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GATE 2026 EE – Question 19

Power Systems · Symmetrical components, Symmetrical and unsymmetrical fault analysis · 1 mark · Multiple choice

The initial three-phase voltage phasors ($\bar V_A$, $\bar V_B$, and $\bar V_C$) at a bus of a power network are as shown in Case-1. Due to a disturbance, the bus voltage phasors changed in phase by a small angle $\Delta\theta$, and the magnitudes remained the same as depicted in Case-2.

Which one of the following statements is correct about the zero sequence components?

Diagram for GATE 2026 EE question 19
  1. The zero sequence components in Case-1 and Case-2 have the same phase angle and magnitude
  2. The magnitude of the zero sequence component in Case-1 is greater than that in Case-2
  3. The magnitude of the zero sequence component in Case-2 is greater than that in Case-1
  4. The zero sequence components in Case-1 and Case-2 have the same magnitude but different phase angles

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Show answer and explanation

Correct answer: (D) The zero sequence components in Case-1 and Case-2 have the same magnitude but different phase angles

Explanation

The zero sequence component is $\bar V_0=\frac13(\bar V_A+\bar V_B+\bar V_C)$. In Case-2 every phasor is rotated by the same angle $\Delta\theta$, so $\bar V_0$ is multiplied by $e^{j\Delta\theta}$: the magnitude is unchanged and the phase angle changes by $\Delta\theta$.