| POWER ELECTRONICS |
| PAPER NO. 1 |
 |
 |
 |
|
| PUT ON: Dec, 2K2 |
|
EC POWER ELECTRONICS (B.Tech 4th Semester,2122) 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) Differentiate between latching and holding current. (b) What do you understand by string efficiency ? Explain. (c) What is intrinsic stand off ratio? What is its pracrical value? (d) Draw V.I. characteristics of UJT and label it. (e) Explain the term Transformer Utility Factor. (f) Write various applications of Cyclo-convertors. (g) What are the advantages of a full wave rectifier over half wave rectifier? (h) What is the purpose of rectangular ina power supply? (i) Explain why SCR is made of Si not of Ge. (j) Draw the symbols for SCR, DIAC, TRIAC,LASCR. Section-B Marks:5 Each 2. With the help of transister analogy, explain the working of SCR. 3. Using the single phase half-wave controlled circuit with commutating diode, a low voltage load is supplied by a 20 V ac supply. Assuming continuous load corrent, calculate the average load voltage for ∞ = 30o. Assume forward voltage drop of 1.5 V and 0.7 V across the thyristor and diode respectively. 4. With suitable waveforms, explain the working of full Bridge inverter. 5. What do you understand by IC timers? Explain the working of 555 timer in Astable mode. 6. Explain the working of Universal motor speed control circuit. Section-C Marks : 10 Each 7.(a) What do you understand by skin effect? How is it useful for heating of metals? (b) Show that skin depth has the dimension of length. 8.(a) What are various causes of instability of AC motors? Explain. (b) Draw T-N characteristics of induction motor and how cycloconvertor can be used for speed control of ac motors? 9. Write short notes on: (a) DUAL Converters (b) PWM Inverters. |