GATE 2015 EE (EE2) – Question 26

Power Systems · System stability concepts, Equal area criterion · 1 mark · Multiple choice

The synchronous generator shown feeds an infinite bus through two short lossless lines and is initially steady. Mechanical input and internal-voltage magnitude E stay constant. At t1 one line is tripped at both ends without a fault, producing a stable transient. Which rotor-angle waveform is correct?

Diagram for GATE 2015 EE (EE2) question 26

Option A in the figure
Option B in the figure
Option C in the figure
Option D in the figure

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Show answer and explanation

Correct answer: (A) Option A in the figure

Explanation

Removing one parallel line raises transfer reactance and reduces the power-angle curve's maximum. At the unchanged initial angle, electrical output drops below mechanical input, so the rotor accelerates and δ initially increases.

The new stable equilibrium requires a larger positive angle. A stable damped transient oscillates around that higher value. Only graph **A** has the correct initial positive angle, initial upward motion and higher eventual operating angle. The source does not quantify damping; the graph illustrates the stable transient with damping.

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