GATE EE 2017 Set 2 — Question 44
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Electrical Machines → Synchronous Machines → Synchronous Reactance & Regulation
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Question
A 25 kVA, 400 V, -connected, 3-phase, cylindrical rotor synchronous generator requires a field current of 5 A to maintain the rated armature current under short-circuit condition. For the same field current, the open-circuit voltage is 360 V. Neglecting the armature resistance and magnetic saturation, its voltage regulation (in % with respect to terminal voltage), when the generator delivers the rated load at 0.8 pf leading, at rated terminal voltage is ___________.
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Solution
1.Calculate rated phase current ():
Since the generator is -connected, the phase voltage is equal to the line voltage V.Rated phase current A.
2.Calculate synchronous reactance ():
From the short-circuit test, A at A.From the open-circuit test, V at A. Since it is -connected, V.
.
3.Calculate excitation voltage () for 0.8 pf leading:
For leading power factor, the phasor equation is . In magnitude form:Given , so .
V.
4.Calculate voltage regulation:
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