To protect an SCR against high di/dt we connect a capacitance in series with SCR

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Question
To protect an SCR against high di/dt we connect
Options
A. a capacitance in series with SCR
B. a capacitance in parallel with SCR
C. an inductance in parallel with SCR
D. an inductance in series with SCR

Correct Answer

an inductance in series with SCR

Explanation

current through inductance cannot change instantaneously.

Power Electronics problems

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1. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
Options
A. about 1350 rpm
B. about 720 rpm
C. about 360 rpm
D. either (b) or (c)

2. A thyristor has maximum allowable junction temperature of 110� C and the ambient temperature is 40�C, If the maximum internal power dissipation is 50 W, the thermal resistance is
Options
A. 2� C/W
B. 1.4� C/W
C. 0.7�C/W
D. 2.2� C/W

3. Assertion (A): A high dv/dt may cause triggering of a thyristor.
Reason (R): A high dv/dt results in charging current in the thyristor.
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

6. A single phase half wave regulator uses
Options
A. 2 diodes and 2 thyristors
B. 2 thyristors
C. 1 diode and 1 thyristor
D. 2 diodes

7. A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20�C. If thermal resistance is 1.6� C/W, the junction temperature is
Options
A. 114�C
B. 164�C
C. 94� C
D. 84� C

8. In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is
Options
A. 30�
B. 60�
C. 90�
D. 120�

9. A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = V_m sin ?t. The thyristor will conduct
Options
A. from 0 to 180�
B. when v > 50 V
C. from 0 to 90�
D. When v < 50 V

10. Assertion (A): A GTO circuit is more compact than SCR circuit
Reason (R): A GTO can be turned off by negative gate pulse.
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

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