Power Electronics 2018 Question Paper — Government College of Enginee…

The 2018 Power Electronics previous year question paper (Government College of Engineering and Technology, Jammu), with every question and its marks.

Instructions

Attempt five questions in all selecting at least two questions from each Section.
Each question carries 20 marks.
Assume missing data if any.

Attempt at least two questions from this Section.

Q1. a) Explain the methods adopted for protection of SCRs against overcurrents. b) Describe briefly the following members of Thyristor family:- DIAC, PUT and UJT Illustrate your answer with suitable diagrams. [20 marks]
Q2. Discuss the two-transistor model of a Thyristor. Derive an expression for the anode current and discuss therefrom the turn-on mechanisms of a thyristor. [20 marks]
Q3. a) Describe the principle of operation of single-phase half-wave phase-controlled rectifier circuit using RLE load with suitable circuit diagram and waveforms. b) A single-phase transformer, with secondary voltage of $230\text{ V}$, $50\text{ hertz}$, delivers power to load $R = 10\text{ }\Omega$ through a half-wave controlled rectifier circuit. For a firing-angle delay of $60^\circ$. Determine the following parameters: i) the rectification efficiency ii) form factor iii) voltage ripple factor iv) transformer utilization factor. [20 marks]
Q4. Explain the various Forced Commutation Techniques of Thyristor with suitable circuit diagram and waveforms. [20 marks]

Attempt at least two questions from this Section.

Q5. What are the assumptions for Voltage Commutated Chopper. Explain the principle of operation of Voltage Commutated Chopper with relevant circuit diagrams and waveforms. Also discuss its disadvantages. [20 marks]
Q6. a) Describe the working of Type-E Chopper with relevant circuit diagrams and its operation in all the four quadrants. b) Explain the various control strategies used in Chopper. Also mention which control strategy is preferred over the other and why? [20 marks]
Q7. a) Explain the principle of operation of single-phase full-bridge Voltage Source Inverters with suitable circuit diagram and waveforms. What is the purpose of connecting diodes in anti-parallel with Thyristors in Inverter circuits? Explain how these diodes come into play. b) Explain the two possible methods of external control of ac output voltage obtained from Inverter output terminals with suitable diagrams. [20 marks]
Q8. a) A single-phase bridge type cycloconverter has input voltage of $230\text{ V}$, $50\text{ hz}$ and load of $R = 10\text{ }\Omega$. Output frequency is one-third of input frequency. For a firing angle delay of $30^\circ$, calculate i) rms value of output voltage, ii) rms current of each converter, iii) rms current of each Thyristor and iv) input power factor. b) Explain the principle of operation of single-phase to single-phase bridge-type Step-up Cycloconverter with suitable circuit diagrams and waveforms. [20 marks]