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Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 1
6.
A semiconverter feeding an RLE load operates in
first quadrant only
first and second quadrants
first and fourth quadrants
first and third quadrants
Answer: Option
Explanation:

Semiconvertor operates only in first quadrant.

7.
The phenomenon of overlap in converter operation due to
source resistance
source inductance
both source resistance and source inductance
high value of firing angle
Answer: Option
Explanation:

Source inductance delays turn off and hence causes overlap.

8.
A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is
20 W
50 W
92 W
128 W
Answer: Option
Explanation:

.

9.
For a 12 pulse operation, the two 6 pulse units are fed by
Y - Y and Y - Y transformers
Δ - Δ and Δ - Δ transformers
Y - Y and Y - Δ transformers
Y - Δ and Y - Δ transformers
Answer: Option
Explanation:

30° phase difference is necessary.

10.
In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
p - a
p
p + a
p - 2a
Answer: Option
Explanation:

Since conduction is from a to p + a, period of conduction is p in each half cycle.

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