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GATE 2016 EE – Question 29

Power Systems · Per-unit quantities, Bus admittance matrix, Gauss-Seidel and Newton-Raphson load flow methods · 1 mark · Multiple choice

In a 100 bus power system, there are 10 generators. In a particular iteration of Newton Raphson load flow technique (in polar coordinates), two of the PV buses are converted to PQ type. In this iteration,

  1. the number of unknown voltage angles increases by two and the number of unknown voltage magnitudes increases by two.
  2. the number of unknown voltage angles remains unchanged and the number of unknown voltage magnitudes increases by two.
  3. the number of unknown voltage angles increases by two and the number of unknown voltage magnitudes decreases by two.
  4. the number of unknown voltage angles remains unchanged and the number of unknown voltage magnitudes decreases by two.

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Show answer and explanation

Correct answer: (B) the number of unknown voltage angles remains unchanged and the number of unknown voltage magnitudes increases by two.

Explanation

At a PV bus the voltage magnitude is fixed and only the angle is unknown. At a PQ bus both the magnitude and the angle are unknown. Converting two PV buses to PQ leaves the angles unknown as before, but adds two unknown voltage magnitudes.