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University of Hail Electrical Engineering Department Second Semester (092) / 2009 - 2010 Major # 1 Instructor: Dr. Ramzi A. Abdul - Halem Course : Electric Energy Engineering (EE 206) Date : Saturday, April, 3rd, 2010 Period : 60 minutes Student Name: Student ID # : Question 1 / 25 Question 2 / 25 Question 3 / 25 Question 3 / 25 Total Mark / 100 Good Luck EE206 Electric Energy Engineering Major 1 Q1: (25) Points 1. An electrical power supply has a voltage source V = 100 / 0 o V delivers power to two parallel loads of impedances z 2 = 3 – j4 Ω, and z 3 = 5 + j5 Ω , through a feeder of impedance z1 = 8 – j6 Ω. Determine (a) the current drown by each impedance and (b) the complex power taken by each impedance. 2 EE206 Electric Energy Engineering Major 1 Q2: (25) Points A toroid has a circular cross section as shown in Fig. 1. It is made from cast steel with a relative permeability of 2500. Its outer diameter is 24 cm, and its inner diameter is 16 cm. the magnetic flux density in the core is 1.25 tesla measured at the mean diameter of the toroid. (a) Find the current that must be supplied to the coil, which consists of 250 turns. (b) Determine the magnetic flux in the core Figure 1 N = 250 turns 3 EE206 Electric Energy Engineering Q3: (25) Points Major 1 1. A 25-KVA, 2300/230-V, single-phase transformer has a high-voltage winding with a resistance of 1.5 Ω and a leakage reactance of 2.4 Ω. The low-voltage winding has a resistance of 0.015 Ω and a leakage reactance of 0.024Ω. the core loss is 175 W. Find the following: (a) Equivalent impedances referred to the high-voltage winding. (b) Voltage regulation for full load at 230 V and 0.866 power factor lagging (c) The efficiency of the transformed under the condition of part (b) 4 EE206 Electric Energy Engineering Q4: (25) Points Major 1 2. Three single-phase, 20/2.4-KV, ideal transformers are connected to form a three-phase, 10MVA, 34.5/2.4-KV transformer bank. The transformer bank supplies a load of 6 MW at 2.4 KV and 0.85 power factor lagging. (Draw the schematic diagram of the required transformer) a. Determine the line and phase currents at the primary and secondary sides of the transformer. b. Determine the line-to-line and line-to-neutral voltage at the primary and secondary sides of the transformer. 5