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Please answer each part of the question in detailed manner.
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2. Three identical single-phase transformers are connected to form a three-phase Y-Y transformer bank. Each single-phase transformer is rated 30 kVA, 2300/230-V, 50-Hz. Each of the transformer has the following circuit parameter values: R1 = 0.252, X1 = 1.012, R2 = 0.0252, X2 = 0.112, Rc = 15 k12, XM = 12 k22 (a) Draw the per-phase approximate equivalent circuit of the three-phase transformer referred to the secondary side. If the three-phase transformer is operated at full load with a power factor of 0.9 lagging and at the rated secondary voltage, calculate the voltage regulation and efficiency of the transformer. You may take the secondary voltage as the reference. What is the input power factor? (16 Marks) Note: Question No. 2 continues on page 3. 2 EE3010 (b) If the three-phase transformer is now operated at 50% full load with the same power factor and same rated secondary voltage as that in part (a), what would be the efficiency of the transformer? You may assume that the core losses remain constant. (2 Marks) (c) The single-phase two-winding transformer given earlier is now to be connected as a step-up autotransformer. Choose a suitable connection to give a large KVA rating. Draw the diagram of the step-up autotransformer, indicating the voltages and currents clearly. What is the KVA rating of the autotransformer? (7 Marks)