Correct Answer - Option 2 : When power factor is changed from lagging to leading, the reading of W
1 and W
2 get interchanged.
Concept:
Two-wattmeter method:
The reading of first wattmeter (W1) = VL IL cos (30 + ϕ)
The reading of second wattmeter (W2) = VL IL cos (30 - ϕ)
Total power in the circuit (P) = W1 + W2
Total reactive power in the circuit \(Q=\sqrt{3}\left( {{W}_{1}}-{{W}_{2}} \right)\)
Power factor = cos ϕ
\(ϕ =\text{ta}{{\text{n}}^{-1}}\left( \frac{\sqrt{3}\left( {{W}_{1}}-{{W}_{2}} \right)}{{{W}_{1}}+{{W}_{2}}} \right)\)
If,
W1 > W2: The power factor consider as lagging
W2 > W1: The power factor consider as leading
Hence, When the power factor is changed from lagging to leading, the reading of W1 and W2 get interchanged.