EE 3140 HW 4 Solution

EE 3140 HW 4 Solution - EE 3410: Homework #4 Solution...

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EE 3410: Homework #4 Solution Problem #1 A 3-phase, 20 kVA, 208 V, 4-pole star-connected synchronous machine has a synchronous reactance of X s = 1.5 per phase. The resistance of the stator winding is negligible. The machine is connected to a 3-phase 208 V infinite bus. Neglect rotational losses. a) The field current and the mechanical input power are adjusted so that the synchronous machine delivers 10 kW at 0.8 lagging power factor. Determine the excitation voltage E f and the power angle δ . b) The mechanical input power is kept constant but the field current is adjusted to make the power factor unity. Determine the percent change in the field current with respect to its value in part (a). Given data: m=3(Y), S=20 kVA, V=208 V, p=4, X s =1.5 , R a =0, P m =0 a) E f V I a X s p X s E f I a I a V ϕ A B C ϕ P Q i O δ p 3c o s pf a s VE Pm V I X ϕ == - a generator delivers P=10 kW at 0.8 lagging power factor 120 3 p V VV From the phasor diagram: sin cos fs a AB E X I ϕϕ and sin sa BC X I = 10000 34.7 3 cos 3 208 0.8 a P I A V == = ⋅⋅ 36.87
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This homework help was uploaded on 04/20/2008 for the course EE 3140 taught by Professor Mendrela during the Spring '08 term at LSU.

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EE 3140 HW 4 Solution - EE 3410: Homework #4 Solution...

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