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Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 1
16.
The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by
forward characteristics of thyristors
reverse recovery characteristics of thyristors
both forward and reverse recovery characteristics of thyristors
none of the above
Answer: Option
Explanation:

Value of C is proportional to maximum difference between reverse charge of SCRs in series.

17.
A chopper
converts constant voltage dc into ac and then into variable voltage dc
converts constant voltage dc into variable voltage dc directly
converts ac of one frequency into ac of another frequency
converts ac to dc
Answer: Option
Explanation:

A chopper is a dc-dc converter. It converts a fixed dc voltage into a variable dc voltage.

18.

Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous

Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.

Both A and R are correct and R is correct explanation of A
Both A and R correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Answer: Option
Explanation:

If duty cycle is low, current may become discontinuous.

19.
In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally
equal
different
equal or different
different but sometimes equal
Answer: Option
Explanation:

Firing angles are kept equal to get symmetrical output voltage.

20.
An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is
16% maximum
40% of maximum
60% of maximum
84% of maximum
Answer: Option
Explanation:

Vl = V a. Therefore Vl2 - V2 (a). Heating is proportional to a.

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