Thyristor Controlled Series Capacitor - Power Electronics - Past Exam Paper, Exams of Power Electronics

Download Thyristor Controlled Series Capacitor - Power Electronics - Past Exam Paper and more Exams Power Electronics in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Electrical Engineering — Award (EELEC_7_Y3) Summer 2008 Power Electronics (Time: 3 Hours) Answer FIVE questions. All questions carry equal marks. Prof. E. McQuade Mr. M. Hennessy Mr. D. A. Collins Q1. (a) Briefly describe how an AC converter can be used for controlling the product temperature in a plastic extrusion process. [10] (b) An AC converter comprising a thyristor pair is connected between a single phase supply and a resistive load. If the thyristors are triggered using integral cycle control with a process pattern that repeats every 20 (electrical) cycles, (i) estimate the number of ON cycles for 65% maximum power. (ii) sketch the current waveform for a process cycle under this condition. [10] Q2. (a) The DC power supply for an electric tram system is derived from a 12-pulse diode rectifier and associated transformer. Sketch the circuit diagram for this scheme and explain why a 12-pulse scheme is appropriate. [10] (b) If the tram supply in (a) is rated 750 V DC, the transformer primary is connected in star, it has an input line voltage is 400 V and all volt drops are neglected, estimate the transformer ratios involved. [10] 2 Q3. (a) Describe the principle of operation of a thyristor controlled series capacitor (TCSR) for power control on a high voltage transmission line. [8] (b) A transmission line operates at 230 kV, it has a maximum rated current of 1050 A and an inductive reactance of 54 Ω per phase. The line is fitted with four stages of TCSR, each having a capacitive reactance of 12 Ω and a (shunt) inductive reactance of 1.71 Ω. Calculate the following… (i) The effective impedance of one TCSR stage with its thyristors ON. (ii) The maximum transmission power without overloading the line. (iii) The optimum configuration of the TCSR for a sending end voltage of 218 kV, a receiving end voltage of 237 kV and a phase angle of 15º between them. [12] Q4. (a) With the help of a circuit diagram and switching waveforms for one cycle, describe how a single phase voltage source H-bridge inverter can produce a quasi-square wave output voltage. [10] (b) An inverter has a quasi-square wave output voltage with a peak value of 100 V and a conduction angle of 120° in each half cycle. Determine the RMS value of the fundamental and the first three significant harmonics and sketch the harmonic spectrum for the output voltage. [10] Q5. (a) Figure 1 shows extracts from a manufacturer’s data sheet for an IGBT module. Use the data sheet to establish the forward volt drop in one IGBT for a collector current of 50 A and a gate voltage of 13 V. [5] (b) A H-bridge inverter is assembled using two of the modules referred to in (a). The inverter generates a square wave output with a peak voltage of 300 V, a peak current of 50 A and a frequency of 50 kHz. For these conditions, estimate the conduction and switching losses in each module. If the thermal resistance between the module case and heat sink is 0.05 K/W and the ambient temperature is 40°C, calculate the junction temperature. [15] Q6. (a) Study the circuit diagram in Figure 2 and then briefly explain the action of the circuit and the role of the main components / assemblies. [8] (b) A battery charger delivers its DC output at 72 V from a step down converter having an input voltage of 360 V. The charging requirement is for a mean current of 25 A and a maximum ripple current of 2 A. If the transistor ON time is fixed at 200 µs, estimate the switching frequency, the mean input current, the mean diode current and the inductance. [12]