A 3 phase induction motor is controlled by voltage and frequency control such th

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Question
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque
Options
A. will be less than 100 N-m
B. will be more than 100 N-m
C. may be more or less than 100 N-m depending on motor parameters
D. very small

Correct Answer

will be more than 100 N-m

Power Electronics problems

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1. A UJT exhibits negative resistance characteristics when
Options
A. Current is less than valley current
B. Current is less than peak current
C. Current is more than peak current but less than valley current
D. None of the above

5. Two single phase semi-converters are connected in series to form a series converter. The input is v = V_m sin ?t and a₁, a₂ are the firing angles. If a₁ = 0, the dc output voltage is
Options
A. (1 + cos a₂)
B. (2 + cos a₂)
C. (3 + cos a₂)
D. (4 + cos a₂)

9. A class A chopper has an input voltage of 200 V. T_on = 1.5 ms and T_off = 4.5 ms. The duty cycle, average output voltage and ripple factor respectively are
Options
A. 0.5, 100 V and 1
B. 0.25, 50 V and 3
C. 0.25, 50 V and 1
D. 0.5, 100 V and 3

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