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Pharos University Faculty of Engineering Department of Electrical Engineering SEMESTER: 3rd level - 5th semester Course Title: Electrical Power Engineering 1 Instructor: Dr. Sahar Abd El Moneim Academic Year: Fall 2012/13 Course Code: EE272 Sheet-1 Three-Phase System Three-Phase System 1- A balanced three-phase Y-connected generator with positive sequence has an impedance of 0.2 +j0.5 / and an internal voltage of 120 V/. The generator feeds a balanced three-phase Y-connected load having an impedance of 39 +j28 /. The impedance of the line connecting the generator to the load is 0.78 +j1.5 /. The a-internal voltage of the generator is specified as the reference phasor. a) b) c) d) e) f) g) h) i) j) k) l) Construct the a-phase equivalent circuit of the system. Calculate the three line currents IaA, IbB and IcC. Calculate the three –phase voltages at the load VA, VB and VC. Calculate the line voltages VAB , VBC and VCA at the terminals of the load. Calculate the phase voltages at the terminals of the generator Va , Vb and Vc . Calculate the line voltages Vab, Vbc and Vca at the terminals of the generator. Calculate the average power per phase delivered to the Y-connected load. Calculate the total average power delivered to the load. Calculate the total average power lost in the line. Calculate the total average power lost in the generator. Calculate the total number of magnetizing Vars absorbed by the load. Calculate the total complex power delivered by the source. Assignment: 2- A balanced three-phase Y-connected generator with line Voltage = 800v and an internal impedance of Zs=0.4+j1 / . The Transmission line impedance connecting the generator with the loads Zl= 1+2j / , whereas the neutral impedance Zn=5+12j / . The generator is connected to unbalanced three-phase Y-connected load : Z1=20+30j / Z2=15-10j / Z3=20+20j / Find : a) Calculate the three line currents . b) Calculate the neutral Voltage Vn. c) Calculate the neutral current In. d) Calculate the three –phase voltages at the load VA, VB and VC. e) Calculate the line voltages VAB , VBC and VCA at the terminals of the load. f) Calculate the generator complex power and apparent Power . g) Calculate the total average power delivered to the load. h) Calculate the total number of magnetizing Vars absorbed by the load. i) Calculate the total average power lost in the line and source impedance.