The paper revisits and tries to present in an actual perspective the innovative theory introduced in mid 1980s by Professor Ţugulea concerning the active power flow in electrical three-phase networks supplying non-linear unbalanced loads. In the context of today’s challenges and energy consumption profile, the negative effects of this kind of loads inflicted to the linear balanced ones through unnecessary power injection on the negative sequence and high-order harmonics are evaluated. The present study proposes a slightly different definition for the original residual active power definition, to take into account the dc component and its associated power. Finally, the conservative nature of the symmetry, non-symmetry and residual active and reactive powers introduced by the original theory and its extension are demonstrated and interpreted on test-circuits simulated using the Orcad Lite 16.6 software PSpice component.

Keywords: Three-phase unbalanced circuits, Ţugulea theory, Non-linear loads, Non-sinusoidal regime, Non-symmetry active power, Residual active power, Non-symmetry reactive power, Residual reactive power, Active power conservation, Reactive power conservation, Power quality