Measurements of power and current components in unbalanced and distorted three-phase systems

The paper deals with the instantaneous power theory in three-phase circuits by using the instantaneous time phasors of voltage and current. Particularly it is shown that the instantaneous components of the current time-phasor in a rotating reference frame p-q, oriented in such a way that the instantaneous voltage time-phasor points to the p-axis direction, represent the active and reactive currents. These components give rise to instantaneous real and imaginary powers, respectively. The spectral analysis of the above-mentioned time-phasors gives the harmonic symmetrical components of positive and negative sequence of voltage and current three-phase systems