Exercise: Power Electronics

Questions for: Power Electronics

The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes
A:
about 100 times
B:
about 10 times
C:
about 3 times
D:
about twice
Answer: C

v ∝ (i)1/4 ∝ (100)1/4 ≈ 3.

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An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be
A:
50 A
B:
25 A
C:
less than 50 A but more than 25 A
D:
less than 25 A
Answer: C

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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
A:
p - a
B:
p
C:
p + a
D:
p - 2a
Answer: B

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

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For a 12 pulse operation, the two 6 pulse units are fed by
A:
Y - Y and Y - Y transformers
B:
Δ - Δ and Δ - Δ transformers
C:
Y - Y and Y - Δ transformers
D:
Y - Δ and Y - Δ transformers
Answer: C

30° phase difference is necessary.

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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
A:
20 W
B:
50 W
C:
92 W
D:
128 W
Answer: B

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