Electronics and Communication Engineering - Power Electronics

16. 

A thyristor has its gate current zero. To start conduction the forward voltage must exceed

A. about 0.5 V
B. forward breakover voltage
C. on state voltage
D. peak working off state forward voltage

Answer: Option B

Explanation:

With zero gate current, conduction can be started only if forward voltage exceeds breakover voltage.


17. 

Assertion (A): Snubber circuit has an RC series circuit in parallel with SCR

Reason (R): Voltage across a capacitor can not change instantaneously.

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

Answer: Option A

Explanation:

Since voltage across capacitor cannot change instantaneously it protects SCR against high .


18. 

In dielectric heating, the thyristor circuits consist of

A. rectifier-chopper combination
B. controlled rectifier
C. ac regulator
D. rectifier-inverter combination

Answer: Option D

Explanation:

Input ac is rectified and then converted to high frequency ac.


19. 

On load tap changer using thyristors can have a maximum of two taps.

A. True
B. False

Answer: Option B

Explanation:

Any number of taps are possible.


20. 

Assertion (A): A cycloconverter may be line commutated or forced commutated

Reason (R): A step up cycloconverter requires forced commutation.

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

Answer: Option A

Explanation:

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