In a 3 phase fully controlled converter the firing frequency is 3 times the line

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Question
In a 3 phase fully controlled converter the firing frequency is
Options
A. 3 times the line frequency
B. 6 times the line frequency
C. 9 times the line frequency
D. 12 times the line frequency

Correct Answer

6 times the line frequency

Explanation

It is a 6 pulse converter.

Power Electronics problems

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1. The terminals of a power MOSFET are called
Options
A. emitter, base, collector
B. source, gate, drain
C. source, base, drain
D. emitter, gate, drain

3. A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30�, the dc output voltage will be about
Options
A. 127 V
B. 120 V
C. 110 V
D. 100 V

4. An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is
Options
A. 16% maximum
B. 40% of maximum
C. 60% of maximum
D. 84% of maximum

5. The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by
Options
A. forward characteristics of thyristors
B. reverse recovery characteristics of thyristors
C. both forward and reverse recovery characteristics of thyristors
D. none of the above

6. In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally
Options
A. equal
B. different
C. equal or different
D. different but sometimes equal

7. The dynamic equalising circuit consists of a series combination of capacitor C and resistor R_C across each thyristor. This resistance R_C (along with parallel connected diode)
Options
A. limits charging current
B. limits discharging current
C. limits both charging and discharging currents
D. none of the above

8. A dc separately excited motor has constant field current. The armature is fed from a single phase supply through a full converter. When a = 0, speed is 500 rpm. If a = 45�, the speed is likely to be
Options
A. about 350 rpm
B. about 250 rpm
C. about 175 rpm
D. about 125 rpm

9. Two thyristor of same rating and same specifications
Options
A. will have equal turn on and turn off periods
B. will have equal turn on but unequal turn off periods
C. may have equal or unequal turn on and turn off periods
D. will have unequal turn on and turn off periods

10. In single phase half wave regulator, the average current over one full cycle
Options
A. is always positive
B. may be positive or negative
C. may be negative
D. is always negative

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