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GATE 2018 EE – Question 15

Electrical and Electronic Measurements · Measurement of voltage, current, power, energy and power factor · 1 mark · Multiple choice

Two wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other (both positive), then the power factor of the load is

  1. 0.532
  2. 0.632
  3. 0.707
  4. 0.866

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Correct answer: (D) 0.866

Explanation

$\tan\phi=\sqrt3\frac{W_1-W_2}{W_1+W_2}=\sqrt3\frac{2-1}{2+1}=\frac{1}{\sqrt3}$, so $\phi=30^\circ$ and the power factor is $0.866$.