For a 12 pulse operation, the two 6 pulse units are fed by Y - Y and Y - Y trans

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Question
For a 12 pulse operation, the two 6 pulse units are fed by
Options
A. Y - Y and Y - Y transformers
B. ? - ? and ? - ? transformers
C. Y - Y and Y - ? transformers
D. Y - ? and Y - ? transformers

Correct Answer

Y - Y and Y - ? transformers

Explanation

30� phase difference is necessary.

Power Electronics problems

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4. The characteristics of a non-linear resistance is i = kv⁴. If i becomes 100 times, v becomes
Options
A. about 100 times
B. about 10 times
C. about 3 times
D. about twice

5. A thyristor has a maximum allowable junction temperature of 120�C and the ambient temperature is 40�C. If thermal resistance is 1.6� C/W, the maximum allowable internal power dissipation is
Options
A. 20 W
B. 50 W
C. 92 W
D. 128 W

6. In a step down chopper using pulse width modulation, T_on = 3 x 10^-3 and T_off = 1 x 10^-3 s. The chopping frequency is
Options
A. 333.33
B. 250
C. 500
D. 1000

7. A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is I_s and rms value of load current in I_rms. Then
Options
A. I_s = I_rms irrespective of the value of firing angle
B. I_s = 0.5 I_rms irrespective of the value of firing angle
C. I_s = I_rms if firing angle is less than 30�
D. I_s = I_rms if firing angle is more than 30�

8. Assertion (A): Power transistor has lower switching time than SCR
Reason (R): Power transistor has greater switching time than SCR
Options
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

9. In a single phase full wave converter (M-2 connection) feeding on R - L load, the input voltage is v = V_m sin ?t. The expression for dc output voltage is
Options
A.
B.
C.
D.

10. An SCR is triggered at 40� in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80�, the average anode current is likely to be
Options
A. 50 A
B. 25 A
C. less than 50 A but more than 25 A
D. less than 25 A

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