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 = Vm sin ωt. The thyristor will conduct
A:
from 0 to 180°
B:
when v > 50 V
C:
from 0 to 90°
D:
When v < 50 V
Answer:B
Thyristor can conduct only when it is forward biased. This occurs only when v > 50 V.
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The gate current required to turn on an SCR is
A:
few amperes
B:
a few mA
C:
almost equal to anode current
D:
about 50% of anode current
Answer:B
Only a very small gate current is required to trigger SCR into conduction.
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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
A:
about 1350 rpm
B:
about 720 rpm
C:
about 360 rpm
D:
either (b) or (c)
Answer:B
In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.
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The waveshape of output voltage of half bridge inverter is
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