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GATE 2026 EE – Question 22

Electrical Machines · Synchronous machines: cylindrical and salient pole machines, performance and characteristics, regulation and parallel operation of generators, starting of synchronous motors · 1 mark · Multiple choice

The figure shows the single-line diagram of a synchronous generator delivering $P=50$ MW of power at unity power factor to an infinite bus.

$\bar I_s$ denotes the stator current phasor. If the field excitation is increased, which one of the following options correctly describes its effect on the stator current, power factor, and load angle of the machine?

Diagram for GATE 2026 EE question 22
  1. Stator current increases, power factor becomes lagging, load angle remains the same
  2. Stator current decreases, power factor becomes leading, load angle remains the same
  3. Stator current increases, power factor becomes lagging, load angle decreases
  4. Stator current increases, power factor becomes leading, load angle increases

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Show answer and explanation

Correct answer: (C) Stator current increases, power factor becomes lagging, load angle decreases

Explanation

The real power stays 50 MW. Raising the excitation ($E_f$) makes the machine over-excited, so it supplies reactive power: the current gets a lagging component, the stator current magnitude rises and the power factor becomes lagging. Since $P\propto E_fV\sin\delta$ is constant, a larger $E_f$ means a smaller $\sin\delta$: the load angle decreases.