Correct Answer - Option 4 : Load is purely inductive
Concept:
In a 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
\(ϕ =\text{ta}{{\text{n}}^{-1}}\left( \frac{\sqrt{3}\left( {{W}_{1}}-{{W}_{2}} \right)}{{{W}_{1}}+{{W}_{2}}} \right)\)
Calculation:
The reading of wattmeter 1 is proportional to cos (30 + ϕ)
The reading of wattmeter 1 is proportional to cos (30 - ϕ)
The readings of both the wattmeters will be equal and opposite only when the phase difference is 90°.
The phase difference of 90° is possible when the load is either purely inductive or purely capacitive.
