Measurements in three-phase alternating circuits

To measure power in a three-phase circuit with a symmetrical load, two- or three-element wattmeters are used, moreover:
to determine the active power P apply the inclusion scheme:




to determine the reactive power Q:



Total powers are calculated

P = 3Pf = 3UfIf cosφ, where Pf - wattmeter reading.

In the case of measuring the total power in a three-phase circuit with an unbalanced load, at least two wattmeters are used and the result is calculated by the formulas:

P = P1 + P2

,

where P1 and P2 are wattmeter readings.