Question
Download Solution PDFWhen two-wattmeter method of measurement of power is used to measure power in a balanced three-phase circuit, if the wattmeter readings are zero and positive maximum respectively, then
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
In a two-wattmeter method,
The reading of first wattmeter (W1) = VL IL cos (30 – ϕ)
The reading of the second wattmeter (W2) = VL IL cos (30 + ϕ)
Total power in the circuit (P) = W1 + W2
Total reactive power in the circuit
Power factor = cos ϕ
Calculation:
Given that, W1 = 0 kW
W2 = W kW
⇒ W1 + W2 = 0 + W = W kW
⇒ W1 - W2 = 0 - W = - W kW
Power factor = cos ϕ = cos (- 60°) = 0.5 (lag)
∴ The power factor is 0.5 lagging.
Important Points
|
p.f. angle (ϕ) |
p.f.(cos ϕ) |
W1 [VLIL cos (30 + ϕ)] |
W2 [VLIL cos (30 - ϕ)] |
W = W1 + W2 [W = √3VLIL cos ϕ] |
Observations |
|
0° |
1 |
|
|
√3 VLIL |
W1 = W2 |
|
30° |
0.866 |
|
VLIL |
1.5 VL IL |
W2 = 2W1 |
|
60° |
0.5 |
0 |
|
|
W1 = 0 |
|
90° |
0 |
|
|
0 |
W1 = -ve W2 = +ve |
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