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Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 3
6.
In a single phase dual converter, a1, and a2 are firing angles of the two converters. Then
a1 - a2 =
a1 + a2 = p
a1 - a2 = p
a1 + a2 =
Answer: Option
Explanation:

Since one converter is rectifying and the other is inverting

Vdc1 = -Vdc2

or a1 + a2 = p.

7.
The number of gates in an SCR is
1
3
4
6
Answer: Option
Explanation:
No answer description is available. Let's discuss.
8.
The waveshape of output voltage of half bridge inverter is
sinusoidal
square
triangular
either (a) or (b)
Answer: Option
Explanation:
No answer description is available. Let's discuss.
9.
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
about 1350 rpm
about 720 rpm
about 360 rpm
either (b) or (c)
Answer: Option
Explanation:

In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.

10.
The gate current required to turn on an SCR is
few amperes
a few mA
almost equal to anode current
about 50% of anode current
Answer: Option
Explanation:

Only a very small gate current is required to trigger SCR into conduction.

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