Royal Melbourne Institute of TechnologyEEET 2304PP_2015_HK_EEET2304_exam_tri1_2015 April_Questions.pdf

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Q1. A balanced three phase wye-connected motor draws 5 MW at a lagging power factor of 0.86 from a 33kV (line-line) 50Hz supply. 1.a. Calculate the supply line current. [6 marks] 1.b. Calculate the... supply line current if the motor is delta-connected, while drawing the same load of 5MW at a lagging power factor of 0.86. [4 marks] The motor is now restored to the wye-connected configuration and the loading condition considered in 1.a. A wye-connected capacitor bank is connected in parallel to the motor to improve the overall power factor as seen from the supply. 1.c. Determine the capacitor value required to improve the power factor to 0.95 lagging. [5 marks] 1.d. Calculate the overall power factor seen by the supply if the capacitor bank is connected in delta, with the capacitance value determined in 1.c. [5 marks] Total Marks for Question 1 = 20 marks Q2. Characterisation tests have been performed on a single phase 20 kVA, 2500 V / 400 V, 50 Hz transformer, yielding the following data: x Open Circuit test at rated primary volts, measured real power = 1600 W, measured primary current = 1.1 A. x Short Circuit test at rated primary current, measured real power = 1400 W, measured primary voltage = 400 V. 2.a. Calculate the primary referred circuit parameters for the transformer based on the approximate equivalent circuit. [10 marks] 2.b. Calculate the required primary side voltage when the secondary side of the transformer delivers rated kVA at 0.7 p.f. lagging at rated secondary voltage. [5 marks] 2.c. Calculate the transformer efficiency for the loading condition described in part 2.b. [5 marks] Total Marks for Question 2 = 20 marks [Show More]

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