Direct Current - Power Conversion - Past Exam Paper, Exams of Power Plant Engineering

Download Direct Current - Power Conversion - Past Exam Paper and more Exams Power Plant Engineering in PDF only on Docsity! Page 1 of 3 CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICHNEOLAÍOCHT CHORCAÍ Semester 1 Examinations 2011/12 Module Title: Power Conversion Module: ELEC7013 School: Electrical & Electronic Engineering Programme title: Bachelor of Engineering in Electrical Engineering – Award Programme Code EELEC_7_Y3 External Examiner(s): Ms M. Desmond, Mr C. Murray. Be Internal Examiner(s): Mr D. Collins Instructions: Answer any four questions. All questions carry equal marks. State any assumption made. Duration: 2 Hours Sitting: Winter 2011 Requirements for this examination: Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt, please contact an Invigilator. Page 2 of 4 Q1. (a) Describe the conditions that have to be fulfilled so that a three phase fully-controlled thyristor converter can transfer power from a DC source to an AC supply. Support your answer with a circuit diagram. (10 marks) (b) A converter of the type in (a) has an AC input line voltage of 4160 V and is operated with a firing angle of 120º. Its output terminals are connected to a 3000 V DC source having an internal resistance of 2  and sufficient inductance to ensure a smooth direct current. Determine the following… (i) the mean direct current; (ii) the power transferred and its direction; (iii) the reactive power and its direction. (15 marks) Q2. (a) Figure 1 shows a circuit diagram for a type of DC converter. Identify the type of converter and describe its principal attributes. (10 marks) (b) For the circuit in (a) and a control ratio (duty cycle) of 0.4, estimate the following… (i) the mean output voltage; (ii) the mean output current; (iii) the output ripple current. (15 marks) Q3. (a) Write a short note on switching loss in a power semiconductor device and indicate the factors that affect it. (5 marks) (b)Figure 2 shows extracts from a manufacturer’s data sheet relating to a MOSFET device. Using the data and calculations, determine the following… (i) the drain-source resistance for an operating temperature of 100ºC; (ii) the conduction power loss for a square wave, ID = 16 A; (iii) the switching loss for the same current at 50 kHz and 400V; (iv) the total power loss for these conditions; (v) the junction temperature with an ambient of 40ºC. (20 marks)