204. 1n a conventional reverse blocking thyristor
A. external layers are lightly doped and internal layers are heavily doped.
B. external layers are heavily doped and internal layers are lightly dooped
C. the p-layers are heavily doped and the n-layers are lightly doped
D. the p-layers are lightly doped and the n-layer are heavily doped.

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205. In order to obtain static voltage equalization in series-connected SCRs, connections are made of
A. one resistor acrossthe string
B. resistors of different values across each SCR
C. resistors of the same value across each SCR
D. one resistor in series with the string

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206.  Consider the following statements : The overlap angle of a phase-controlled converter would in crease on increasing the 1. supply voltage 2. suply frequency 3. load current 4. source inductance Of these statements
A. 1, 2 and 3 are correct
B. 2, 3 and 4 are correct
C. 1, 2 and 4 are correct
D. 1, 3 and 4 are correct

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207. Analysis of voltage waveform of a single phase bridge converter shows that it contains x% of 6th harmonic. The 6th harmonic content of the voltage waveform of a 3-phase bridge converter would be
A. less than x% due to an increase in the number of pulses
B. equal to x%, the same as that of the single phase converter
C. greater than x% due to changes in the input and output voltages of the converter
D. difficult to predict as the analysis of converters is not governed by any generalised theory

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208.  Use of a reverse conducting thy ristor in place of antiparallel combination of thyristor and feedback diode in an inverter
A. effectively minimises the peak commutating current
B.in the rotor decreases the opeating frequency of operation
C. minimises the effects of lead inductances on the commutation performance
D. causes deterioration in the commutation performance

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209. A voltage source inverter is normally employed when
A. source inductance is large and load inductance is small
B. source inductance is small and load inductance is large
C. both source and load inductance are small
D. both source and load inductances are large

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210. Consider the following statements : The diodes in a voltage source inverter (Mc Murry inverter) should be able to 1. withstand a large voltage in the reverse direction 2. carry the commutating*current excess of load current. 3. provide the required reverse bias to the outgoing thyristor. 4. feedback the reactive current to the source Of these statements
A. 1,2 and 3 are correct
B. 1, 3 and 4 are correct
C. 2,3 and 4 are correct
D. 1,2 and 4 are correct

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