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Power Electronics problems

1. The method of triggering SCS is
Options
A. application of positive pulse at cathode gate or negative pulse at anode gate
B. application of pulse at anode gate
C. application of pulse at cathode gate
D. application of low voltage at anode

2. A fully controlled bridge converter is feeding an RLE load. The load current is I₀. The input voltage is V_m sin ?t. The KVL equation to find firing angle a is
Options
A. cos a = E + I₀R
B. cos a = E + I₀R
C. cos a = E - I₀R
D. cos a = E - I₀R

4. When thyristors are connected in parallel, the current distribution may become non-uniform due to
Options
A. inductive effect of current carrying conductors
B. capacitive effect of current carrying conductors
C. both inductive and capacitive effects
D. none of the above

5. In a bridge inverter with single pulse width modulation
Options
A. the output frequency is equal to frequency of reference signal
B. the output frequency is equal to frequency of control signal
C. either (a) or (b)
D. neither (a) nor (b)

6. For a single phase half wave converter feeding a resistive load, the firing angle a. The waveshape in below figure is for
Options
A. output voltage
B. input voltage
C. voltage drop across thyristor
D. none of the above

8. A LASCR has
Options
A. 4 semiconductor layers and 3 junctions
B. 3 semiconductor layers and 2 junctions
C. 2 semiconductor layers and 2 junctions
D. any of these depending on the rating

9. Assertion (A): Thyristors can be used in controlled heating, excitation systems of alternators, speed control of motors and HVDC
Reason (R): A static var system using thyristors is very commonly used in high voltage ac systems.
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

10. A dc series motor is coupled to a load whose torque is proportional to speed. It is fed by a single phase ac supply through a full converter. When speed is 500 rpm, firing angle is 45�. It is desired to raise the speed. It will be necessary to
Options
A. decrease the firing angle
B. increase the firing angle
C. either decrease or increase the firing angle depending on the required speed
D. decrease the load torque

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