Unbalanced three-phase sinusoidal regimes
Linear power networks

The establishment of an equivalent single-phase diagram is based on the assumption that the three-phase network under study is balanced. This means, on the one hand, that all sources constitute an ideal three-phase system (same amplitude on each phase and phase shifts of 0˚, 120˚ and 240˚), and on the other that all electrical elements of the network are perfectly symmetrical (no phase can be distinguished from the other two).

In reality, things can be different. Imbalances may originate in the sources (mainly synchronous machines) or in the network itself.