18-418: Electric Energy Processing: Fundamentals and Applications Fall Semester, 2009Homework # 4 Due on the class of September, 30thProblem (1) A 150-MVA 15kV/200 kV single-phase power transformer has a per-unit resistance of 1.2 percent and a per unit reactance of 5 percent (data taken from the transformer’s nameplate). Neglect the core losses. a)Find the equivalent circuit referred to the low-voltage side of this transformer. b)Calculate the voltage regulation of this transformer for a full-load current at power factor of 0.8 lagging. c)Assume that the primary voltage of this transformer is a constant 15 kV, and plot the secondary voltage as a function of load current for currents from no-load to full-load. Repeat this process for power factors of 0.8 lagging, 1.0, and 0.8 leading. Problem (2) A three phase transformer connected in Δ-Y with total power is 25-kVA and per phase voltage is 24,000/277V. The open-circuit test as performed on the low-voltage side of this transformer bank, and the following data were recorded: Vline,OC
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Three-phase electric power, transformer bank, three-phase power transformer, transformer’s nameplate