| POWER ELECTRONICS |
| PAPER NO. 3 |
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EC POWER ELECTRONICS (B.Tech 4th Semester,1202) Time : 3 Hours Maximum Marks : 60 NOTE:- This paper consist of Three Sections. Section A is compulsory. Do any Four questions from Section B and any two questions from Section C Section-A Marks : 20 1(a) Discuss the conditions which must be satisfied for turning on SCR with a gate signal. (b) Is turn-on time of SCR is constant ? On what factor does it depend? (c) Name two main types of inverters and distinguish the two. (d) What is Cyclo-convertor ? Enumerate some of its industrial applications. (e) Name some applications of Dielectric heating and what it is ? (f) Name applications of IC 555. (g) What are dielectric properties of materials in general ? (h) Name different methods of speed control of I-M. (i) Explain free-wheeling diode. (j) Explain DIAC and its V-I characteristics. Section-B Marks:5 Each 2. Show that string efficiency of two parallel connected SCRs is usually less that 1 and also discuss the problems associated with the parallel operation of SCRs and how these are overcome. 3. A single-phase half-wave SCR circuit feeds power to resistive load. Draw waveforms for source voltage, load voltage and voltage across SCR for a given firing angle α. Hence obtain expression for average and r.m.s. voltages in terms of source voltage and firing angle. 4. Discuss the main d.c. to d.c. thyristor converters. Which of these is more commonly employed and why ? 5. Classify different types of power supplies. For these types, explain different conversion schemes employed solid state devices. Give their applications also. 6. Explain the circuit for reversing the speed of motors. Section-C Marks : 10 Each 7. Describe the operation principle of single-phase to single-phase step-up cycloconverter with the help of mid-point and bridge type configuration. Enumerate some of industrial applications of cyclo-converters. 8. Discuss the working of a single-phase half bridge inverter. What is its main drawback ? How is this drawback overcome ? 9. Write notes on the following: (a) T-N characteristics of I-M inverters (b) SCR-delay timer. |
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