A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator

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Question
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)

Correct Answer

load torque increases with increase in speed

Explanation

If load torque is constant, the change in speed is very small.

Power Electronics problems

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

2. 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)

3. 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

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

6. 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

8. A single phase electric heater uses phase controlled thyristors. The firing angle is 90�. The degree of heating is
Options
A. 25% of maximum
B. 50% of maximum
C. 75% of maximum
D. none of the above

9. In a single phase full bridge converter (B - 2 connection), the input voltage is v = V_m sin ?t. The output dc voltage for resistive load
Options
A.
B.
C.
D.

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