of chopper is used in the regenerative braking of DC motors?
1. type A
2. type B
3. type C
4. type D
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