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EEE_G544_89_C_2008_2

EEE_G544_89_C_2008_2 - ω(10 3 Starting with the electrical...

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EEE G544 Steady state and dynamics of electric machines Comprehensive Examination Marks: 40 (Open Book) Time: 3 hrs. ______________________________________________________________________________ 1. A three phase 440 V, 50 Hz, four pole induction motor has a per phase stator impedance of 0.38 + j 0.8 and referred standstill rotor impedance of 0.42 + j 1.0 . To limit the current throughout a startup at no load, 75% of the rated voltage is initially applied to the machine through some voltage reduction arrangement. What is the minimum speed the motor should have attained when it is switched to the full load voltage ? Neglect magnetisation current, core loss current, and mechanical losses. ...(10) 2. A three phase AC machine has stator windings carrying balanced three phase currents of the usual nature. If one of the phases is accidentally open circuited, what is the effect on the air gap mmf created by the windings ? Establish your answer by appropriate analysis. How does the air gap mmf appear on a synchronous reference frame revolving at +
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Unformatted text preview: ω ? ...(10) 3. Starting with the electrical equations of the field excited synchronous motor in rotor reference frame, obtain the corresponding equations for a permanent magnet synchronous motor. Assume that the rotor has laminated core with no cages so that electromagnetic damping may be neglected, and that the rotor permanent magnet produces a linkage ψ d along the stator winding d-axis. ...(10) 4. A DC shunt connected motor has armature and field resistance values of r a and r f , corresponding winding leakage inductance values L a and L f , and the mutual inductance between field and armature as L md . While running at initial speed , the electrical terminals are suddenly shorted. Assuming that current dynamics decay before the speed undergoes any substantial change, obtain the decay function for the armature current in s-domain. ...(10) EEE G544/09/Compre 1...
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