Department of Electrical Engineering Indian Institute of Technology, Kharagpur Electrical Machines(EE2l002) Date: 25th April, 2016 AN 2nd Year EE Exam Halls: F116, F142, NR221,NR222 & NR321 104 students Time: 3 hours. Spring End Semester Exam. 2015-2016 Full Marks: 100 Instructions: Attempt ANY FIVE questions. Intermediate calculation steps must be shown. 1. (a) With reference to a 3-phase synchronous generator, explain with phasor diagram the concept of armature reaction reactance. Why is this reactance called a fictitious reactance? [5] (b) Draw the phasor diagram of an over-excited non-salient pole synchronous motor having per phase z, = ra + jxs. [5] (c) Draw the phasor diagram of salient pole over excited synchronous motor having negligible armature resistance and direct and quadrature axis reactances are Xd and x q . [5] (d) A Salient pole synchronous generator has negligible armature resistance and with direct & quadrature axis reactances Xd and x q . The generator is working steadily connected to the bus with zero excitation. Under this condition it is delivering maximum power. Draw the phasor diagram and find out the power factor at which it is operating. [5] 2. A 3-phase, star connected, 6 pole, 50 Hz synchronous generator has the following data: Diameter of the inner bore: Length of the machine: Phase spread: Total number of slots: Number of conductors/slot: Coils are short chorded: 30 em 25 em 60° 72 10 by one slot pitch Air gap flux density distribution is given to be: b = 0.9 sine + 0.2 sin3e + 0.1 sin5e Wb/m 2 (a) (b) (c) (d) calculate flux per pole due to fundamental, 3rd harmonic and 5th harmonic components. [3] calculate distribution factors for fundamental, 3rd harmonic and 5th harmonic components. [3] calculate the pitch factors due for fundamental, 3rd harmonic and 5th harmonic components. [3] ponents. (e) Also calculate the line to line voltage. calculate per phase induced voltages due to fundamental, 3rd harmonic and 5th harmonic com- [8] [3] 3. (a) Explain the basis of Blondel's two reaction theory for analyzing a salient pole synchronous machine. [5] (b) A salient pole synchronous generator has per phase reactances Xd and Xq along d and q axis respectively with armature resistance raper phase. The generator is supplying to the bus an armature current of fa at a power factor angle e lagging. Assume the per phase bus voltage to be V. Draw the phasor diagram showing bus voltage, excitation voltage and voltage drops in r a, Xd and x q . Also explain clearly how the position of d and q axis can be ascertained from the knowledge of bus voltage, armature current and e. Also find out an expression for power delivered to the bus in terms of E, V, 6, Xd and x q . [15] Please Turn Over 1