electronics-and-communication-engineering-power-electronics Related Question Answers

1. A semiconverter feeding an RLE load operates in





2. The phenomenon of overlap in converter operation due to





3. 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





4. For a 12 pulse operation, the two 6 pulse units are fed by





5. 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





6. 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





7. The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes





8. In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is





9. Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.



10. Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time.





11. The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by





12. A chopper





13. Assertion (A): If the duty cycle of chopper is low the current would not become discontinuousReason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.





14. In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally





15. An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is





16. 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





17. The terminals of a power BJT are called





18. In single phase half wave regulator, the average current over one full cycle





19. 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)





20. 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





21. Current derating may be necessary when thyristors are operating in





22. If duty cycle is a and the load is a resistance R, the rms value of output voltage is



23. For a BJT a = 0.98, then β =





24. Assertion (A): Power transistor has lower switching time than SCR Reason (R): Power transistor has greater switching time than SCR





25. A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is





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