A 25 kVA, 400 V, delta-connected three-phase cylindrical synchronous generator needs 5 A field current for rated short-circuit armature current. At that field current, open-circuit voltage is 360 V. Neglect armature resistance and saturation. At rated load and voltage with 0.8 leading pf, voltage regulation in percent is ________.
For delta connection, rated phase current is $25000/(3\cdot400)=20.8333$ A. The synchronous reactance is 360/20.8333=17.28 Ω, so at rated current XsI=360 V.
Taking terminal phase voltage as real, leading current has normalized phasor 0.8+j0.6. Generated emf is $E=400+j360(0.8+j0.6)=184+j288$ V.
Its magnitude is 341.760 V. Regulation is $100(|E|-400)/400=$ **−14.56%**, within −15 to −14%.
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