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Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 1
21.
A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is Is and rms value of load current in Irms. Then
Is = Irms irrespective of the value of firing angle
Is = 0.5 Irms irrespective of the value of firing angle
Is = Irms if firing angle is less than 30°
Is = Irms if firing angle is more than 30°
Answer: Option
Explanation:

.

22.
The terminals of a power BJT are called
emitter, base, collector
emitter, base, drain
source, base, drain
source, base, collector
Answer: Option
Explanation:

In a BJT terminals are emitter, base and collector irrespective of rating.

23.
In single phase half wave regulator, the average current over one full cycle
is always positive
may be positive or negative
may be negative
is always negative
Answer: Option
Explanation:

The input current during positive half cycle is less than that during negative half cycle.

24.
The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode)
limits charging current
limits discharging current
limits both charging and discharging currents
none of the above
Answer: Option
Explanation:

Discharge current flows through Re .

25.
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current
are similar
are not similar
may be similar or dissimilar
are similar only if firing angle is zero
Answer: Option
Explanation:

When freewheeling diode conducts output current exists but output voltage is zero.

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