Power Electronics - Section 1 (4)
Power Electronics - Section 1
| 25. | Current derating may be necessary when thyristors are operating in |
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Answer: Option B Explanation: Since current does not divide equally, current derating is necessary. |
| 26. | 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 |
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Answer: Option B Explanation: When freewheeling diode conducts output current exists but output voltage is zero. |
| 27. | 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) |
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Answer: Option B Explanation: Discharge current flows through Re . |
| 28. | In single phase half wave regulator, the average current over one full cycle |
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Answer: Option D Explanation: The input current during positive half cycle is less than that during negative half cycle. |
| 29. | The terminals of a power BJT are called |
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Answer: Option A Explanation: In a BJT terminals are emitter, base and collector irrespective of rating. |
| 30. | 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 |
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| 31. | An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is |
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Answer: Option B Explanation: Vl = V √a. Therefore Vl2 - V2 (a). Heating is proportional to a. |
| 32. | In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally |
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Answer: Option A Explanation: Firing angles are kept equal to get symmetrical output voltage. |