EEE210 – Energy conversion and power system fundamentals Coursework 2

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EE210 - Energy conversion and power system fundamentals

Coursework 2

Department of Electrical and Electronic Engineering

Q1. The primary and secondary windings of a transformer can be connected in different configurations to meet practically any requirement. (30 marks)

a. State four connection types of transformers and draw them. (8 marks)

b. State the advantages and disadvantages of these four connection types of transformers. (16 marks)

c. Usually, we use Y-Δ connection for the step-down transformer and Δ-Y connection for the step-up transformer. Why? (6 marks)

Q2. For three-phase synchronous generator (90-MVA, 173.2-kV) has asynchronous reactance of 18 Ω/phase and anegligible armature resistance. (35 marks)

a. Draw the synchronous machine equivalent circuit and label related parameters. (10 marks)

b. If this generator is delivering rated power to an infinite bus bar with the 0.8 power factor lagging. Determine the magnitude of the generated emf per phase and the power angle δ . (5 marks)

c. What is the maximum three-phase power that the generator can deliver before losing its synchronism if the generated emf is 30 kV per phase? (5 marks)

d. If this generator is delivering 68 MW to the bus bar at the rated voltage with its field current adjusted for a generated emf of 120 kV per phase. Determine the armature current and the power factor. (10 marks)

e. In the condition of (d), state whether power factor is lagging or leading. (5 marks)

Q3. A two-winding transformer rated at 18-kVA, 2400/180-V, 60-Hz has a core loss of 200 W anda full-load copper loss of 500 W. (35 marks)

(a) For the two-winding transformer, derive the currents on the low voltage side and high voltage side. (5 marks)

(b) The above transformer is to be connected as an auto transformer, draw the relevant diagram and label all relevant currents and voltages. (10 marks)

(c) Suppose the auto transformer supplies a load at 120 V from 210 V source. Calculate the kVA load that can

be supplied without exceeding the current rating of the windings. For this part assume an ideal transformer. (10 marks)

(d) Find the efficiency with the kVA loading of part (a) and 0.8 power factor. (10 marks)