Therefore, using only four power measurements, the overall active and reactive powers can be obtained.
The main disadvantage of this method is that the four measurements are not simultaneous; therefore, any load variations during the measurement would cause a loss in accuracy. In this case, a variation proposed by Righi can be used.
In this variation, three wattmeters are connected as shown in Figure 3.22 and give simultaneously P12, P32, and P2(31).