Two wattmeters connected to a three-phase motor measured readings of 5 kW and -1 kW. The total power was calculated as the sum of the wattmeter readings, which was 4 kW. The power factor was calculated from the wattmeter readings using trigonometric functions and was found to be 0.36.

1. Example
When connected to a three-phase motor, two
wattmeters gave readings of 5 kW and—1 kW.

2. Ptotal = W1 + W2
Ptotal = (—1000) + 5000 = 4000
Ptotal = 4 kW

4. tan Φ = √3 x
5 - (-1)
5 + (-1)
tan Φ = √3 x
6
4
tan Φ = √3 x
1.5 = 2.598
Φ = 68.9⁰

5. So as, the power factor (pf) = Cos Φ
Cos Φ = Cos 68.9⁰ = 0.3599 = 0.36
Power factor = 0.36.