When the core of a saturable reactor is saturated, the inductance is high. True

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Question
When the core of a saturable reactor is saturated, the inductance is high.
Options
A. True
B. False

Correct Answer

False

Explanation

Since core is saturated, change of flux is small and inductance is low.

Power Electronics problems

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2. A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load
Options
A. rectification efficiency will be more than 0.6 and TUF will be more than 0.35
B. rectification efficiency will be more than 0.6 but TUF will be less than 0.35
C. rectification efficiency will be less than 0.6 and TUF will be less than 0.35
D. rectification efficiency will be less than 0.6 but TUF will be more than 0.35

3. An SCR has a turn on time of 4 ?s. The gate pulse should have a duration of about
Options
A. 2 ?s
B. 5 ?s
C. 20 ?s
D. 50 ?s

4. In a semi converter feeding a resistive load, the firing angle is a. Each thyristor conducts for
Options
A. p radians
B. (p - a) radians
C. (p + a) radians
D. (p - 0.5 a) radians

5. The gate current required to turn on an SCR is
Options
A. few amperes
B. a few mA
C. almost equal to anode current
D. about 50% of anode current

6. Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V.
Reason (R): When an SCR is conducting, the junction temperature is about 200�C.
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

7. A single phase full wave regulator feeds R-L load. The best gating signal is
Options
A. short duration pulses
B. long duration pulses
C. pulse train
D. either (a) or (b)

8. A cycloconverter cannot give a frequency higher than input frequency.
Options
A. True
B. False

9. A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if
Options
A. load torque is constant
B. load torque increases with increase in speed
C. load torque decreases with increase in speed
D. either (a) or (b)

10. Assertion (A): A cycloconverter may be line commutated or forced commutated
Reason (R): A step up cycloconverter requires forced commutation.
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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