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Electronics Engineering Objective Questions { Power Semiconductor Devices and Their Applications }

197. An inverter capable of supplying a balanced three-phase variable voltage, not cause variable frequency output is feeding a three-phase induction motor rated for 50 Hz and 440 V. The stator winding resistance of the motor are negligibly small. During starting, the current in such can be avoided without sacrificing the starting torque be suitable applying
A. low voltage at rated frequency
B. low voltage keeping the V/I ratio constant
C. rated voltage at low frequency
D. rated voltage at rated frequency
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198. In a 3-phase, half-wave diode rectifier, the ratio of average output voltage to per phase maximum a.c. voltage as
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199. If in a 3-phase, half-wave rectifier, if per phase input voltage is 200 V, then the average output voltage is
A. 233.91 V
B. 116.95V
C. 202.56 V
D. 101.28 V
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200. A voltage commutated chopper has the following parameters : Vs = 200 V, load circuit parameter la 2mH,5V.Commutation circuit parameter : L =25 pH, C = 50 p.F. For constant load current at 100A, the effective on period and peak current through the main thyristor respectively
A. 1000 gS, 200A
B. 700 gS, 382.8A
C. 700 S, 282.8A
D. 10001.6, 382.8 A
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201. In type A chopper source voltage is 100 V, d.c. on period = 100 RS, off-period = 150 itS and loadRLE consists of R = 20, L = 5 mH, E = 10V. For continuous conduction average output voltage and average output current for this chopper are respectively
A.40 V, 15A
B. 66.66 V 28.33A
C. 60 V, 25A
D. 40 V, 20 A
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202. The average on-state current for an SCR is 20 A for a conduction angle of 120?. The average on-state current for 60? conduction angle will be
A. 20A
B. 10 A
C. less than 20 A
D. 40 A
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203. The average on-state currentfor an SCR is 20A for a resistive load. If an inductance at 5 mH is included in the load, then average on-state current would be
A. more than 20 A
B. less than 20 A
C. 15 A
D. 20 A
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