Power Electronics-Engineering-Nov2019 - Grad Plus

Power Electronics-Engineering-Nov2019

T.E. (E & TC)
(2015 Pattern)

Time : 2½ Hours
Max. Marks : 70
Instructions to the candidates:
1) Answer Q.1 or Q.2, Q.3 or Q.4, Q.5 or Q.6 and Q.7 or Q.8.
2) Neat diagrams must be drawn wherever necessary.
3) Figures to the right side indicate full marks.
4) Assume Suitable data if necessary.
5) Use of Calculator is allowed.

Q1) a) Draw the dynamic characteristics of SCR and explain the turn on & turn off process of SCR in detail? [7M]

b) With the help of neat circuit diagram & waveforms explain the operation of 3-φ semi converter for R-load with α = 60º. [7M]

c) List out the different voltage control techniques used in inverters? Explain any one in detail? [6M]


Q2) a) Draw & explain steady state characteristics of power MOSFET? [6M]

b) Explain the operation of symmetric 1.φ semi converter with continuous load current. Draw the waveforms and state the eqn for average o/p voltage. [7M]

c) Explain 1-φ full bridge inverter for RL load using MOSFET Draw necessary ckt dig & waveforms. [7M]

Q3) a) Draw & explain step down chopper for R-load with circuit dig. & waveforms. Derive expression for avg o/p voltage? [8M]

b) Derive the expression for average o/p voltage of step up chopper. A step up chopper has i/p voltage of 220v & o/p voltage of 660v. if the non conducting time is 100 μ sec. Calculate pulse width of o/p voltage. Also find the new o/ p voltage if pulse width is half for constant frequency operation [8M]


Q4) a) With the help of circuit dig & waveforms. Explain the operation of 1-φ full wave Ac voltage controller with R-load? Derive the expression for rms o/p voltage? [8M]

b) Derive the expression for average o/p voltage of step down chopper. If DC chopper has resistive load of R = 10Ω and the i/p DC voltage is 300v. When the chopper switch remains on its voltage drop is 2v and the chopping freq is 1kHz. If duty cycle is 40% determine. [8M]
i) Average o/p voltage
ii) rms o/p voltage
iii) Form factor
iv) Ripple factor

Q5) a) What is meant by electromagnetic interference? Explain it’s sources and different minimization techniques in detail? [10M]

b) Explain the over voltage protection ckt using selenium diode & Mov to protect the power devices in detail? [8M]


Q6) a) What is Resonant converters? Explain the concept of ZCS and ZVS using ckt dig. & waveforms [10M]

b) What are the different cooling methods used for protection of power devices? Explain in detail. [8M]

Q7) a) With the help of block dig explain the operation of electronic ballast in detail? [8M]

b) What is online? Offline ups? Explain block diagram and applications?[8M]


Q8) a) With the help of neat ckt dig. explain the operation of fan Regulator ckt using TRIAC. [8M]

b) A ups is driving a 600 kl load which has a lagging p.f. of 0.8. The efficiency of the inverter is 80%. The battery voltage is 24v DC. Assume that there is a separate charger for the battery. Determine [8M]
i) KVA rating of the inverter
ii) Wattage of Rectifier
iii) A.H. rating of battery for backup time of 30 min.

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