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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 3 cos p f a s V E P m V I X ϕ = = - a generator delivers P=10 kW at 0.8 lagging power factor 120 3 p V V V = = From the phasor diagram: sin cos f s a AB E X I ϕ ϕ = = and sin s a BC X I ϕ = 10000 34.7 3 cos 3 208 0.8 a P I A V ϕ

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• Spring '08
• Mendrela
• Power factor, Stator, SYNCHRONOUS MACHINE, excitation voltage Ef, mechanical input power, Ef O Ia Vp C Qi Ia Xs B

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