Assertion (A): Thyristors can be used in controlled heating, excitation systems

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Question
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

Correct Answer

Both A and R correct but R is not correct explanation of A

Power Electronics problems

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1. 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

3. 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

4. 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)

5. 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

6. 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

9. A fully controlled bridge converter feeds a highly inductive load such that the load current can be assumed to be constant. The wave shape of input current is
Options
A. dc
B. sinusoidal
C. rectangular
D. none of the above

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